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Acid promoted cyclisation of homochiral (R)-N-(3,4-dimethoxyphenethyl)-halostachine proceeds with almost total racemisation to yield 1-phenyl-N-methyl-1,2,4,5-tetrahydrobenz[d]azepine (e.e. 6%). Coordination of the cyclisation precursor to the tricarbonylchromium(0) moiety renders the cyclisation completely stereospecific to afford, after decomplexation, homochiral (+)-(R)-1 -phenyl-N-methyl-1,2,4,5-tetrahydrobenz[d]azepine. (-)-(1R,2S)-N-(3,4-Dimethoxyphenethyl)ephedrine undergoes acid mediated cyclisation to furnish trans-(-)-(1R,2S)-1-phenyl-2-methyl-N-methyl-7,8-dimethoxy tetrahydrobenzazepine as a single diastereoisomer. In contrast, the epimeric cyclisation precursor (-)-(1R,2R)-N-(3,4-dimethoxyphenethyl)pseudoephedrine cyclises to give a mixture (ratio 91:9) of trans- and cis-1-phenyl-2-methyl-N-methyl-7,8-dimethoxy tetrahydrobenzazepine. However, cyclisation of the tricarbonylchromium(0) complex of(-)-(1R,2R)-N-(3,4-dimethoxyphenethyl)pseudo-ephedrine is completely stercoselective to yield trans-(+)-(1S,2R)-1-phenyl-2-methyl-N-methyl-7,8-dimethoxy tetrahydrobenzazepine after decomplexation. © 1991.

Original publication

DOI

10.1016/S0957-4166(00)82268-5

Type

Journal article

Journal

Tetrahedron: Asymmetry

Publication Date

01/01/1990

Volume

1

Pages

33 - 56