Stereoselectivity of Diels–Alder Reactions of 6,7-Dioxabicyclo[3.2.2]nona-3,8-dien-2-one and 6,7-Diethoxycarbonyl-6,7-diazabicyclo[3.2.2]nona-3,8-dien-2-one
A Diels–Alder reaction of 6,7-dioxabicyclo[3.2.2]nona-3,8-dien-2-one (2) with cyclopentadiene gave the cis-endo-[4+2] adduct and the trans-endo-[4+2] adduct. Their yields were improved when the reaction was carried out under high-pressure conditions. The reaction of 6,7-diethoxycarbonyl-6,7-diazabicyclo[3.2.2]nona-3,8-dien-2-one (3) gave the cis-endo-[4+2] adduct. Reactions of 2 and 3 with isobenzofuran