Ethylidene, Isopropylidene, Cyclohexylidene and Benzylidene Acetals

Trichloroethylidene acetals are readily dechlorinated by tributyltin hydride, thus providing convenient access to ethylidene acetals with endo-H configuration.  

A number of new acetonation conditions have been examined. Use of acetone in the presence of K 10 clay gave the 2,3-0-isopropylidene derivatives of d-ribofuranose and L-rhamnopyranose and the expected di-O-isopropylidene derivatives of D-xylose, D-glucose, D-galactose and D-mannose in excellent yields. Good to excellent yields of the expected acetonides of methyl a-D-manno-, a-D-gluco-, and a-D-galacto-pyranoside as well as of D-mannose have been obtained with acetone and titanium(IV) chloride supported on modified silica gel. H3PM012O40 was the most active of 18 heteropolyacids examined as catalysts in the acetonation of L-sorbose.  

Isopropylidenation of methyl a-D-glucoseptanoside with limited quantities of 2,2-dimethoxypropane and TsOH in DMF gave 5 as the major product. The two octonolactones obtained in near equal proportions by Kiliani ascent from 

Carbohydrate Chemistry, Volume 30 The Royal Society of Chemistry, 1998 

The cyclohexylidenation of o-mannose diethyl dithioacetal aimed at the preparation of the fully 0-protected aldehydo-D-meainose derivative 8 has been described.  

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