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?

RSC Advances Pub Date: 2014-11-21 DOI: 10.1039/C4RA13374A

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.

Graphical 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
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