A general method for the resolution of cyclic trans-bromohydrin enantiomers. Absolute configuration by crystal structure analysis of a 2-methoxy-2-phenyl-2-trifluoromethylacetate (MTPA) diastereoisomer

Abstract

trans-Bromohydrins of 1,2,3,4-tetrahydronaphthalene (1a), 1,2,3,4-tetrahydroanthracene (1b), and 1,2,3,4-tetrahydrophenanthrene (1c) and (1d) were isolated in optically pure forms by reductive cleavage of the corresponding 2-methoxy-2-phenyl-2-trifluoromethylacetate (MTPA) diastereoisomers (2a–d) which had been separated by preparative h.p.l.c. Using reactions with established mechanisms and stereochemistry, the configurations at the chiral centres in the bromohydrins (1) were correlated with those in the tetrahydroepoxides (5), the arene oxides (7), and cis-(3) and trans-(4) tetrahydrodiols. An X-ray structure analysis of the 1,2,3,4-tetrahydroanthracene bromo-MTPA ester (+)-(2b_E) indicated the trans equatorial quasi-equatorial conformation and confirmed the absolute stereochemistry of the MTPA group [derived from (–)-acid] as (S).