Reactivity of carbanions of Fischer-type carbene complexes with pyrylium salts. Synthesis and characterization of new gamma-methylenepyran carbene complexes via an addition-oxidation-deprotonation process

Abstract : The condensation reaction between gamma-unsubstituted pyrylium salts and carbanions of Fischer-type carbene complexes allowed the synthesis of new gamma-methylenepyran carbene complexes. NMR data, single crystal X-ray analysis, and DFT calculations suggest that these complexes have a partial pyrylium character due to the pi electron-accepting ability of the carbenic fragment and to the electron-releasing properties of the methylenepyran part. (C) 2002 Elsevier Science Ltd. All rights reserved.