Asymmetric transformation. II. Racemization reaction of 1,4-benzodiazepinooxazole derivative.

Abstract

Optically active crystals of 10-bromo-11b-(2-fluorophenyl)-2, 3, 7, 11b-tetrahydrooxazolo-[3, 2-d][1, 4] benzodiazepin-6 (5H)-one were obtained by preferential crystallization; they were sometimes levorotatory and sometimes dextrorotatory. This phenomenon was proved to be an example of second-order asymmetric transformation between enantiomers. The rapid racemization reaction, which was essential for asymmetric transformation, was observed in methanol. The decrease of optical rotation obeyed good pseudo first-order kinetics and the half-lives of the racemization in methanol were estimated to be about 21 s at 30°C, 37s at 20°C and 70s at 10°C. The mechanism and factors which affect the rate of the racemization are discussed.