Allylboron and Boron Enolate Chemistry. Stereodirected Synthesis with Organoboranes. Berlin: Springer Berlin Heidelberg; 1995. pp. 260-328. [DOI: 10.1007/978-3-642-79709-5_7]

One-Carbon Homologation of Knoevenagel Adducts: Enantioselective Access to Benzhydryl Derivatives

A one-carbon homologation of Knoevenagel adducts enabling the insertion of a CHAr fragment is reported. The strategy involves a sulfur ylide mediated cyclopropanation followed by the rearrangement of cyclopropanes and enables the synthesis of a series of benzhydryl derivatives. Mechanistic studies reveal that the cyclopropane rearrangement involves a Lewis acid catalyzed ring-opening followed by the 1,2-migration of an aryl group. The possibility of controlling the absolute stereochemistry of the generated stereogenic allylic carbon center using a chiral sulfonium ylide is demonstrated.