作者:Igor A. Mikhailopulo、Grigorii G. Sivets
DOI:10.1002/(sici)1522-2675(19991110)82:11<2052::aid-hlca2052>3.0.co;2-7
日期:1999.11.10
The reaction of (diethylamino)sulfur trifluoride (DAST) with methyl 5-O-benzoyl-beta-D-xylofuranoside (1) followed by column chromatography afforded the riboside 2 (62%) and the ribo-epoxide 3 (18%) (Scheme 1). Under similar reaction conditions, the alpha-D-anomer 4 gave the riboside 5 and the difluoride 6 in 60 and 9% yield, respectively Treatment of the beta-D-xyloside 10 with DAST gave, after chromatographic purification, the riboside 11 as the principal product (48% 1 Scheme 2). These results suggest that the C(3)-O-SF2NEt2 derivatives were initially formed in the case of the xylosides studied. The distinctive feature of the reaction of DAST with the beta-D-arabinoside 12 consists in the formation of a 3- or 5-benzylideneoxoniumyl-substituted intermediate on one of the consecutive transformations, which finally give rise to the inversion of the configuration at C(3) affording the xylosides 17 (18%) and 18 (55% ): the lyxoside 14 was also isolated from the reaction mixture in a yield of 25% (Scheme 3). In the presence of the non-participating 5-O-trityl group, i.e.,from the reaction products of 21 with DAST. the compounds 23 and 23 were isolated in 16 and 52% yield, respectively (Scheme 4). It may be thus reasonable to conclude that, in the case of the beta-D-arabinosides 12 and 21, the principal route of the reaction is the formation of the intermediate C(2)-O-SF2NEt2 derivative. Unlike the alpha-D-arabinoside 26 was converted to the lyxo-epoxide 25 (53%) and the lyxoside 27 (14%), which implies the intermediate formation of the C(3)-O-SF2NEt2 derivative (Scheme 5).