SYNTHETIC APPROACHES TOWARD ECTEINASCIDINS .1. PREPARATION OF AN -2-ARYLIDENE-3-BENZYL-1,5-IMINO-3-BENZAZOCIN-4-ONE HAVING A PROTECTED PHENOL IN THE E-RING

A synthetic strategy for the preparation of ecteinascidins isolated fr om the Caribbean tunicate Ecteinascidia turbinata and an efficient syn thesis of a key tricyclic lactam intermediate 32 are described, The ke y step is the intramolecular cyclization of the allylic alcohol 15 to the (E)-1,5-imino-3-benzazocine 16, Cyclization of 15 (R = Me, Bn) aff orded the desired product 16 in good yield, However, treatment of 15 ( R = MOM) under acidic conditions gave compound 18 in high yield, the s tructure of which was determined by X-ray crystallography, Finally, 16 was converted into (E)-N-methyltricyclic lactam 32 that can serve as a synthetic precursor of ecteinascidins.