Synthesis of protoberberines using a silyl-directed Pictet–Spengler cyclization
作者:Paul S Cutter、R.Bryan Miller、Neil E Schore
DOI:10.1016/s0040-4020(02)00010-8
日期:2002.2
Five naturally-occurring protoberberines have been synthesized in enantioenriched form by alkylation by two different 2-trimethylsilylbenzyl chlorides of four tetrahydroisoquinolines, derivatized with Meyers' formamidine valinol methyl ether chiral auxiliary. Silyl-directed Pictet-Spengler cyclization of the ensuing 3,4-dimethoxy-2-trimethylsilylbenzyl tetrahydroisoquinolines leads to four of the target protoberberines in excellent yield and complete regioselectivity. In the fifth case, the 3,4-methylenedioxy analog gives a mixture of protoberberine and a product of ring closure at C6 of the benzyl moiety in a 3:4 ratio. (C) 2002 Published by Elsevier Science Ltd.
Total Synthesis of (−)-Tetrahydropalmatine via Chiral Formamidine Carbanions: Unexpected Behavior with Certain Ortho-Substituted Electrophiles
作者:Mark A. Matulenko、A. I. Meyers
DOI:10.1021/jo951611q
日期:1996.1.1
established using an ortho-substituted hydroxymethylbenzene electrophile protected as a silyl ether to ultimately provide (-)-tetrahydropalmatine in 88% ee. Additionally, we have discovered limitations with ortho-substituted electrophiles in the asymmetric formamidine alkylation. These electrophiles have the potential to disrupt the lithium formamidine chelate and cause the selectivity in the alkylation to