Cyclopenta[c]pyrans from 6-oxo-6H-1,3,4-oxadiazines†

Abstract

Prepared in a three-step sequence including acid-catalysed cycloaddition of cyclopentadiene to 6-oxo-6H-1,3,4-oxadiazines, dehydrogenation with DDQ of the dihydro-α-pyrones formed and reduction of the resulting α-pyrones with DIBAL-H, 1,4-disubstituted cyclopenta[c]pyrans are shown to undergo electrophilic substitution; the molecular structures of 1-(4-anisyl)-4-phenylcyclopenta[c]pyran and 4-isopropyl-1-phenylcyclopenta[c]pyran-7-carbaldehyde have been determined by single crystal X-ray diffraction studies.