Various kinds of nonbranched and methyl-branched 6-deoxyh,ex-5-enopyranoside derivatives were prepared from 6-bromo-6-deoxy or 6-O-p-tolylsulfonylhexopyranoside in a ·one-pot procedure by a successive treatment with iodide anion and 1,8-diazabicyclo[5.4.0]undec-7-ene in dimethyl sulfoxide. The scope and limitations of this reaction have become apparent by observing the reactions of 18 substrates. The yields of altropyranoside and 2-deoxyribo-hexopyranoside derivatives were high, except for the 2,3-anhydropyranoside derivative. Methylbranched 6-deoxyhex-5-enopyranoside derivatives were also obtained in practical yields.6-Deoxyhex-5-enopyranosides are very useful precursors in biologically important natural-product synthesis, such as 6-deoxy-L-hexose!) and the cyclitol derivative?} In general, 6-deoxyhex-5-enopyranosides have been synthesized by treating the corresponding 6-bromo derivative with AgF/pyridine,3} 1,or NaH/N,Ndimethylformamide (DMF).5) These methods, however, have some limitations, such as displacement reactions with fluorine, acyl migration reaction, and deacylation. At the beginning of our 5-enopyranosides syntheses, we used DBU/CH 3 CN as a useful synthetic method; however, it required a longer reaction time and gave side products in many cases. Furthermore, this method did not work well in the case of methyl-branched series. Regarding another type of elimination reaction, S. Hannesian has reported on the use of DBU/DMSO in the synthesis of carbohydrate derivatives containing the vinylic thioether group by eliminating the mesyl group. In that report, the elimination with DBU/DMSO under heating for 2.5 h at 85°C gave the corresponding 2,3-unsaturated derivative in good yield.6 ) The strong base ability of DBU/DMSO probably suggests the intermediacy of the DMSO carbo anion in DMSO. If we can use DBU/DMSO methods in the syntheses of hex-5-enopyranosides, the elimination reaction may progress faster than DBU/CH 3 CN. In order to contribute to the development of such 6-deoxyhex-5-enopyranosides syntheses, the authors examined DBU/DMSO methods and communicated a convenient and general method for synthesizing 6-deoxyhex-5-enopyranosides from the corresponding 6-bromo-6-deoxy-or 6-O-p-tolylsulfonylhexopyranosides in a one-pot procedure by a successive treatment with the iodide anion, DBU, and molecular sieves (MS) 4A in dimethyl sulfoxide (DMSO), instead of CH 3 CN. This paper describes details concerning the communication 7 } as well as the scope and limitations of the above method by using 18 substrates, i.e., nonbranched (1, 5, 8, 12, 14, 16, 18, 20, 22, 25, and 28) and a methyl-branched series (32, 34, 36, 38, 40, 42, and 44) (Chart 1, Figs.
