Pseudopterosin synthesis from a chiral cross-conjugated hydrocarbon through a series of cycloadditions

Substituent-dependent [4+2] or [2+2] cycloadditions of phenylallenyl phosphine oxides with arynes

A [4+2] cycloaddition strategy to assemble phenanthren-9-yldiphenylphosphine oxides is reported. This reaction relies on the strategic use of readily available phenylallenyl phosphine oxides as dienes to participate in [4+2] cycloaddition with arynes. Notably, benzo[b][1,4]oxaphosphinin-4-iums can be controllably synthesized by simply tuning the substituents in the phosphine oxide unit through a [2+2] cycloaddition cascade.

Marine Bioactive Molecules as Inhibitors of the Janus Kinases: A Comparative Molecular Docking and Molecular Dynamics Simulation Approach

A treasure trove of naturally occurring biomolecules can be obtained from sea living organisms to be used as potential antioxidant and anti-inflammatory agents. These bioactive molecules can target signaling molecules involved in the severity of chronic autoimmune diseases such as rheumatoid arthritis (RA). The intracellular tyrosine kinases family, Janus kinases (JAKs, includes JAK1, JAK2, and JAK3), is implicated in the pathogenesis of RA through regulating several cytokines and inflammatory processes. In the present study, we conducted molecular docking and structural analysis investigations to explore the role of a set of bioactive molecules from marine sources that can be used as JAKs' specific inhibitors. Around 200 antioxidants and anti-inflammatory molecules out of thousands of marine molecules found at the Comprehensive Marine Natural Products Database (CMNPD) website, were used in that analysis. The details of the interacting residues were compared to the recent FDA approved inhibitors tofacitinib and baricitinib for data validation. The shortlisted critical amino acids residues of our pharmacophore-based virtual screening were LYS905, GLU957, LEU959, and ASP1003 at JAK1, GLU930 and LEU932 at JAK2, and GLU905 and CYS909 of JAK3. Interestingly, marine biomolecules such as Sargachromanol G, Isopseudopterosin E, Seco-Pseudopterosin, and CID 10071610 showed specific binding and significantly higher binding energy to JAK1 active/potential sites when being compared with the approved inhibitors. In addition, Zoanthoxanthin and Fuscoside E bind to JAK2's critical residues, GLU930 and LEU932. Moreover, Phorbaketal and Fuscoside E appear to be potential candidates that can inhibit JAK3 activity. These results were validated using molecular dynamics simulation for the docked complexes, JAK1(6sm8)/SG, JAK2 (3jy9)/ZAX, and JAK3 (6pjc)/Fuscoside E, where stable and lower binding energy were found based on analyzing set of parameters, discussed below (videos are attached). A promising role of these marine bioactive molecules can be confirmed in prospective preclinical/clinical investigations using rheumatoid arthritis models.

Heavy Heterodendralenes: Structure and Reactivity of Phosphabora[3]dendralenes

The incorporation of phosphorus and boron into [3]dendralenes provides access to heavy heterodendralenes, a new class of main-group precursor to "doped" polycyclic hydrocarbons. [n]Dendralenes are a core class of unsaturated hydrocarbons built from geminally connected polyenes; the resulting arrangement of conjugated C═C bonds enables [n]dendralenes to undergo reactions that allow rapid access to complex polycyclic compounds. The increasing technological and synthetic importance of main-group-containing polycyclic hydrocarbons and their analogues makes new routes to access such systems highly attractive. Here we report the preparation of the first heavy heterodendralenes in the form of phosphorus- and boron-containing [3]dendralenes, prepared by a ring-opening reaction of a 1,2-phosphaborete. We reveal the electronic effect of P/B incorporation and demonstrate that, like their hydrocarbon analogues, phosphabora[3]dendralenes undergo diene-transmissive cycloaddition chemistry.

