Formamidines in synthesis. An efficient one-pot synthesis of 7-substituted indolines via intramolecular cyclization of (2-phenethyl)formamidines. An asymmetric route to benzopyrrocoline alkaloids
摘要:
o-Chloro-beta-phenethylamines, transformed into the N-tert-butylformamidines, were found to be excellent precursors to indolines following benzyne formation. A series of methoxy-substituted o-chlorophenethylamines containing an N-alkyl or aryl substitutent were subjected to sec-butyllithium producing the ortho-lithiated aromatic which subsequently lost lithium chloride at temperatures ranging from -78 to -50-degrees-C. The resulting benzyne was intramolecularly trapped providing the titled heterocycles. Quenching the reaction resulted in elimination of the tert-butyl isocyanide (isolated after aqueous workup as tert-butylformamide) and protonation (or alkylation) of the 7-lithio position. Overall the yields for this process were 60-95% for a variety of N-substituted phenethylamines. In addition, a one-pot total asymmetric route to benzopyrrocoline alkaloids was featured using this benzyne trapping of chiral formamidines.
Recent progress using chiral formamidines in asymmetric syntheses
作者:A.I. Meyers
DOI:10.1016/s0040-4020(01)88523-9
日期:1992.3
The ability to generate a carbanion next to nitrogen in a chiral environment has led to a number of useful asymmetric routes to alkaloids and related substances. Mechanistic studies have been conducted to understand the nature of these alkylations.
Total synthesis of the dibenzopyrrocoline alkaloid S-(+)-cryptaustoline. Revision of absolute configuration due to an unusual inversion in stereochemistry
作者:A. I. Meyers、Thais M. Sielecki
DOI:10.1021/ja00007a084
日期:1991.3
The natural alkaloid cryptaustoline is (13R,7S)-(−)-1 due to the heretofore unprecedented inversion while the formamidine route led to the expected (13S,7R)-(+)-1