Inter- and intramolecular Diels–Alder reaction of benzoxazole-based azadienes

Abstract

Inter- and intramolecular Diels–Alder reactions of novel azadienes 2 and 3 are described. The dienes 2 and 3 react with electron-rich dienophiles, vinyl ethers 7a,b and p-methoxystyrene derivatives 7c,d to afford the corresponding cycloadducts 8 and 9, regioselectively. The azadienes 2 and 3 also undergo tandem transesterification and intramolecular cycloaddition with cinnamyl alcohols 13 in the presence of stannoxane catalyst 14 to give tetracyclic compounds 15 and 16 in one step. In a tandem process, the geometries of the dienophile components of 13 were transmitted into the cycloadducts 15 and 16.