Chemical and enzyme-catalysed syntheses of enantiopure epoxide and diol derivatives of chromene, 2,2-dimethylchromene, and 7-methoxy-2,2-dimethylchromene (precocene-1)

Procaryotic (bacterial) dioxygenase-catalysed asymmetric dihydroxylation of chromene and 2,2-dimethylchromene to yield the (4S)-enantiomers of the corresponding cis-diols exclusively is reported. The epoxide, and derived cis- and trans-diol products from the previously reported eucaryotic (mammalian) metabolism of precocene-1 (7-methoxy-2,2-dimethylchromene), and the corresponding epoxide and diol derivatives of chromene and 2,2-dimethylchromene, have now been obtained in enantiopure form by chemical resolution of the corresponding bromohydrins using methoxy(trifluoromethyl)phenylacetic acid (MTPA) or camphanate esters, The absolute configurations of the epoxides, cis- and trans-diols have been determined by chemical synthesis from, and stereochemical correlation with, the corresponding camphanate and MTPA esters, X-Ray crystal structure analysis has provided an unequivocal method for assignment of the absolute stereochemistry in each case.