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Paper | Special issue | Vol 74, No. 1, 2007, pp.701-720
Published online, 30th October, 2007
DOI: 10.3987/COM-07-S(W)56
Synthesis of Both Enantiomers of Protoberberines via Laterally Lithiated (S)-4-Isopropyl-2-(o-tolyl)oxazolines

Tsutomu Fukuda and Masatomo Iwao*

*Department of Applied Chemistry, Faculty of Engineering, 1-14, Bunkyo-machi, Nagasaki 852-8521, Japan

Abstract

The addition of the laterally lithiated (S)-4-isopropyl-2-(o- tolyl)oxazoline (1) to 6,7-dimethoxy-3,4-dihydroisoquinoline (2) proceeded in modest diastereoselectivity. However, the addition products (3a) and (3b) were easily separated by column chromatography over silica gel. Acid-catalyzed lactamization of 3a and 3b followed by LiAlH4-reduction afforded the corresponding optically pure protoberberines (8a) and (8b), respectively. This procedure was successfully applied to the synthesis of both enantiomers of xylopinine and bharatamine.