Glycals homologation

By application of various methods a series of ulosonic acids were readily accessed by homologation of glycal-type substrates [118]. One of the routes is illustrated by the preparation of 1-carbomethoxy glycals, suitable for functionalization to the isomeric heptulosonic acids (Scheme 38). Thus reaction of per-O-acetyl pyranosyl bromides 178 with Hg(CN)2 gave the cyanoglycosides 179, which in two steps were converted to the esters 181 [119,120],... 

The studies on homologation of glycals towards synthesis of the ulosonic acids have been extended recently by the use of an unique sequence of glycosylation. Thus, alkylidene[l,5]-C-H insertion forming the spiroketal glycosides led to DAH ammonium salt in few steps shown in Scheme 41 [121]. 

The preparation of glycopeptides by glycosylation of peptides with glycals using N-iodosuccinimide is covered in Chapter 3, and the preparation of chlorodeoxy-l,4 3,6-dianhydroalditols is mentioned in Chapter 18. The synthesis of 1-chloro-1-deoxy-ketoses by a 1 carbon homologation of lactone derivatives is outlined in Chapter 12. 

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