INTRAMOLECULAR PICTET-SPENGLER REACTION OF N-ALKOXYTRYPTAMINES .3. STEREOSELECTIVE SYNTHESIS OF (-)-DEBROMOEUDISTOMIN-L AND (-)-O-METHYLDEBROMOEUDISTOMIN-E AND THEIR STEREOISOMERS

The N-hydroxytryptarnines 10 and 11 were converted into the N-alkoxy derivatives 3234 (overall yield 57-72%) by successive protection with [2-(trimethylsilyl)ethyl}chloroformate providing 27 and 28, reaction with functionalized chloromethyl sulfides, and deprotection with a “naked” fluoride. Intramolecular cyclization succeeded with 33 and 34 by reduction of the methyl ester with DIBAL and treatment with TFA to give diastereomeric pairs with a slight selectivity for the trans isomer (53-81%, cis/trans ~ 35/65). Removal of the BOC group gave de-bromoeudistomin L ((-)-le), its three stereomers (42a,b and (+)-le), O-methyldebromoeudistomin E ((-)-lf), and its stereomer 43. © 1990, American Chemical Society. All rights reserved.