Intramolecular Pictet-Spengler Reaction of N-Alkoxytryptamines. 3. Stereoselective Synthesis of (-)-Debromoeudistomin L and (-)-O-Methyldebromoeudistomin E and Their Stereoisomers

Article abstract of DOI:10.1021/jo00300a011

The N-hydroxytrypamines 10 and 11 were converted into the N-alkoxy derivatives 32-34 (overall yield 57-72percent) 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 (53-81percent, cis/trans ca. 35/65).Removal of the BOC group gave debromoeudistomin L ((-)-1e), its three stereoisomers (42a,b and (+)-1e), O-methyldebromoeudistomin E ((-)-1f), and its stereomer 43.