A Rapid Aza-Bicycle Synthesis from Dendralenes and Imines

The diene-transmissive 2-fold Diels-Alder sequence between carbon-based dienophiles and [3]dendralenes is becoming an established method for polycarbocycle synthesis. Here, we demonstrate for the first time that imines are competent participants in intermolecular formal [4 + 2] cycloadditions with dendralenes. After a second Diels-Alder process with a carbadienophile, hexahydro- and octahydro-isoquinoline structures are formed. The formal aza-Diels-Alder reaction, which requires Lewis acid promotion, proceeds in high regio- and stereoselectivity under optimized conditions. ωB97XD/Def2-TZVP//M06-2X/6-31+G(d,p) calculations reveal a stepwise ionic mechanism for the formal aza-dienophile cycloadditions and also explain an unexpected Z → E olefin isomerization of a non-reacting C═C bond in the first formal cycloaddition.

Simplifying the Synthesis of Nonproteinogenic Amino Acids via Palladium-Catalyzed δ-Methyl C-H Olefination of Aliphatic Amines and Amino Acids

Transition metal-catalyzed directing group assisted C-H functionalizations provide a straightforward access to a wide variety of nonproteinogenic amino acids. While altering the side chain of an existing natural amino acids is one way, introducing a functional group to an aliphatic amine to synthesize versatile unnatural amino acids is another exciting avenue. In this work, we explore both the possibilities by the palladium-catalyzed δ-C(sp³)-H olefination of aliphatic amines and amino acids. A diverse substrate scope including sequential difunctionalizations followed by post synthetic transformations were achieved to understand the applicability of the current protocol. An in-depth mechanistic study was carried out to learn the mode of the reaction pathway.

Spin-Space-Encoding Magnetic Resonance Imaging: A New Application for Rapid and Sensitive Monitoring of Dynamic Swelling of Confined Hydrogels

An NMR method based on the gradient-based broadening fingerprint using line shape enhancement (PROFILE) is put forward to precisely and sensitively study hydrogel swelling under restricted conditions. This approach achieves a match between the resonance frequency and spatial position of the sample. A three-component hydrogel with salt ions was designed and synthesized to show the monitoring more clearly. The relationship between the hydrogel swelling and the frequency signal is revealed through the one-dimensional imaging. This method enables real-time monitoring and avoids changing the swelling environment of the hydrogel during contact. The accuracy of this method may reach the micron order. This finding provides an approach to the rapid and non-destructive detection of swelling, especially one-dimensional swelling, and may show the material exchange between the hydrogel and swelling medium.

A General Stereoselective Synthesis of [4]Dendralenes

The first general synthesis of branched tetraenes ([4]dendralenes) involves two or three steps from inexpensive, commodity chemicals. It involves an unprecedented variation on Suzuki-Miyaura cross-coupling, generating two new C-C bonds in a one-flask operation with control of diastereoselectivity. The broad scope of the method is established through the synthesis of more than 60 diversely substituted [4]dendralene molecules, along with substituted buta-1,3-dienes and other [n]dendralenes. [4]Dendralenes are demonstrated to be significantly more kinetically stable than their well-known [3]dendralene counterparts. The first stereoselective synthesis of these compounds is also reported, through the catalyst-controlled generation of both E- and Z-diastereomeric products from the same precursor. Novel, through-conjugated/cross-conjugated hybrid molecules are introduced. The first selective dienophile cycloadditions to substituted [4]dendralenes are reported, thus paving the way for applications in target-oriented synthesis.

Total Synthesis of Matrine Alkaloids

The total synthesis of three diastereomeric matrine natural products is reported. The 8-step synthesis commences with simple acyclic precursors, forms all 4 rings of the tetracyclic natural product framework, and forges 10 of the 20 covalent bonds of the target structure. A cross-conjugated triene is positioned at the core of an acyclic branched structure. This precursor collapses to the tetracyclic natural product framework through an orchestrated sequence of two separate intramolecular cycloadditions. A subsequent, late-stage hydrogenation is accompanied by strain-release redox epimerizations to deliver the three natural products. An unprecedented carba-analogue is prepared in the same way. Semisynthetic manipulations of matrine provide access to 10 additional natural products.

