An enantioselective total synthesis of aspergillides A and B

An enantioselective total synthesis of aspergillides A and B has been accomplished on the basis of a unified synthetic strategy that exploits stereodivergent intramolecular oxa-conjugate cyclization and Yamaguchi macrolactonization.     

First enantioselective total synthesis of penicimarin B,aspergillumarins A and B

A convergent enantioselective synthesis of penicimarin B, aspergillumarin A and B has been reported using Brown’s allylation, DeBrabander–Bhattacharjee lactonization and Grubbs cross coupling metathesis. During this synthesis we have standardized the conditions for DeBrabande–Bhattacharjee lactonization to obtain excellent yield (>90%).     

The first enantioselective total synthesis of(+)-preussin B and an improved synthesis of(+)-preussin by step-economical methods

The first enantioselective total synthesis of(+)-preussin B and an improved synthesis of the antifungal alkaloid(+)-preussin are described. Our approach relied on the four step-economical synthetic methods developed in our laboratory:(1) the cis-diastereoselective reductive dehydroxylation of hemiaminals;(2) the direct amide/lactam reductive alkylation;(3) the one-pot N,O-bisdebenzylation-N-methylation; and(4) the one-step synthesis of malimide from malic acid. Both total syntheses are quite concise, which have been achieved in six steps, and gave overall yields of 25.7% and 27.6%, respectively.     

An expeditious enantioselective total synthesis of valilactone

The title compound was synthesized through an expeditious route using Crimmins aldolization to establish the two key stereogenic centers and a hydroxyl group activation (HGA) protocol to construct the anti alpha,beta-disubstituted beta-lactone from the corresponding syn aldol.     

An enantioselective total synthesis of (+)-geissoschizine

[formula: see text] A concise asymmetric synthesis of the indole alkaloid (+)-geissoschizine (1) has been completed. The synthesis features the highly diastereoselective vinylogous Mannich reaction of 3 with 4 to give 5, which is elaborated into the key tetracyclic intermediate 7 in two steps. Following the stereoselective introduction of the ethylidene moiety to give 9, reduction of the lactam and radical decarboxylation via an acyl selenide gave 12, which was converted into (+)-geissoschizine by formylation. The synthesis requires only 11 chemical operations and proceeds in an overall yield of 17%.     

Highly enantioselective total synthesis of (+)-isonitramine

A new efficient enantioselective synthetic method of (+)-isonitramine is reported. (+)-Isonitramine was obtained in 12 steps (98% ee and 43% overall yield) from δ-valerolactam via enantioselective phase-transfer catalytic alkylation, Dieckman condensation, and diastereoselective reduction as key steps.     

Synthetic studies on cyathins: enantioselective total synthesis of (+)-allocyathin B2

[reaction: see text] The enantioselective total synthesis of (+)-allocyathin B(2) has been achieved. Our approach features a convergent enantioselective construction of the 5-6-7 tricyclic core system using the originally developed chiral building blocks via asymmetric catalysis, the intramolecular aldol reaction in high yield, successful samarium diiodide-mediated ring expansion, and a newly developed double-bond installation method.     

An enantioselective total synthesis of pinnaic acid

An enantioselective and convergent total synthesis of marine natural product pinnaic acid has been achieved. Our general synthetic approach is featured with an asymmetric hydrogenation of racemic γ-keto ester 3, a diastereoselective methylation on the α-methylene of the (1R,5R)-lactone 4, and a diastereoselective Michael addition of the tertiary nitro cyclopentane. The central azaspiro[4.5]decane was constructed utilizing reductive cyclization of the δ-nitroketone followed by highly stereoselective reduction of the cyclic imine with NaBH₄. Ultimately, successive use of triethyl-2-phosphonopropionate and Heathcock's phosphorane 18 to elaborate C5 and C13 side chains completed the total synthesis of pinnaic acid.     

An enantioselective total synthesis of (+)-aigialospirol

A concise and enantioselective total synthesis of (+)-aigialospirol is described here, featuring the first complex natural product synthesis that employs a cyclic ketal-tethered ring-closing metathesis strategy and an unexpected stereoselective epimerization of a benzylic hydroxyl group. The 15-step synthetic sequence illustrates the proof-of-concept that such an approach can be competitive with the classical spiroketal formation in the natural product synthesis.     

Catalytic enantioselective synthesis of adociacetylene B

A catalytic enantioselective total synthesis of adociacetylene B (2) in five steps is reported. The efficiency of this synthesis was enabled by an asymmetric zinc alkynylation catalyzed by the proline-derived ligand (1).     

A practical enantioselective total synthesis of the bengamides B,E, and Z

[reaction: see text] A practical total synthesis of Bengamides B, E, and Z from a common polyol intermediate is described. Consecutive aldol condensations afford a protected polyol thioester side chain suitable for coupling to the Bengamides. A novel chiral phase transfer catalyzed enantioselective alkylation affords the more highly functionalized amino caprolactams required for Bengamides B and Z. Use of the 2-naphthylmethyl ether protecting group, compatible with the boron Lewis acids required for enantioselective aldol condensation, allows direct access to Bengamide B.     

An intramolecular Diels-Alder approach to the eunicelins: enantioselective total synthesis of ophirin B

The enantioselective synthesis of the eunicellin ophirin B has been completed. A ring-closing metathesis provides efficient access to the oxonene ring, and a highly diastereoselective intramolecular Diels-Alder reaction results in the formation of the hydrobenzofuran portion of the molecule.     

The total synthesis of strobilurin B

A new regio- and stereocontrolled total synthesis of the antibiotic strobilurin B is performed in nine steps in 5.5% overall yield.     

Catalytic enantioselective total synthesis of (+)-torrubiellone C

Silyl-protected (R)-methyl 2-(hydroxymethyl)butanoate was obtained by an enantioselective Ir-catalyzed hydrogenation in high yield and selectivity. Elaboration of this building block via Takai and Stille reactions gave a protected hydroxy polyene chain, which was coupled to a 5-hydroxyphenyl-4-hydroxy-2-pyridone derivative by a modified Horner-Wadsworth-Emmons reaction. Deprotection gave synthetic (+)-torrubiellone C, which led to the assignment of the configuration of the natural product as (R).     

A highly enantioselective total synthesis of (+)-goniodiol

A high-yielding enantioselective total synthesis of the bioactive styryllactone (+)-goniodiol has been realised, starting from readily available (S)-glycidol. A key step is an oxygen-to-carbon rearrangement of a silyl enol ether linked via an anomeric centre, facilitating the rapid and diastereoselective construction of this functionalised system.     

The total synthesis of pantocin B

[reaction: see text] Pantocin B, an unusual antibiotic produced by Erwinia herbicola, effectively controls E. amylovora, the pathogen causing the plant disease fire blight. A total synthesis of pantocin B from L-alanine, glycine, and L-malic acid is reported.     

An enantioselective total synthesis of (+)-ricciocarpin A

[reaction: see text] Starting from 4,4-dimethyl-2-cyclohexenone, an efficient total synthesis of ricciocarpin A (1) in natural form has been accomplished.