ChemInform Abstract: Unusual Tandem Sequence of Oxa Diels—Alder Reaction, Retro Diels—Alder Reaction, and Oxa 6π‐Electrocyclic Ring Opening in the Reaction of 6‐Amino‐4‐(4‐methoxyphenyl)‐2H‐pyran‐2‐ones with Benzaldehydes.

Abstract

The oxa Diels–Alder reaction of 6-amino-4-(4-methoxyphenyl)-2H-pyran-2-ones with benzaldehydes took an unusual path whereby a tandem sequence of the oxa Diels–Alder reaction, retro Diels–Alder reaction, and 6π-electrocyclic ring opening of the pyran yielded 3-(4-methoxyphenyl)-5-phenyl-1-(piperidin-1-yl/pyrrolidin-1-yl)penta-2,4-dien-1-ones. The reaction took place in boiling toluene with a series of substituted benzaldehydes. An electron-donating group on benzaldehyde retarded the reaction, while an electron-withdrawing group favoured it, thus indicating the normal electron demand pathway.