PIDA-Promoted/HFIP-Controlled Dearomative Spirocyclization of Phenolic Ketones via a Spirocyclohexadienone-Oxocarbenium Cation Species.

A phenyliodine(III) diacetate-promoted/1,1,1,3,3,3-hexafluoroisopropanol-controlled dearomative spirocyclization of phenolic ketones was reported, providing two libraries of structurally interesting scaffolds, spirocyclohexadienonic ketals and their acetoxylated counterparts, in moderate to excellent yields under mild conditions. Control experiments unravel that the reaction proceeds through a spirocyclohexadienone-oxocarbenium cation species. In addition, an in situ-generated hypervalent iodine(III)-catalyzed version, as well as the late-stage transformation of products via conjugate additions, was also realized.

Enantioselective Synthesis of α-Aryl-ß-Aminocyclopropane Carboxylic Acid Derivatives via Rh(II)-Catalyzed Cyclopropanation of Vinylsulfonamides with α-Aryldiazoesters.

The reaction of vinylsulfonamides with donor-acceptor carbenes derived from α-aryldiazoesters, catalyzed by the tert-butyl glycine-derived dirhodium complex Rh2(S-4-Br-NTTL)4, has been reported. This method provides a variety of α-aryl-ß-aminocyclopropane carboxylic acid derivatives bearing one quaternary carbon stereogenic center vicinal to the amino-substituted carbon in high yields with excellent diastereo- and enantioselectivities. Vinylsulfonamides showed complementary advantages over the well-developed vinylamides or vinylcarbamates for this Rh(II)-catalyzed cyclopropanation strategy. Moreover, these conformationally restricted α-aryl-ß-aminocyclopropyl carboxylic acid derivatives can be readily incorporated into dipeptides.

Copper-Catalyzed Cycloadditions of Diazo Compounds with Imidazolidines/Hexahydropyrimidines for the Syntheses of N-Heterocycles.

Reported herein are the unprecedented copper-catalyzed formal [n + 1]/[n + 3] (n = 5, 6) cycloadditions of diazo compounds with imidazolidines/hexahydropyrimidines, thus providing a general, economical, and efficient route to construct different sized (six- to nine-membered) diaza-heterocycles in moderate to excellent yields under mild reaction conditions. This strategy features the use of copper catalyst to accomplish such diverse annulations and the utilization of imidazolidines/hexahydropyrimidines as stable 1,5-/1,6-dipoles.

Unexpected Copper-Catalyzed Cascade Reaction of 1,6-Enynes with Sulfoxonium Ylides.

An unprecedented copper-catalyzed cascade reaction of 1,6-enynes with sulfoxonium ylides is reported, providing a series of structurally intriguing 2,3-disubstituted indolines bearing a conjugated dienone functionality at the 3-position in moderate to excellent yields with good chemo-, regio-, and diastereoselectivities under mild reaction conditions. Importantly, sulfoxonium-ylide-derived copper-carbene herein exhibits quite different reactivity from that of diazo copper-carbene. A rational mechanism, an initial ammonium ylide rather than allene formation, is proposed.