Weijun Yao

Asymmetric Synthesis of Spiropyrazolones through Phosphine‐Catalyzed [4+1] Annulation

An enantioselective synthesis of spiropyrazolones from allenoate-derived MBH acetates and pyrazolones through a phosphine-mediated [4+1] annulation process has been developed. Spiropyrazolones were readily prepared in good chemical yields and good to high enantioselectivities. This is the first asymmetric example in which α-substituted allenoates were utilized as a C4 synthon for phosphine-catalyzed [4+1] annulation.

Highly enantioselective synthesis of 3,4-dihydropyrans through a phosphine-catalyzed [4+2] annulation of allenones and β,γ-unsaturated α-keto esters.

A phosphine-catalyzed novel [4+2] annulation process was devised employing allene ketones as C2 synthons and β,γ-unsaturated α-keto esters as C4 synthons. In the presence of an L-threonine-derived bifunctional phosphine, 3,4-dihydropyrans were obtained in high yields and with virtually perfect enantioselectivities. The synthetic value of the dihydropyran motif was demonstrated by a concise preparation of an anti-hypercholesterolemic agent.

Asymmetric construction of functionalized bicyclic imides via [3 + 2] annulation of MBH carbonates catalyzed by dipeptide-based phosphines.

A highly enantioselective [3 + 2] annulation of MBH carbonates and maleimides catalyzed by chiral phosphines has been developed. In the presence of 5 mol % of L-Thr-L-Val-derived phosphine 6, functionalized bicyclic imides were prepared in excellent yields, and with high diastereoselectivities and nearly perfect enantioselectivities.

Phosphine‐Catalyzed Enantioselective γ‐Addition of 3‐Substituted Oxindoles to 2,3‐Butadienoates and 2‐Butynoates: Use of Prochiral Nucleophiles

The first phosphine-catalyzed enantioselective γ-addition with prochiral nucleophiles and 2,3-butadienoates as the reaction partners has been developed. Both 3-alkyl- and 3-aryl-substituted oxindoles could be employed in this process, which is catalyzed by a chiral phosphine that is derived from an amino acid, thus affording oxindoles that bear an all-carbon quaternary center at the 3-position in high yields and excellent enantioselectivity. The synthetic value of these γ-addition products was demonstrated by the formal total synthesis of two natural products and by the preparation of biologically relevant molecules and structural scaffolds.

Enantioselective construction of 3-hydroxy oxindoles via decarboxylative addition of β-ketoacids to isatins.

The first highly enantioselective decarboxylative addition of β-ketoacids to isatins mediated by a bifunctional tertiary amine-thiourea catalyst has been developed, allowing facile synthesis of biologically important 3-hydroxy oxindoles in good yields and excellent enantioselectivities. The method reported represents a valuable approach of utilizing β-ketoacids as synthetic equivalents of aryl/alkyl methyl ketone enolates.

Enantioselective [4 + 2]-Annulation of Oxadienes and Allenones Catalyzed by an Amino Acid Derived Phosphine: Synthesis of Functionalized Dihydropyrans.

An enantioselective [4 + 2]-annulation process between cyano-activated oxadienes and allenones is developed. An l-valine-derived phosphine was efficient in catalyzing the reaction, and a wide range of highly functionalized dihydropyrans were prepared in high yields and with excellent enantioselectivities.

A facile approach for the asymmetric synthesis of oxindoles with a 3-sulfenyl-substituted quaternary stereocenter.

With the employment of a threonine-incorporating multifunctional catalyst 9, Michael addition of 3-sulfenyloxindoles to nitroolefins proceeded stereoselectively, leading to the formation of oxindoles with a 3-sulfenyl-substituted quaternary center in excellent yields, and with high diastereoselectivities and excellent enantioselectivities.

Enantioselective desymmetrization of cyclohexadienones via an intramolecular Rauhut–Currier reaction of allenoates

The Rauhut–Currier (RC) reaction represents an efficient method for the construction of carbon–carbon bond in organic synthesis. However, the RC reactions involving allenoate substrates are very rare, and in particular, asymmetric intramolecular RC reaction of allenoates is yet to be discovered. Here, we show that the intramolecular RC reaction proceeds smoothly in the presence of 1 mol% β-ICD, and bicyclic lactones are obtained in high yields and with excellent enantiomeric excesses. With the employment of γ-substituted allenoates as racemic precursors, a novel dynamic kinetic resolution of allenes via RC reaction is observed, which allows for facile synthesis of highly enantiomerically enriched allenes.

Enantioselective Phosphine-Catalyzed Formal [4+4] Annulation of α,β-Unsaturated Imines and Allene Ketones: Construction of Eight-Membered Rings

The first highly enantioselective phosphine-catalyzed formal [4+4] annulation has been developed. In the presence of amino-acid-derived phosphines, the unprecedented [4+4] annulations between benzofuran/indole-derived α,β-unsaturated imines and allene ketones proceeded smoothly, thus affording azocines, bearing either a benzofuran or an indole moiety, in excellent yields and with nearly perfect enantioselectivities (≥98 % ee in most cases). This work marks the first efficient asymmetric construction of optically enriched eight-membered rings by phosphine catalysis.

Phosphine-Catalyzed Enantioselective [4 + 2] Annulation of o-Quinone Methides with Allene Ketones

A phosphine-catalyzed highly enantioselective [4 + 2] annulation between ortho-quinone methides and allene ketones has been developed. The reported method led to the formation of chromane derivatives in high yields and excellent enantioselectivity. This is the first time that ortho-quinone methides are employed in phosphine-mediated cyclization reactions.