Lewis and Brønsted Acid Cocatalyzed Reductive Deoxyallenylation of Propargylic Alcohols with 2-Nitrobenzenesulfonylhydrazide.

Reductive deoxyallenylation of sterically hindered tertiary propargylic alcohols was realized on reaction with 2-nitrobenzenesulfonylhydrazide (NBSH) by the combined use of Lewis and Brønsted acid catalysts. This method features a broad substrate scope, mild reaction conditions, and good functional-group tolerance, and affords various mono-, di-, and trisubstituted allenes in good-to-excellent yields. The synthetic utility of this method was demonstrated by the synthesis of 2 H-chromenes and 1,2-dihydroquinolines. [ABSTRACT FROM AUTHOR]