Tetrahydroisoquinolines. Part 3. Stereoselective synthesis of cis- and trans-1,4-disubstituted N-methyl-1,2,3,4-tetrahydroisoquinolines as their tricarbonylchromium complexes

Abstract

The 1-exo proton of tricarbonyl-4-exo-methyl- or tricarbonyl-4-exo-ethyl-2-methyl-1,2,3,4-tetrahydroisoquinolinechromium (6) and (7) can be regio- and stereo-selectively removed by t-butyl-lithium and replaced with a variety of electrophiles to give cis-1,4-disubstituted 2-methyl-1,2,3,4-tetrahydroisoquinoline complexes. Oxidative decomplexation generates the corresponding cis-1,4-disubstituted tetrahydroisoquinolines. Similar methodology applied to tricarbonyl (4-exo-trimethylsilyl-2-methyl-1,2,3,4-tetrahydroisoquinoline)chromium (15) gives, after desilylation, 1-exo-substituted tetrahydroisoquinoline complexes.