Catalytic Enantioselective Total Synthesis of Hypocrolide A

Enantioselective Synthesis of the 1,3-Dienyl-5-Alkyl-6-Oxy Motif: Method Development and Total Synthesis

The 1,3-dienyl-5-alkyl-6-oxy motif is widely found in various types of bioactive natural products. However, present synthesis is mainly non-asymmetric which relied upon different olefination or transition metal-catalyzed cross-coupling reactions using enantioenriched precursors. Herein, based upon a newly developed enantioselective α-alkylation of conjugated polyenoic acids, a variety of 1,3-dienyl-5-alkyl-6-oxy motif (with E-configured internal olefin) was generated as the corresponding α-adducts in a highly enantioselective and diastereoselective manner. Utilizing 1,3-dienyl-5-alkyl-6-oxy motif as key intermediates, we further demonstrated their synthetic potential by expedient total syntheses of three types of natural products (glutarimide antibiotics, α-pyrone polyketides and Lupin alkaloids) within 4-7 steps.

Pd-Catalyzed Asymmetric Allylic Substitution Cascade of Substituted 4-Hydroxy-2H-pyrones with meso-Allyl Dicarbonates

An efficient Pd-catalyzed asymmetric allylic substitution cascade of 4-hydroxy-2H-pyrones with meso-allyl dicarbonates has been developed for the synthesis of kinetic chiral tetrahydro-1H-pyrano[4,3-b]benzofuran-1-one products in ≤87% yield and ≤99% ee. The protocol was achieved via a temperature-controlled kinetic control process, which has been illustrated by means of the experimental results and control experiments. The reaction could be conducted on a gram scale, and the resulting product allows for several transformations.

Enantioselective Synthesis of Indanes with a Quaternary Stereocenter via Diastereoselective C(sp3)-H Functionalization

A practical synthesis of enantioenriched indane derivatives with quaternary stereocenters was developed via sequential enantioselective reduction and C-H functionalization. Good to excellent enantioselectivity could be achieved by either the CuH-catalyzed asymmetric reduction or the Corey-Bakshi-Shibata (CBS) reduction of indanone derivatives. The subsequent diastereospecific and regioselective rhodium-catalyzed silylation of the methyl C-H bond led to indane derivatives with quaternary centers. This strategy was further applied in syntheses of (nor)illudalane and botryane sesquiterpenoids.

Arthrinins E-G, Three Botryane Sesquiterpenoids from the Plant Endophytic Fungus Arthrinium sp. HS66

Arthrinins E-G (1-3), three new sesquiterpenoids possessing non-isoprenoid botryane skeleton, were isolated from the fermentation of an endophytic fungus named Arthrinium sp. HS66 which colonized in the stems of Isodon xerophilus. Their structures were determined by extensive spectroscopic methods. Furthermore, the structure of 1 was unambiguously confirmed by X-ray diffraction, while those of 2 and 3 were verified through quantum chemical calculation of NMR data and ECD spectra.

Total Synthesis of Nominal ent-Chlorabietol B

The nominal enantiomer of chlorabietol B was regio- and stereoselectively synthesized from (-)-abietic acid in 13 steps. Key features of the synthesis involved an oxidative [3+2] cycloaddition to install the dihydrobenzofuran moiety and an Aldol reaction, followed by elimination and reduction steps to introduce the long chain with three cis double bonds. However, obvious differences in the NMR spectra of the synthetic and natural samples suggested that the proposed structure of chlorabietol B should be revised carefully.

Development and Elucidation of a Pd-Based Cyclization-Oxygenation Sequence for Natural Product Synthesis

Pd-catalyzed sequences involving oxidative addition, cyclization, and termination through intermolecular nucleophile capture have tremendous utility. Indeed, they can generate a plethora of different polycyclic structures possessing a diverse range of functionality. However, one area of deficiency for Pd0 /PdII variants is the ability to conclude them with oxygen-based species. Inspired by the recent discovery of one such reaction in the course of a total synthesis program, we delineate herein that it has significant strength, both in terms of substrate scope as well as the terminating oxygen nucleophile. As a result, the reaction proved critical in achieving total syntheses of two oxygenated natural products, one of which was prone to over-oxidation. Finally, a mechanistic proposal that accounts for its success is provided.

Bio-inspired enantioselective total syntheses of (-)-viminalins A, B, H, I, and N and structural reassignment of (-)-viminalin M

Bio-inspired enantioselective total syntheses of (-)-viminalins A, B, H, I, and N, isolated from the Myrtaceae family, were accomplished in a convergent fashion in 5, 5, 1, 1, and 3 steps, respectively. A highly regio- and diastereoselective oxidative [3 + 2] cycloaddition reaction of acylphloroglucinols with α-phellandrene, diastereoselective modified Friedel-Crafts reaction of acylphloroglucinols with piperetol, and stereoselective epoxidation of extremely hindered β-face were described as key reactions.

Asymmetric synthesis of the tetracyclic core of bufogargarizin C by an intramolecular [5 + 2] cycloaddition

A concise asymmetric synthesis of the synthetically challenging 7/5/6/5-tetracyclic core of bufogargarizin C by a unique intramolecular [5 + 2] cycloaddition was reported.

Synthetic Study toward the Total Synthesis of Taxezopidines A and B

A concise synthetic approach to construct the [6,8,6]-tricyclic core of taxezopidines A and B, which contains a synthetically challenging bridged bicyclo[5.3.1]undecane ring system bearing most of the desired functionalized groups and stereocenters, has been established. This approach features a diastereoselective type II intramolecular Diels-Alder furan reaction. The stereochemistry of the acetoxy group at the allylic position of the dienophile alkene group, such as in 6a, was found to be critical for achieving the desired highly diastereoselective outcome.

Asymmetric Total Synthesis of Cyclocitrinol

The first and asymmetric total synthesis of cyclocitrinol, an unusual C25 steroid, has been accomplished in a linear sequence of 18 steps from commercially available compound 11. The synthetically challenging bicyclo[4.4.1] A/B ring system with a strained bridgehead (anti-Bredt) double bond of cyclocitrinol was constructed efficiently and diastereoselectively via a type II intramolecular [5 + 2] cycloaddition.

Catalytic asymmetric total syntheses of myrtucommuacetalone, myrtucommuacetalone B, and callistrilones A, C, D and E

Herein, we describe a concise catalytic approach to the first asymmetric total syntheses of myrtucommuacetalone, myrtucommuacetalone B, and callistrilones A, C, D and E. The syntheses proceed in only 5-7 steps from the readily available compound 11, without the need for protecting groups. Key features of the syntheses include a unique organocatalytic asymmetric Friedel-Crafts-type Michael addition with high enantioselectivity and a broad substrate scope, a novel Michael-ketalization-annulation cascade reaction, and an oxidative [3 + 2] cycloaddition. Furthermore, the new compound 7 exhibited potent antibacterial activities against several multidrug-resistant strains (MRSA, VISA and VRE), and showed greater potency than vancomycin.

Asymmetric total syntheses of callistrilones B, G and J

A highly concise approach for the first asymmetric and gram-scale total syntheses of callistrilones B, G and J is reported.