Divergent Reactivity of Phosphorylated and Related Allenes: [4 + 2] Cycloaddition with 3,6-Diphenyltetrazine, Self-Addition Leading to Dimers and [Pd]-Complex Formation

Phosphorus-based naphthalenes are formed by self-dimerization-cum-cyclization of α-aryl allenylphosphonates or allenylphosphine oxides using catalytic Pd(OAc)₂in the presence of PPh₃ and Et₃N . This reaction involves [4 + 2]-cycloaddition with the (β,γ) double bond of one allene as the dienophile; the double bonds at the α-aryl-(β',γ') group and (α,β)-carbons of the second allene act as the diene part. A subsequent proton shift also takes place. Upon treating allenylphosphine oxides with Pd(OAc)₂ [stoichiometry 2:1] in the presence of PPh₃/Ag₂CO₃, a [Pd]-complex is isolated and structurally characterized. This complex can be used as a catalyst for C-C bond-forming reactions of phosphorus-based allenes with 2-iodophenol. Densely substituted 3,6-diphenylpyridazines are conveniently obtained in excellent yields by a thermally induced regioselective Inverse Electron Demand Diels-Alder (IEDDA) reaction of allenes with 3,6-diphenyltetrazine, followed by a [1,3]-H shift.

Enantioselective oxa-Diels-Alder Sequences of Dendralenes

Diene-transmissive hetero-Diels-Alder sequences involving carbonyl dienophiles are reported for the first time. High enantioselectivities are achieved in the reaction of phenylglyoxal with a broad range of dendralene structures, through the optimization of a Pd2+ catalyst system. The initial catalyst-controlled enantioselective oxa-Diels-Alder (ODA) cycloaddition to a [3]dendralene generates a dihydropyran carrying a semicyclic diene. This participates in a subsequent catalyst or substrate-controlled Diels-Alder reaction to generate sp3 -rich fused polycyclic systems containing both heterocycles and carbocycles. Computational investigations reveal a concerted asynchronous mechanism. π-Complexation of a diene C=C bond to Pd2+ occurs in both the pre-transition state (TS) complex and in cycloaddition TSs, controlling stereoselectivity. A formal enantioselective [4+2]cycloaddition of a CO2 dienophile is demonstrated.

Allenes in Diels–Alder Cycloadditions

For a long time, allenes—and cumulenic systems in general—played a relatively minor role in Diels–Alder cycloadditions. This situation has changed, since allenes are more readily available and as their unique stereochemical features in [4+2]cycloadditions are more widely recognized. This review presents a comprehensive overview of allenes in Diels–Alder processes using selected examples. Allenes in dienes, dienophiles and cycloadducts are covered, inter- and intramolecular Diels–Alder cycloadditions are discussed, and stereochemical features of the addition process are described. Areas of emerging importance are also covered, including allenic components in dehydro-Diels–Alder processes, and dendralenic allenes in Diels–Alder sequences for the rapid generation of target-relevant molecular complexity. Preparatively useful methods for allenic precursor synthesis are also discussed.

1 Introduction

2 Allenic Dienes

2.1 Vinylallenes

2.2 Bisallenes

2.3 Cross-conjugated Allenes

3 Allenic Dienophiles

4 Intramolecular Diels–Alder Cycloadditions

5 Allenic Cycloadducts

6 Conclusions and Outlook

Substituted Tetraethynylethylene-Tetravinylethylene Hybrids

A general synthetic approach to molecular structures that are hybrids of tetraethynylethylene (TEE) and tetravinylethylene (TVE) is reported. The synthesis permits the controlled preparation of many previously inaccessible structures, including examples with different substituents on each of the four branching arms. Most substituted TVE-TEE hybrids are found to be significantly more robust compounds than their unsubstituted counterparts, enhancing the prospects of their deployment in conducting materials and devices. Their participation in pericyclic reaction cascades, leading to sp³-rich polycycles, is demonstrated. The utilization of TEE-TVE hybrids as building blocks for larger acyclic, through/cross-conjugated hydrocarbon frameworks is also established. Aryl-substituted TEEs, TVEs, and their hybrids are fluorescent, with some exhibiting aggregation-induced emission enhancement. The structural requirements are defined and explained, setting the scene for applications as fluorescent probes and organic light-emitting diodes.

