Enantioselective Total Synthesis of (+)-Homochelidonine by a PdII-Catalyzed Asymmetric Ring-Opening Reaction of ameso-Azabicyclic Alkene with an Aryl Boronic Acid

Selective access to dihydrophenanthridines and phenanthridinones via cyclisation of aryl amines onto N-tethered arynes

5,6-Dihydrophenanthridines are prepared from aryl amines via intramolecular addition to N-tethered arynes under mild conditions. A new o-silylaryl triflate precursor was developed to increase reactivity and enable electron-rich and electron-poor aryl amines to undergo cyclisation. A complete switch in product selectivity occurs when the reaction is conducted in air, affording the corresponding phenanthridin-6(5H)-one as the sole product under otherwise identical reaction conditions.

Iron Trichloride-Mediated Cascade Reaction of Aminosugar Derivatives for the Synthesis of Fused Tetrahydroisoquinoline-Tetrahydrofuran Systems

A method to obtain tetrahydroisoquinolines (THIQs) fused to tetrahydrofuran rings from aminosugar derivatives has been developed. The procedure relies on a key deprotection of benzyl ethers followed by a double-cyclization sequence, using FeCl₃ as the sole reagent. This tandem reaction affords the construction of novel fused polycyclic heterocycles with total stereochemical control.

Synthesis of Pyrrolidine- and γ-Lactam-Containing Natural Products and Related Compounds from Pyrrole Scaffolds

Polycyclic alkaloid natural products featuring pyrrolidine and pyrrolidinone motifs remain enduring targets of total synthesis endeavors. Pyrrole and its derivatives have been exploited to access many such frameworks, including alkaloids belonging to the Aspidosperma, Stemona, and batzelladine families. In this article, a selection of exemplars that highlight the utility of pyrrole-based approaches to facilitate total syntheses of pyrrolidine- and pyrrolidinone-containing alkaloids and related molecules are showcased.

Iron-catalysed enantioselective carbometalation of azabicycloalkenes

The first enantioselective carbometalation reaction of azabicycloalkenes has been achieved by iron catalysis to in situ form optically active organozinc intermediates, which are amenable to further synthetic elaborations. The observed chiral induction, along with the DFT and XAS analyses, reveals the direct coordination of the chiral phosphine ligand to the iron centre during the carbon-carbon and carbon-metal bond forming step. This new class of iron-catalysed asymmetric reaction will contribute to the synthesis and production of bioactive molecules.

Catalytic asymmetric transformations of oxa- and azabicyclic alkenes

This review provides an overview of the fundamental concepts and recent developments in a wide range of enantioselective transformations involving oxa- and azabicyclic alkenes.

Asymmetric Synthesis of 1,2-Dihydronaphthalene-1-ols via Copper-Catalyzed Intramolecular Reductive Cyclization

We describe a copper-catalyzed intramolecular reductive cyclization of easily accessible benz-tethered 1,3-dienes containing a ketone moiety. This process provided biologically active 1,2-dihydronaphthalene-1-ol derivatives in good yields with excellent enantio- and diastereoselectivity. Mechanistic investigations using density functional theory revealed that (Z)- and (E)-allylcopper intermediates formed in situ from the diene and copper catalyst undergo isomerization and selective intramolecular allylation of the (E)-allylcopper form of the major product through a six-membered boatlike transition state. The resulting products were further transformed to fully saturated naphthalene-1-ols by reactions of the olefin moiety.

Three-Component Cycloaddition To Synthesize Aziridines and 1,2,3-Triazolines

An efficient three-component cycloaddition of oxa(aza)bicyclic alkenes/norbornene in the presence of NaN₃ and arylsulfonyl chlorides was developed, affording the corresponding aziridine products in good yields (up to 82%) with moderate to good endo/exo selectivities (up to >99:1 endo/exo). Further studies showed that the cycloaddition of oxa(aza)bicyclic alkenes in the presence of NaN₃ and chloroalkanes could afford the exo-cycloadduct 1,2,3-triazolines in good to excellent yields (up to 95%). Compared with the existing methodologies, the current protocol demands very simple and mild reaction conditions and is a metal-free catalyzed reaction. In addition, a plausible mechanism for the cycloaddition reaction was also proposed.

Nickel-catalyzed syn-stereocontrolled ring-opening of oxa- and azabicyclic alkenes with dialkylzinc reagents

A new efficient nickel-catalyzed syn-stereocontrolled ring-opening of oxa(aza)bicyclic alkenes with dialkylzinc reagents was developed.

Ir-Catalyzed ring-opening of oxa(aza)benzonorbornadienes with water or alcohols

A highly efficient Ir-catalyzed ring-opening reaction of oxa(aza)benzonorbornadienes with water was firstly developed, which afforded a mild access to substituted dihydronaphthalene products with excellent yields (up to 99%) within 30 min.

Diels-Alder cycloadditions of N-arylpyrroles via aryne intermediates using diaryliodonium salts

With a strategy of the formation of benzynes by using diaryliodonium salts, a cycloaddition reaction of N-arylpyrroles with benzynes was reported. A wide range of bridge-ring amines with various substituents have been synthesized in moderate to excellent yields (35-96%). Furthermore, with a catalytic amount of TsOH·H₂O, these amines can be converted into the corresponding N-phenylamine derivatives easily, which are potentially useful in photosensitive dyes.

Aryne-based strategy in the total synthesis of naturally occurring polycyclic compounds

This review has outlined the strategies and tactics of using arynes in the total syntheses of polycyclic natural products.

