Methylenepyran unsaturated Fischer carbene complexes from γ-methylpyrylium salts and alkynylcarbenes. Evolution to spiro-pyran-cyclopentenone compounds

Abstract Push–pull methylenepyran compounds 3 containing ferrocenyl or aryl groups are synthesized from reaction of condensation between γ-methyl-pyrylium salts 1 as precursors of γ-methylenepyrans and alkynylcarbene complexes 2 as Michael-type acceptors. The new carbenes 3 evolve in CH 2 Cl 2 solution at room temperature to provide spiro-fused-pyran-cyclopentenenone 4 and polysubstituted cyclopentenones 5 .