Total Synthesis of (+)-Erogorgiaene and the Pseudopterosin A-F Aglycone via Enantioselective Cobalt-Catalyzed Hydrovinylation

Due to their pronounced bioactivity and limited availability from natural resources, metabolites of the soft coral Pseudopterogorgia elisabethae, such as erogorgiaene and the pseudopterosines, represent important target molecules for chemical synthesis. We have now developed a particularly short and efficient route towards these marine diterpenes exploiting an operationally convenient enantioselective cobalt-catalyzed hydrovinylation as the chirogenic step. Other noteworthy C-C bond forming transformations include diastereoselective Lewis acid-mediated cyclizations, a Suzuki coupling and a carbonyl ene reaction. Starting from 4-methyl-styrene the anti-tubercular agent (+)-erogorgiaene (>98 % ee) was prepared in only 7 steps with 46 % overall yield. In addition, the synthesis of the pseudopterosin A aglycone was achieved in 12 steps with 30 % overall yield and, surprisingly, was found to exhibit a similar anti-inflammatory activity (inhibition of LPS-induced NF-κB activation) as a natural mixture of pseudopterosins A-D or iso-pseudopterosin A, prepared by β-D-xylosylation of the synthetic aglycone.

Palladium-Catalyzed Oxidative Coupling of the Allenic C-H Bond with α-Diazo Esters: Synthesis of [3]Dendralenes

A palladium-catalyzed highly regio- and stereoselective allenic C-H oxidative coupling with α-diazo esters is developed. The reaction pathway involves allylic palladium carbene as the key intermediate, which is followed by a carbene migratory insertion process. The reaction proceeds efficiently under mild conditions without external base, providing substituted [3]dendralenes bearing various functional groups.

[n]Dendralenes as a Platform for Selective Catalysis: Ligand-Controlled Cu-Catalyzed Chemo-, Regio-, and Enantioselective Borylations

We report the development of two complementary methods for the Cu-catalyzed anti-Markovnikov borylation of one specific olefin in 2-substituted [n]dendralenes (n = 3-6). The first protocol operates with a bisphosphine ligand and occurs with high regio- and chemoselectivity for the terminal double bond, independently of the number of cross-conjugated alkenes. We show that the use of a chiral phosphanamine ligand enables the highly chemo-, regio-, and enantioselective borylation of the alkene cross-conjugated with the terminal olefin in [n]dendralenes.

Copper-catalyzed protoboration of borylated dendralenes: a regio- and stereoselective access to functionalized 1,3-dienes

A copper-catalyzed protoboration of borylated dendralenes is reported. The method employs an NHC-Cu catalyst and provides access to 1,4-addition products with excellent levels of chemo-, regio- and stereoselectivity. The resulting diene bis(boronates) are oxidized to the corresponding diene diols which are synthetically versatile building blocks.

