DIELS-ALDER REACTION OF BENZYLIDENE(CYANO)METHYL-1,3-BENZOXA THIAZOLES AS STABLE 1-AZABUTA-1,3-DIENES

Diels-Alder reactions of benzylidene(cyano)methyl-1,3-benzothiazoles 2 and -1,3-benzoxazoles 3 as 1-azabuta-1,3-dienes are described. The di enes 2, 3, featuring stabilized imine moieties in the form of heteroar omatic rings, react with both electron-deficient and electron-rich die nophiles 7-9 to give corresponding cycloadducts 10-15 regioselectively . Cycloadditions of the intramolecular systems 18c, d and 19c, d proce ed smoothly via an exo-transition state, stereoselectively affording p olycyclic compounds 20c, d and 21c, d in good to excellent yields. X-R ay crystallographic studies of compounds 12e, 13a and 14b are also rep orted.