Spectroscopic, Optical, and Crystallographic Properties of (S)-(+)-cis-6'-Bromo-N-formylnorreticuline

Article abstract of DOI:10.1021/jo00142a025

A rotamer mixture of (S)-N-formyl-N-norreticuline (1) was brominated regioselectively in the 6'-position to afford the corresponding mixture of 6'-bromo rotamers (2) from which the thermodynamically less stable cis rotamer could easily be isolated by direct crystallization.This rotamer was stable in crystalline condition but equilibrated to a 1:2 cis-trans mixture on standing in solution.This equilibration was easily followed by observation of changes in optical rotation and the ratio of N-formyl protons in the NMR spectrum.Assigment of the cis structure to the rotamer isolated by crystallization was confirmed by a single crystal X-rayanalysis, which also confirmed the absolute configuration of this rotamer made independently from established stereochemical relationships.The crystals of 2 have space group P2₁ and cell dimensions a = 6.616 (1) Angstroem, b = 10.985 (1) Angstroem, c = 13.084 (2) Angstroem and β = 95.61 (1) deg.The structure was refined to an R factor of 4.3percent.