Convergent Synthesis of Dihydropyrans from Catalytic Three-Component Reactions of Vinylcyclopropanes, Diazoesters, and Diphenyl Sulfoxide.

A novel Rh(I)/La(III) cocatalytic three-component reaction of vinylcyclopropanes, diazoesters, and diphenyl sulfoxide has been developed. The reaction gives polysubstituted dihydropyrans as the reaction products. Mechanistic studies indicate that isomerization of vinylcyclopropanes gives conjugated dienes, which then undergo [4 + 2]-cycloaddition with vicinal tricarbonyl compounds generated by oxygen atom transfer from diphenyl sulfoxide to diazoesters.

Rhodium-Catalyzed ortho-Selective Carbene C-H Insertion of Unprotected Phenols Directed by a Transient Oxonium Ylide Intermediate.

ortho-Selective carbene C-H insertion of unprotected phenols is achieved with dimethyl diazomalonate under the catalysis of [Rh(COD)Cl]2. After the C-H insertion, subsequent cyclization and electrophilic addition of another carbene molecule affords tris-carboxylate-substituted 2-benzofuranones as the final reaction products. The enantioselective variant has been developed with the use of chiral diene ligands. Mechanistic experiments indicate that a transient oxonium ylide directing group might be responsible for the regiocontrol at the C-H activation step.

Catalytic Intermolecular Coupling of Rhodacyclopentanones with Alcohols Enabled by Dual Directing Strategy.

A catalytic carbonylative ring-opening and functionalization reaction of poorly activated cyclopropanes has been developed. The key achievement of this work is the accomplishment of an unprecedented effective intermolecular trapping of the rhodacyclopentanone intermediate, which is derived from rhodium-mediated carbonylative insertion of poorly activated cyclopropanes, by an external reactant. The success of this development hinges upon the use of a dual directing strategy.

B(C6 F5 )3 -Catalyzed Ring Opening and Isomerization of Unactivated Cyclopropanes.

Catalytic amounts of B(C6 F5 )3 promote the ring opening and subsequent isomerization of a series of unactivated cyclopropanes to afford terminal olefins in good yields when a hydrosilane and 2,6-dibromopyridine are employed as additives.