Synthesis of Spirooxindole-1,2-oxazinan-5-ones through 2,2,2-Trifluoroethanol Promoted [3 + 3] Cycloaddition of N-Vinyl Oxindole Nitrones and Oxyallyl Cations

A variety of spirooxindole-1,2-oxazinan-5-one derivatives were prepared in moderate to excellent yields through 2,2,2-trifluoroethanol (TFE)-promoted [3 + 3] cycloaddition of N-vinyl oxindole nitrones with oxyallyl cations generated from α-tosyloxy ketones under mild reaction conditions. Mechanistic studies revealed that [3 + 3] cycloaddition might involve two possible reaction pathways, including direct [3 + 3] cycloaddition of N-vinyl oxindole ntirones with oxyallyl cations, or the addition of TFE to N-vinyl oxindole nitrones, sequential addition to oxyallyl cations, elimination, and cyclization. The present method features mild reaction conditions, broad substrate scope, good functional group tolerance, easy gram scalable preparation, and new applications of TFE.

Preparation of Alkyl Di(p-tolyl)sulfonium Salts and Their Application in Metal-Free C(sp3)-C(sp3) and C(sp3)-C(sp2) Bond Formations

Alkyldiarylsulfonium salts were synthesized by a combination of active sulfonium species, prepared through the activation of diarylsulfoxide, and alkyl nucleophiles. The isolated sulfonium salts were subjected to the allylation and cyclopropanation of the active methylene compounds and metal-free C(sp³)-C(sp²) couplings via oxyallyl cation intermediates under mild conditions. The series of reactions included an umpolung strategy for the coupling of alkyl nucleophiles and metal-free C-C bond formation using sulfonium salts.

Direct Use of Phosphonium Salts for Alkylation of p-Quinols: Formal α-Arylation of Carbonyls via a 5-Membered Betaine-Type Intermediate

Unlike phosphonium ylides used extensively for C═C bond formation, herein we disclose the direct use of phosphonium salts for site-selective alkylation to p-quinols via a 5-membered betaine-type intermediate. This strategy provides a novel and general approach for the synthesis of α-(m-aminoaryl) esters, amides and ketones under ambient conditions. The reaction proceeds through in situ generation of P-ylide, alkylation and aromatization. Reaction is highly compatible with diverse functional phosphonium salts and amines.

Ring Contraction of Tropylium Ions into Benzenoid Derivatives

We report a method to convert substituted tropylium ions into benzenoid derivatives.

Catalytic Asymmetric (3 + 3) Cycloaddition of Oxyallyl Zwitterions with α-Diazomethylphosphonates

The unique structure of oxyallyls represents a significant challenge for their catalytic asymmetric applications. Herein, an unprecedented chiral imidodiphosphoric acid-catalytic enantioselective (3 + 3) cycloaddition between oxyallyl zwitterions generated in situ from α-haloketones and α-diazomethylphosphonates was developed. Pharmaceutically interesting chiral pyridazine-4(1H)-ones were obtained in up to 98% yields with excellent stereoselectivities (up to 99% ee, > 99:1 dr).

Formal Enone α-Arylation via I(III)-Mediated Aryl Migration/Elimination

A formal enone α-arylation is described. This metal-free transformation relies on the I(III)-mediated skeletal reorganization of silyl enol ethers and features mild conditions, good yields, and high stereoselectivities for β-substituted enones.