Amide acetals reactions, review

Pinner synthesis of orthoesters starting from alkoxymethyleneiminium salts (410 equation 192) (imino ester hydrohalides) is a standard procedure, which has been reviewed several times.For some more recent results see ref. 7. Closely related to this reaction is the alcoholysis of IV-alkyl- and NJ -di-alkyl-alkoxymethyleneiminium salts or acid amide-acid halide adducts. Orthoesters are formed via N//-dialkylalkoxymethyleneiminium salts when amide acetals (411 Scheme 74) are alcoholyzed in the presence of acetic acid. - ... 

Synthesis of Monosaccharide Derivatives.—New approaches to the synthesis of glycosides, including the alkoxylation of N-furanosyl-lactams, the reaction of l-0-acetyl-2,3,5-tri-0-benzoyl-P-D-ribofuranose with cyclic amide acetals derived from vicinal diols (see Vol. 10, p. 16), the Lewis acid-catalysed alcoholysis of sugars with an activated anomeric centre (see Vol. 10, p. 11), and the glycosidation of glycopyranosyl halides catalysed by silver trifluoromethanesulphonate (triflate), have been reviewed. A general review of carbonyl compounds has also dealt with some aspects of glycoside synthesis. 

As mentioned above, the bis-amides 9a are used as precursors in the synthesis of Af-acylenamines. The conditions used for this reaction depend on the purpose of the synthesis and are described in numerous works, and reviewed in a series of articles35-37. The acid catalyst is usually concentrated sulfuric acid, but a successful application of 85% phosphoric, chlorosulfonic, methanesulfonic and formic acids was reported, and reactions were also conducted in the presence of anhydrous hydrogen chloride35. The solvents used are usually glacial acetic acid and chlorinated hydrocarbons. It is believed that the water necessary for the formation of the bis-amides under anhydrous conditions is obtained from conversion of the carboxylic acid to the anhydride, or even the sulfuric acid35. 

Numerous examples of such reactions (equation 34) have been reported in earlier reviews ". In the well-known standard synthesis of alkoxyalkynes f reaction of acetals of chloroacetaldehyde 52 with sodium amide in liquid ammonia has been used to generate sodium alkoxyacetylide 54. Recently, this elimination procedure has been further improved by using lithium diethylamide in THE solution (equation 35)". In this work" in situ generated lithium alkoxyacetylide 56 was subsequently converted to either ethoxyacetylene 57 by quenching with saturated aqueous sodium diioride, or ethoxyethynyl carbinols 58 by subsequent reaction with ketones or aldehydes. 

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