Total synthesis of endiandric acid J and beilcyclone A from cyclooctatetraene

The endiandric acids are classic targets in natural product synthesis. The spectacular 8π/6π-electrocylisation/intramolecular Diels-Alder (8π/6π/IMDA) reaction cascade at the heart of their biosynthesis has inspired practitioners and students of pericyclic chemistry for nearly forty years. All previous synthetic approaches have sought to prepare a linear tetraene and thereby initiate the cascade. In this communication we demonstrate the use of cyclooctatetraene to rapidly intercept the 8π/6π/IMDA cascade at the cyclooctatriene stage. Endiandric acid J and beilcyclone A are prepared for the first time in six and five steps, respectively. The strategy features a tactical overall anti-vicinal difunctionalisation of cyclooctatetraene through SN2' alkylation of cyclooctatetraene oxide followed by an intriguing tandem Claisen rearrangement/6π-electrocyclisation from the corresponding vinyl ether. This rapidly constructs an advanced bicyclo[4.2.0]octadiene aldehyde intermediate. Olefinations and intramolecular Diels-Alder cycloadditions complete the syntheses. This establishes a short and efficient new path to the endiandric acid natural products. DFT modelling predicts thermal racemisation of bicyclo[4.2.0]octadiene intermediates, dashing hopes of enantioselective synthesis.

Asymmetric Total Syntheses of Di- and Sesquiterpenoids by Catalytic C-C Activation of Cyclopentanones

To show the synthetic utility of the catalytic C-C activation of less strained substrates, described here are the collective and concise syntheses of the natural products (-)-microthecaline A, (-)-leubehanol, (+)-pseudopteroxazole, (+)-seco-pseudopteroxazole, pseudopterosin A-F and G-J aglycones, and (+)-heritonin. The key step in these syntheses involve a Rh-catalyzed C-C/C-H activation cascade of 3-arylcyclopentanones, which provides a rapid and enantioselective route to access the polysubstituted tetrahydronaphthalene cores presented in these natural products. Other important features include 1) the direct C-H amination of the tetralone substrate in the synthesis of (-)-microthecaline A, 2) the use of phosphoric acid to enhance efficiency and regioselectivity for problematic cyclopentanone substrates in the C-C activation reactions, and 3) the direct conversion of serrulatane into amphilectane diterpenes by an allylic cyclodehydrogenation coupling.

Concise Formal Synthesis of the Pseudopterosins via Anionic Oxy-Cope/Transannular Michael Addition Cascade

An anionic oxy-Cope/transannular Michael addition cascade converts a spirocyclic architecture-readily available by Diels-Alder cycloaddition-into the hydrophenalene carbon skeleton of the pseudopterosin aglycones. Oxidation of the resulting cyclohexenone ring to the phenol that is characteristic of the targets completes a short formal synthesis.

Synthesis and Properties of 2,3-Diethynyl-1,3-Butadienes

The first general preparative access to compounds of the 2,3-diethynyl-1,3-butadiene (DEBD) class is reported. The synthesis involves a one-pot, twofold Sonogashira-type, Pd⁰ -catalyzed coupling of two terminal alkynes and a carbonate derivative of a 2-butyne-1,4-diol. The synthesis is broad in scope and members of this structural family are kinetically stable enough to be handled using standard laboratory techniques at ambient temperature. They decompose primarily through heat-promoted cyclodimerizations, which are impeded by alkyl substitution and accelerated by aryl or alkenyl substitution. An iterative sequence of these unprecedented Sonogashira-type couplings generates a new type of expanded dendralene. A suitably substituted DEBD carrying two terminal alkyne groups undergoes Glaser-Eglinton cyclo-oligomerization to produce a new class of expanded radialenes, which are chiral due to restricted rotation about their 1,3-butadiene units. The structural features giving rise to atropisomerism in these compounds are distinct from those reported previously.

A general synthesis of dendralenes

The first broad spectrum dendralene synthesis permits the widest structural and substituent variation and promotes applications in step economic synthesis.

The first general synthetic approach to substituted [3]- and higher dendralenes is reported. Fifty-one mono- through to penta-substituted dendralenes carrying alkyl-, cycloalkyl-, alkenyl-, alkynyl-, aryl- and heteroaryl-substitutents are accessed, and the first (E)/(Z)-stereoselective syntheses of dendralenes are reported (twenty-eight examples). The approach involves twofold Pd(0)-catalyzed Negishi couplings of 1,1-dibromoalkenes with alkenylzinc reagents, and exploits both substrate- and catalyst-controlled aspects of chemo-, regio- and stereoselectivity in the two C(sp²)–C(sp²) bond forming steps. The value of the new hydrocarbons in rapid structural complexity generation is demonstrated through their deployment in unprecedented diene- and triene-transmissive pericyclic reaction sequences.

