D-Glycals

Studies with other glycosidases " " showed, however, that effective inhibition by glycals is not a general phenomenon, and that inhibition does not correlate well with hydration to 2-deoxy-o-hexoses. Based on kinetic considerations, the interaction of glycosidases with D-glycals (A) can be described by the following scheme ... 

Interaction of Glycosidases with D-Glycals and Related Compounds (See Text for Definition of Kinetic Constants)... 

In addition, iodine snccessfnlly catalyzed the electrophilic snbstitntion reaction of indoles with aldehydes and ketones to bis(indonyl)methanes [225], the deprotection of aromatic acetates [226], esterifications [227], transesterifications [227], the chemoselective thioacetalization of carbon functions [228], the addition of mercaptans to a,P-nnsatnrated carboxylic acids [229], the imino-Diels-Alder reaction [230], the synthesis of iV-Boc protected amines [231], the preparation of alkynyl sngars from D-glycals [232], the preparation of methyl bisnlfate [233], and the synthesis of P-acetamido ketones from aromatic aldehydes, enolizable ketones or ketoesters and acetonitrile [234],... 

J. S. Yadav, B. V. S. Reddy, K. Bhaskar Reddy, and M. Satyanarayana, CeCl3 7HzO A novel reagent for the synthesis of 2-deoxysugars from D-glycals, Tetrahedron Lett., 43 (2002) 7009-7012. 

In comparison to the previous example, the ester hydrolysis was significantly slower requiring a reaction time of 60 h to consume tri-O-acetyl-D-glucal 163 and afford the target compound 161 in 80% yield, with D-glycal 164 as a minor by-product (12.0%). 

Not only alkenes but also other unsaturated substrates were similarly converted into v/oazidophenylselenyl derivatives, e.g. 3,4-dihydro-2//-pyran (74%), methyl methacrylate (75%), etc. Tri-O-methyl-D-glycal and tri-O-acetyl-D-glycal also gave the expected products the former two stereoisomers in a 4 6 ratio for cis and trans, and the latter another two in the reverse ratio. 

The azidonitration route to 2-amino-2-deoxy sugars from D-glycal should be compared with the alternative route exploiting the addition of nitrosyl chloride (Section 7.2.1.1). Both methods have been tested on the synthesis of intermediates of D-lactosamine, and the azidonitration method was considered more efficient95. 

Roush WR, Sebesta DP, Bennett CE (1997) Stereoselective preparation of 2-deoxy-P-giycosides from giycai precursors. 1. Stereochemistry of the reactions of D-glycal derivatives with phenyisuifenyi chloride and phenyiseienyl chloride. Tetrahedron 53 8825-8836... 

Azidonitration of D-glycal triacetates was the first step in a synthesis of C-glycosyl derivatives of 2-amino-2-deoxy sugars which is covered in Chapter 9. yJ-o-Glucopyranoside tetranitrate and -cellobiose octanitrate are referred to In Chapter 21. 

A detailed study on the conventional benzoylation and pivaloylation of d-fructose has been undertaken following consideration of factors such as equilibration rates and the distribution of tautomeric forms at given temperatures, practical procedures for the selective preparation of either pyranose, furanose, or acyclic peresters have been worked out. The selectivities in electrochemically induced esterifications of D-glycals have been investigated and compared with selectivities in chemically induced ester formations. ... 

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