Methylene derivatives acetolysis

Notable progress in the structural analysis of methylene derivatives of the polyhydric alcohols resulted from the investigations of Hann, Hudson and their co-workers26 80,40-4 into the behavior of these compounds during acetolysis. It was found that a mixture of acetic anhydride, acetic acid and 1-2% sulfuric acid ruptures preferentially any methylene bridge which spans a primary and a secondary position, giving the acetate ester of the primary hydroxyl and the acetoxymethyl ether of the secondary hydroxyl subsequent treatment with sodium methoxide removes each of these substituents. Under similar conditions, the acetolysis of a benzylidene compound results in the replacement of the arylidene residue, wherever it is located in the molecule, by two acetyl groups.16 29 47 48... 

Following the observation that benzyl ethers are cleaved by acetic anhydride in the presence of sulfuric acid or perchloric acid, Allerton and Fletcher S extended the work to carbohydrate systems. 2,5-Di-O-benzyl-l,3 4,6-di-0-methylene-D-mannitol (12) gave 1,3,4,6-tetra-0-acetyl-2, 5-di-O-benzyl-D-mannitol in the presence of 0.09% of sulfuric acid, but, with 2.4% of the acid, the hexaacetate was formed. With 1,6-di-O-benzyl-2,4 3,5-di-0-methylene-L-iditol (13), brief acetolysis gave the di-0-acetyl-di-O-methylene derivative longer treatment gave the hexaacetate. 

By acetolysis of a- or /3-methylene acetals of polyols with trifluoroacetic anhydride-carboxylic acid mixtures, derivatives may be prepared71 that are O-acylated at the primary hydroxyl group, and that have free hydroxyl groups at certain secondary positions. 

One acetal group of the trimethylene derivative was shown to span positions 2 and 4 by the demonstration that the compound afforded 2,4-methylene-D-talitol when subjected to acetolysis and then to treatment with sodium methoxide.46 The two labile groups may have been of the 1,3 5,6-, 1,5 3,6- or 1,6 3,5-type, of which the first was highly probable accordingly the triacetal was named l,3 2,4 5,6-trimethylene-D-talitol (XXXII).46... 

Trifluoroacetic anhydride-acetic acid, when used for the acetolysis of methylene acetals of alditols, shows the same specificity as acetic anhydride-sulfuric acid. - However, the products formed can be converted, by very mild hydrolysis, into the acetate-hydroxy derivative (6), because of facile cleavage of the (trifluoroacetoxy) methyl ether linkage (5). 

Acetolysis of the 6a,7a-methylene-4/3-mesyIoxycholestane (136) gave the 7a-acetoxymethyl compound (137) as the sole product.The ring expansion of steroidal halogenocyclopropyl acetates derived from enol acetates and haloge-nated carbenes has been studied in further detail.The base-catalysed reactions... 

The structures of many methylene sugar derivatives have not been determined, but those of many of the alditol derivatives are known. The greater ease of acetolysis of methylene groups attached to primary hydroxyls over those attached to secondary hydroxyls, has been of considerable value in the elucidation of the structures of these compounds by Hudson and co-workers (96), Thus the linkages at carbons 1 and 6 of 1,3 2,4 5,6-tri-O-methylene-D-glucitol are cleaved with sulfuric acid in acetic anhydride and acetic acid as shown in the formulas. The structure of the mono-0-methylene-D-glucitol is demonstrated by its oxidation with periodic acid... 

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