Methylenepyran unsaturated Fischer carbene complexes from γ-methylpyrylium salts and alkynylcarbenes. Evolution to spiro-pyran-cyclopentenone compounds
Résumé
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 Michaël-type acceptors. The new carbenes 3 evolve in CH2Cl2 solution at room temperature to provide spiro-fused-pyran-cyclopentenenone 4 and polysubstituted cyclopentenones 5.