Synthesis of Chiral Epibromohydrin Monomers and Effects of Solvent and Initiator Concentration on their Oligomerization

概要

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D-mannitol is a common chiral starting material and utility of chiral glycerin derivative as a versatile substrate for the enantioselective syntheses of natural products is known. Optically active 1,2-0-isopropylidene-(S)-glycerol (4) was obtained as an intermediates from D-mannitol (1). (S)-Epibromohydrin (8) was derived from (R)-3-tosyloxy-1,2-propanediol (6). On the other hand, (R)-Epibromohydrin (11) was formed from (R)-glycidol (7) and (R)-3-mesyloxy-1,2-epoxypropane (9). Oligomerization of both epibromohydrin was perfomed in the presence of Boron trifluoride ether complex (BF_3OEt_2 : initiator), and molecular weights of the products were determined by GPC analysis. Nonpolar solvent such as benzene and 1,2-dichloroethane gave the oligomers in high conversions, and tetramer, octamer or higher were major components in the products. Also, 1,2-dimethoxyethane gave poor conversion. The highest yield was attained at about 1 to 20 molar ratio of the initiator to the monomers.