PREPARATION OF ALKYL-SUBSTITUTED INDOLES IN THE BENZENE PORTION .9. SYNTHESIS OF ARBONYL-8-FORMYL-1,1A,2,8B-TETRAHYDROAZIRINO[2',3' 3,4]PYRROLO[1,2-A]INDOLE - MODEL STUDY FOR THE ENANTIOSPECIFIC SYNTHESIS OF AZIRIDINOMITOSENES/

Effective pathways for an enantiospecific synthesis of b-tetrahydroazi rino[2',3':3,4]pyrrolo[1,2-alindole (8) were investigated as a prelimi nary experiment aiming at chiral syntheses of aziridinomitosenes 5 and rmyl-7-hydroxy-1,1a,2,8b-tetra-hydroazirino[2',3': 3,4]pyrrolo[1,2-a] indole (6a). An aldehyde 14, derived from L-serine was condensed with 2-lithio-1-(phenylsulfonyl)indole (10) to afford diastereomers 15a and 15b, whose stereochemistry was unambiguously determined by H-1-NMR st udies of the 1,3-dioxane derivatives 17a, 17b, and 18 as well as the X -ray crystallographic analysis of a dihydropyrrolo[1,2-a]indole deriva tive 31a. The latter compound was prepared from 15a via the following operations (Chart 5): (i) removal of the acetonide and the indole-prot ecting groups, followed by acetylation to form 29a, (ii) Vilsmeier rea ction to produce 30a, and (iii) hydrolysis of acetyl groups, partial m ethanesulfonylation (mesylation), and treatment with potassium carbona te in acetonitrile. A diastereomer 31b was obtained from 15b in a simi lar manner. Both isomers 31a and 31b afforded the desired compound 8 u pon treatment with a mesylation reagent followed by potassium tert-but oxide in tetrahydrofuran.