Cobalt-catalyzed asymmetric reactions of heterobicyclic alkenes with in situ generated organozinc halides

A general strategy for the asymmetric allylation and benzylation of heterobicyclic alkenes is described by employing in situ generated organozinc halides.

Palladium-catalyzed enantioselective C(sp2)–H arylation of ferrocenyl ketones enabled by a chiral transient directing group

A carboxylate-assisted palladium-catalyzed enantioselective C(sp²)–H arylation of ferrocenyl ketones is achieved through utilizing catalyticl-tert-leucine as a chiral transient directing group.

Formal synthesis of chelamidine alkaloids and their derivatives

A concise two-step operation of α-amination of aldehydes and subsequent Friedel–Crafts/Prins-type cyclization towards accessing tetrahydrobenzo[c]phenanthridine and related structures was developed. In addition, the effectiveness of this protocol was also demonstrated in the formal synthesis of homochelidonine and chelamidine.

Palladium-Catalyzed Dearomative syn-1,4-Carboamination

A dearomative 1,4-carboamination of arenes has been achieved using arenophile cycloaddition and subsequent palladium-catalyzed substitution with nonstabilized lithium enolates. This protocol delivers products with exclusive syn-1,4-selectivity and can be also conducted in an asymmetric fashion. The method allows rapid dearomative difunctionalization of simple aromatic compounds into functional small molecules amenable to further diversification.

Platinum-catalyzed syn-stereocontrolled ring-opening of oxabicyclic alkenes with sodium arylsulfinates

A new efficient platinum-catalyzed ring-opening reaction of oxabicyclic alkenes with a wide range of sodium arylsulfinates was developed.

Asymmetric Synthesis of Isoquinoline Alkaloids: 2004-2015

In the past decade, the asymmetric synthesis of chiral nonracemic isoquinoline alkaloids, a family of natural products showing a wide range of structural diversity and biological and pharmaceutical activity, has been based either on continuation or improvement of known traditional methods or on new, recently developed, strategies. Both diastereoselective and enantioselective catalytic methods have been applied. This review describes the stereochemically modified traditional syntheses (the Pictet-Spengler, the Bischler-Napieralski, and the Pomeranz-Fritsch-Bobbitt) along with strategies based on closing of the nitrogen-containing ring B of the isoquinoline core by the formation of bonds between C₁-N₂, N₂-C₃, C₁-N₂/N₂-C₃, and C₁-N₂/C₄-C_4a atoms. Methods involving introduction of substituents at the C1 carbon of isoquinoline core along with syntheses applying various biocatalytic techniques have also been reviewed.

Type 1 Ring-Opening Reactions of Cyclopropanated 7-Azabenzonorbornadienes with Organocuprates

The first nucleophilic ring-opening reactions of cyclopropanated 7-azabenzonorbornadienes have been achieved using organocuprates. Tricyclic or tetracyclic γ-lactams were obtained as the sole product in good yields of up to 98% when alkoxycarbonyl groups occupied the N-substituent position. Successful conversions to lactams were observed for primary, secondary, tertiary, and aromatic nucleophiles, as well as for a variety of substrates functionalized on the benzene ring. A possible mechanism for these transformations is discussed.

Concise enantiospecific total synthesis of tubingensin A

We report the enantiospecific total synthesis of (+)-tubingensin A. Our synthesis features an aryne cyclization to efficiently introduce the vicinal quaternary stereocenters of the natural product and proceeds in only nine steps (longest linear sequence) from known compounds.

Total syntheses of chelidonine and norchelidonine via an enamide-benzyne-[2 + 2] cycloaddition cascade

Total syntheses of chelidonine and norchelidonine featuring an enamide-benzyne-[2 + 2] cycloaddition initiated cascade is described. The cascade includes a pericyclic ring-opening and intramolecular Diels-Alder reaction.

The trisubstituted-triazole approach to extended functional naphthalocyanines

Recently, a novel modular approach to octatriazole-derived phthalocyanines (Pcs; 1) was developed and optimized in our group; herein, the pool of the functional Pc materials was expanded for an additional candidate (2), a fused derivative of 1. Compared with 1, the aromaticity in 2 is extended by an additional four benzene and eight triazole rings and, in addition, the triazole units and the Pc core co-create four functional, in-plane cavities. Various methods to link the unsubstituted carbon atoms of the neighboring triazoles in 1 to afford atomically flat naphthalocyanine (Nc) analogs (2), containing eight fused triazole moieties, were studied. Several synthetic routes were designed, among them the trisubstituted-triazole approach, which was found to be the most suitable route. The crucial steps of this approach, the copper-catalyzed azide-haloalkyne cycloaddition and the intramolecular homocoupling reactions, were first studied on a model system; subsequently, this methodology was applied in the synthesis of the desired Nc 2. The increased core size and the π-electron deficient structure predict this class of Ncs to possess very strong aggregation properties. Moreover, owing to the presence of four tridentate half-cavities, the final properties of the molecule or the assembly can, in principle, be further tuned by doping with metals or guest molecules.

Reactivity and selectivity in hydrovinylation of strained alkenes

The scope of Ni(II)-catalyzed hydrovinylation has been extended to strained alkenes such as heterobicyclic [2.2.1]heptanes and cylobutenes. Reactions involving the heterobicyclic compounds are rare examples for this class of compounds where the metal-catalyzed C-C bond-forming reactions proceed without a concomitant ring-opening process. While the enantioselectivity in these systems remains modest, hydrovinylation of endo-5,6--bis-benzyloxymethylbicyclo[2.2.1]hept-2-ene gives excellent yield (>90%) of the product with one of the highest enantioselectivities (95-99% ee) reported for a C-C bond-forming reaction of norbornenes.