Dithioacetals ketoses

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]... 

Acylation66 of D-fructose leads67 to substantial yields of a completely esterified, acyclic derivative (6) in which the ketonic center exists as a free carbonyl group, and provides an indirect route for the synthesis of ketose dialkyl dithioacetals, as 6 reacts with two equivalents of thiol under acid catalysis to produce68 the acylated dithio-acetal 7, which can subsequently be saponified to yield the free... 

Treatment of 2-deoxy-3,4 5,6-di-O-isopropylidene-D-arahtno-hex-ose diethyl dithioacetal (128a) with butyllithium in tetrahydrofuran produced a carbanion that is stable by virtue of having no electronegative substituent at C-2 this anion subsequently reacted with iodo-methane to afford255" l,3-dideoxy-4,5 6,7-di-O-isopropylidene-D-arabino-heptulose diethyl dithioacetal (128b) in 82% yield (see Section 11,5). This reaction provides a useful route to 1,3-dideoxy-2-ketoses. 

Other developments in the chemistry of dithioacetals included preparation of the first dithioacetal of a ketose (D-fhictose), and the establishing of the technique of mercaptolysis for the fragmentation of polysaccharides. In other hands, the technique of mercaptolysis has been applied successfully for determination of structure, notahly with... 

The sugar dithioacetals are perhaps the best intermediates except that the reaction conditions may be too severe for some sugars, such as the disaccharides, which may be hydrolyzed (21). The ketoses are too acid-sensitive for direct mercaptalation D-fructose diethyl dithioacetal has been prepared by Wolfrom and Thompson only by an indirect method (i). The reduction of the acid chloride has not been extensively used but should be limited only by the availability of the acetylated acids (p. 309) 22). 

Through variation of the conditions employed for the hydrolysis, in the presence of mercuric compounds, of the thioalkyl groups from aldose or ketose dithioacetals (mercaptals), pyranosides, furanosides, 1-thioglyco-sides, or acetals may be obtained 6, 38-40). Several natural 1-thioglyco-... 

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