Conformation of 1-oxy cyclohexenes deriving from Diels-Alder cycloaddition: Spectroscopic and X-ray crystal structure analysis

For cycloadduct (6), derived by reaction of the (Z)-oxy diene (7) with the dienophile (8), the newly formed cyclohexene ring is shown by spectroscopic and X-ray crystal structure analysis to be based on the half-chair conform ation (9). This contrasts with analogous diastereomeric adducts from (E)-ox y dienes, which are based on the ring-flipped conformation (4). The determi nant for this conformational difference is suggested to be the stereoelectr onic preference of the allylic oxy substituent, in (4) and (9), for a pseud oaxial orientation to the double bond of the cyclohexene system.