Very rapid formyl shifts in 1-formylindenes; strict stereospecificity and exclusive 1,5-sigmatropy
Abstract
Rapid formyl migration establishing an equilibrium between (1) and (4) is revealed by trapping, transfer of non-equilibrium spin, and racemisation experiments; racemisation of (11) is twice as fast as its conversion into (3), and interconversion of (2) and (9) is stereospecific in accord with the exclusive occurrence of 1,5,-sigmatropy.