Synthesis of erythrina and related alkaloids. 17. Total synthesis of dl-coccuvinine and dl-coccolinine

Total synthesis of dl-coccuvinine la and dl-coccolinine 2a, abnormal-type erythrinan alkaloids lacking the C(16) O-function at the aromatic ring, was effectively achieved by using the Diels-Alder reaction of dioxopyrroline. Isoquinolino- pyrrolinedione 6a, a key dienophile, was synthesized via the tetrahydroisoquinoline 5a, which was prepared by Bischler- Napieralski cyclization of the amide 4a at the unactivated position. The Diels-Alder adduct 7a of 1,3-bis(trimethylsilyloxy)- butadiene with 6a with converted stereoselectively into these alkaloids in short steps.