Diene-Transmissive Enantioselective Diels-Alder Reactions and Sequences Involving Substituted Dendralenes

Readily available and stable substituted [3]dendralenes undergo highly chemo-, regio-, diastereo-, and enantioselective organocatalyzed Diels-Alder reactions with acrolein to form enantiomerically enriched cycloadducts. These monocycloadducts carry semicyclic dienes that undergo a second, substrate-controlled diastereoselective Diels-Alder reaction with a different dienophile to form 2-fold cycloadducts. Overall, annulated, functional group rich, chiral Δ¹⁽⁹⁾-octalin building blocks are accessed in one-pot operations that significantly extend the preparative value of diene-transmissive Diels-Alder sequences since they offer products of regio- and stereochemistry complementary to those generated from the parent, unsubstituted [3]dendralene.

Tetravinylallene

The first chemical synthesis of tetravinylallene (3,5-divinylhepta-1,3,4,6-tetraene) is reported. The final, key step of the synthesis involves a palladium-catalyzed, Negishi-type cross-coupling involving 1,5-transposition of a penta-2-en-4-yn-1-ol methanesulfonate. The unprecedented fundamental hydrocarbon is sufficiently stable to be purified by flash chromatography. A similar synthetic pathway grants access to the first substituted tetravinylallenes, which provide insights into the influence of substitution upon stability and reactivity. Tetravinylallenes are shown to break new ground in swift structural complexity creation, with three novel sequences reported.

Synthetic Entry to Polyfunctionalized Molecules through the [3+2]-Cycloaddition of Thiocarbonyl Ylides

Here we present a comprehensive study on the [3+2]-cycloaddition of thiocarbonyl ylides with a wide variety of alkenes and alkynes. The obtained dihydro- and tetrahydrothiophene products serve as exceptionally versatile intermediates providing access to thiophenes, dienes, dendralenes, and vic-quarternary carbon centers. The use of high-pressure conditions enables thermally unstable, sterically encumbered or moderately reactive substrates to undergo the cycloaddition under mild conditions, thereby increasing the yield by up to 58%. In addition, we showcase its utility by the formal syntheses of the pharmaceuticals NGB 4420 and tenilapine.

A concise approach to the tricyclic framework of longipinane- and ent-longipinane-type sesquiterpenoids

A general strategy for the synthesis of the common 6,6-dimethyltricyclic[5.4.0.0^2,8]undecane framework of longipinane- and ent-longipinane-type sesquiterpenoids has been successfully developed.

Broadly Applicable Stereoselective Syntheses of Serrulatane, Amphilectane Diterpenes, and Their Diastereoisomeric Congeners Using Asymmetric Hydrovinylation for Absolute Stereochemical Control

A stereogenic center, placed at an exocyclic location next to a chiral carbon in a ring to which it is attached, is a ubiquitous structural motif seen in many bioactive natural products, including di- and triterpenes and steroids. Installation of these centers has been a long-standing problem in organic chemistry. Few classes of compounds illustrate this problem better than serrulatanes and amphilectanes, which carry multiple methyl-bearing exocyclic chiral centers. Nickel-catalyzed asymmetric hydrovinylation (AHV) of vinylarenes and 1,3-dienes such as 1-vinylcycloalkenes provides an exceptionally facile way of introducing these chiral centers. This Article documents our efforts to demonstrate the generality of AHV to access not only the natural products but also their various diastereoisomeric derivatives. Key to success here is the availability of highly tunable phosphoramidite Ni(II) complexes useful for overcoming the inherent selectivity of the chiral intermediates. The yields for hydrovinylation (HV) reactions are excellent, and selectivities are in the range of 92-99% for the desired isomers. Discovery of novel, configurationally fluxional, yet sterically less demanding 2,2'-biphenol-derived phosphoramidite Ni complexes (fully characterized by X-ray) turned out to be critical for success in several HV reactions. We also report a less spectacular yet equally important role of solvents in a metal-ammonia reduction for the installation of a key benzylic chiral center. Starting with simple oxygenated styrene derivatives, we iteratively install the various exocyclic chiral centers present in typical serrulatane [e.g., a (+)- p-benzoquinone natural product, elisabethadione, nor-elisabethadione, helioporin D, a known advanced intermediate for the synthesis of colombiasin and elisapterosin] and amphilectane [e.g., A-F, G-J, and K,L pseudopterosins] derivatives. A concise table showing various synthetic approaches to these molecules is included in the Supporting Information. Our attempts to synthesize a hitherto elusive target, elisabethin A, led to a stereoselective, biomimetic route to pseudopterosin A-F aglycones.

