C-nucleoside studies. Part III. Glycofuranosylethynes from 2,3: 5,6-di-O-isopropylidene-D-mannose

Ethynylmagnesium bromide reacted with 2,3:5,6-di-O-isopropylidene-D- mannofuranose (2) to give 1,2-dideoxy-4,5:7,8-di-O-isopropylidene-D-glycero-D- talo-oct-1-ynitol (5) (65%), together with the o-glycero-D-galacto-isomer (3) (5%). The structure of the ethyne (5) was shown by conversion into the ethene (8) which, by ozonolysis, reduction and acidic hydrolysis in sequence, afforded crystalline D-glycero-D-talo-heptitol (D-volemitol). Oxidation of the ethyne (5) with manganese dioxide afforded crystalline 1,2-dideoxy-4,5:7,8-di-O- isopropylidene-D-manno-oct-1-yn-3-ulofuranose (14b), reduction of which with sodium borohydride gave mainly the diol (3). Treatment of the ethyne (5) with toluene-p-sulphonyl chloride in pyridine yielded 2,3:5,6-di-O-isopropylidene- ß-D-mannofuranosylethyne (16). Treatment of the ethyne (5) with benzoyl chloride followed by methanesulphonyl chloride yielded the 3-O-benzoyl-6-O- methylsulphonyl compound (21) which, on treatment with sodium methoxide, yielded 2,3:5,6-di-O-isopropylidene-a-D-talofuranosylethyne (22). Reaction of 1,2-dideoxy-4,5:7,8-di-O-isopropylidene-D-glycero-D-galacto-oct-1-ynitol (3) with toluene-p-sulphonyl chloride in pyridine yielded 2,3:5,6-di-O- isopropylidene a-D-mannofuranosylethyne (23). The mannofuranosylethynes (16) and (23) were degraded, by standard procedures, to the lyxofuranosylethynes (18) and (25), respectively. The glycofuranosylethynes (16) and (23), and (18) and (25) do not obey Hudson's rule. The c.d. of several compounds has been studied. Treatment of the mannofuranose (2) with ethylmagnesium bromide yields, by contrast, predominantly 7,8-dideoxy-1,2:4,5-di-O-isopropylidene-L-glycero-D- manno-octitol (30).