Diethyl dithioacetal

Diethyl dithioacetal derivatives of carbohydrates are generally crystalline compounds which are easily prepared from sugars in the combined or free form. In contrast to the mass spectra of the carbohydrate derivatives discussed above, the mass spectra of diethyl dithioacetals allow direct determination of molecular weight from molecular-ion peaks of... 

Actually, this decreased probability of fragmentation to primary radicals is pronounced in the mass spectra of diethyl dithioacetal derivatives of deoxy sugars and is particularly useful there also for locating the position of deoxy functions (13). 

Enzymic syntheses are considered next. Xylitol is a substrate for sheep-liver L-iditol dehydrogenase, a NAD-linked enzyme. 1-Deoxy-D-xylitol, prepared by Raney nickel reduction of D-xylose diethyl dithioacetal in a 27% overall yield from D-xylose, was also reported31 to be a substrate, although with a higher Km and lower Vmax. The product was assumed to be l-deoxy-D-f/ireo-pentulose because of the appearance of a yellowish fluorescent spot when a chromatogram was sprayed with acidic 3,5-aminobenzoic acid, resembling that formed from 1 -deoxyfructose. There was no more-rigorous characterization. 

Ethylene dithioacetals and diethyl dithioacetals have been investigated for a number of monosaccharides. The c.d. spectra show one, or two, c.d. band(s) of low intensity between 235 and 250 nm, and a third band of low intensity that peaks below 220 nm. These workers found no overall relationship between the configurational pattern of the monosaccharide and the sign of these bands. However, there does appear to be a correlation between the configurations of C-2, C-3 and C-4 and the sign of the c.d. band that peaks below 220 nm. 

C16H3oOsS2 2,3 4,5-Di-0-isopropylidene-D-gulose diethyl dithioacetal (IPGETA)97... 

C9H20O4S2 D-Ribose diethyl dithioacetal (DRETAC)316 CuH15C107 Tri-0-acetyl-/ -D-xylopyranosyl chloride (TACXYP)317 CuH1605 2,3,4-Tri-O-acetyl-a-D-xylopyranose (TAXYLP)318 C12H220,i -HoO 6-O-a-D-Galactopyranosyl-a.fl-D-glucopyranose, monohydrate (MELIBM03)319... 

CijHsbO Sj 2-S-Ethyl-2-thio-D-mannose diethyl dithioacetal EMANTA10 32 31 367 353... 

Scheme 18.—Proposed Mechanism for Photochemical Reaction of D-Galactose Diethyl Dithioacetal (44).

Extended irradiation of the diethyl dithioacetal 44 increases the yield of L-fucitol (46) at the expense of 1-S-ethyl-l-thio-D-galactitol (45) also galactitol (52) was isolated from the photolysis mixture.109 The intermediacy of 45 in the formation of 46, a possibility that was suggested by the extended photolysis of 44, is supported by the observation that irradiation of 45 in methanol produces L-fucitol (46) in 44% yield.109 (Compounds 47 and 52 also are formed during irradiation of 45, but in low yield.) The mechanism for sulfide photoreaction parallels that109 for the alkyl dithioacetals (see Scheme 18). 

C,5H4206S4 4,5,6-Tri-0-benzoyl-2,3-di-S-ethyl-2,3-dithio-D-allose diethyl dithioacetal (TBETHA)127... 

Scheme 22.—Photochemical Decomposition of o-Galactose Diethyl Dithioacetal.

The formation of 2,3,4-tri-0-acetyl-5-5-ethyl-5-thio-L-arabinose diethyl dithioacetal (67) when a-L-arabinopyranose tetraacetate (57) was treated o) th ethanethiol in the presence of either zinc chloride or boron trichloride was rationalised by the sequence of reactions shown subsequent work (see below) suggests that an orthoester may be inter-... 

Micheel then slightly modified his synthesis, starting from D-galactose diethyl dithioacetal (19) (Scheme 2).33 Selective tritylation of the 6-hydroxyl group followed... 

Dithioacetal derivatives have also been employed56 in reactions with 23. The primary hydroxyl group in 2,3 4,5-di-0-isopropylidene-D-galactose diethyl and dibenzyl dithioacetals is readily replaced by iodine, to give the expected 6-deoxy-6-iodo derivatives in almost quantitative yields. The secondary hydroxyl group in 5-0-benzoyl-2,3-0-isopropylidene-L-arabinose diethyl dithioacetal (32) was similarly replaced by iodine to give 5-0-benzoyl-4-deoxy-4-iodo-2,3-O-isopropylidene-D-xylose diethyl dithioacetal (33) however, a rearranged product, namely, 4-0-benzoyl-5-deoxy-5-iodo-2,3-0-iso-propylidene-L-arabinose diethyl dithioacetal (34) was also produced. 

In attempting to obtain 2,5-anhydro-D-glucose diethyl dithioacetal, Defaye58 performed the nitrous acid deamination of 2-amino-2-deoxy-D-glucose diethyl dithioacetal (27) under weakly acidic conditions (acetic acid and sodium nitrite), and obtained a principal product later shown59 to be ethyl 2-S-ethyl-l,2-dithio-a-D-mannofuranoside (28). Shortly before, Horton and coworkers60 had reported the forma-... 

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