Navigating the Chiral Pool in the Total Synthesis of Complex Terpene Natural Products

The pool of abundant chiral terpene building blocks (i.e., "chiral pool terpenes") has long served as a starting point for the chemical synthesis of complex natural products, including many terpenes themselves. As inexpensive and versatile starting materials, such compounds continue to influence modern synthetic chemistry. This review highlights 21st century terpene total syntheses which themselves use small, terpene-derived materials as building blocks. An outlook to the future of research in this area is highlighted as well.

General Approaches to Structurally Diverse Isocyanoditerpenes

Since their discovery in the 1970s, the striking architectures and the unusual isonitrile functional groups of the isocyanoterpenes have attracted the interest of many organic chemists. The more recent revelation of their potent in vitro antiplasmodial activity sparked new endeavors to synthesize members of this family of secondary metabolites. In this Synopsis, we discuss three distinct strategies that each address multiple structurally different members of the isocyanoterpenes, ending with some of our group's recent contributions in this area.

Tuning the Stability and the Reactivity of Substituted [3]Dendralenes for Quick Access to Diverse Copiously Functionalized Fused Polycycles with Step and Atom Economy

This is the first comprehensive study that details the synthesis of stable acyclic trisubstituted [3]dendralenes and deciphers their structural requisite for a successful diene transmissive Diels-Alder (DTDA) reaction by employing two different dienophiles and eventually generating a small repository of complex molecules, thus exemplifying how substituted [3]dendralenes could be deployed in diversity-oriented synthesis with high selectivities. A balance of reactivity and stability was struck by prudent selection of the position and nature of functional groups on these [3]dendralenes. Upon tandem Diels-Alder reactions with several symmetrical as well as unsymmetrical dienophiles, these dendralenes afforded diversity-oriented quick access to many polycyclic complex motifs possessing several functional groups and multiple stereogenic centers. Thus, the full potential of the dendralenes could be harnessed. The reactions proceeded under mild conditions with step and atom economy and were highly regio- and stereoselective besides being excellent yielding. The DTDA sequence resulted in the generation of four new carbon-carbon bonds, two new rings, and 3-7 stereogenic centers. The key feature of the method is that we could rapidly generate complexity along with functional and structural diversity from a trivial acyclic substrate with no stereogenic centers.

Stereocontrolled Synthesis of Kalihinol C

We report a concise chemical synthesis of kalihinol C via a possible biosynthetic intermediate, "protokalihinol", which was targeted as a scaffold en route to antiplasmodial analogs. High stereocontrol of the kalihinol framework relies on a heterodendralene cascade to establish the target stereotetrad. Common problems of regio- and chemoselectivity encountered in the kalihinol class are explained and solved.

An unexpected Lewis acid catalyzed Diels-Alder cycloaddition of aryl allenes and acrylates

An unexpected [4+2] cycloaddition of aryl allenes and simple acrylate derivatives is reported. This process functions well with a variety of allenes and acrylates to generate bi- and tricyclic dihydronaphthalene derivatives through a nonconventional bond disconnection.