Dithioacetals acetylated

Triazoline imino sugar derivatives 297 that are prospective glycosidase inhibitors have been prepared as single diastereomers in high yield via an lAOC reaction of in situ generated azido alkene 296 (Eq. 32) [78]. m-CPBA oxidation of the dithioacetal groups in the 0-acetylated 5-azido-5-deoxydibenzyl dithio-acetal of o-xylose or D-ribose 294 to the bis-sulfone 295, followed by loss of HOAc between C-1 and C-2 provided the lAOC precursor 296. 

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... 

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-... 

Dialkyl dithioacetal derivatives of ketoses, such as D-fiuctose and L-sorbose, me inaccessible directly from the parent sugars, the ketose undergoing extensive decomposition under the conditions employed for mercaptaladon of aldoses. Such derivatives can, however, be prepared by indirect methods. Acetylation of D-fiuctose [40] and L-soibose with acetic adiydride and zinc chloride [41] leads to good yields of acyclic pentaacetates in which foe ketose carbonyl is not involved in a cyclic acetal. Subsequent treatment of these acetylated derivatives with thiols affords foe acetylated dialkyl dithioacetals in satisfactory yields, and conventional deacetylation affords foe unprotected dialkyl dithioacetals [40,41]... 

The peak of the molecular ion is, surprisingly, absent from the mass spectra of fully acetylated ethylene dithioacetals.41 Their fragmentation consists principally of elimination of CHaCOiH, CHaCOj-, CHsCO, and ketene in various combinations. The most intense peaks of the spectra are those at m/e 43 (CH.CO ), 45 (CHsS ), 01 (EtS ), and Xi (m/e 105) ... 

Fully acetylated diethyl dithioacetals are to be preferred to ethylene dithioacetals for analytical applications, as the mass spectra of the latter do not contain the peak of the molecular ion, and provide no information additional to that which can be drawn from the spectra of the former. 

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