Dibromomethyl methyl ether, reaction

The most attractive approach for the 2-deoxy-p-glycosides starts with 2-bromo-2,6-dideoxyhexopyranosyl bromides (2 ) such as These are available regio- and stereo-specifically from readily accessible and simple precursors by reaction with dibromomethyl methyl ether (DBE) (22, 2 ). In principle, the formation of related compounds may be anticipated by the addition of bromine to glycal precursors. Previous studies (24-27). however, proved these processes to yield several isomers which renders this approach of little preparative value. 

Another procedure known as the dibromomethyl-methyl ether method (DBE-method) [20] leads to 2-deoxy-2-bromo- P- and in some cases to 2-deoxy-2-bromo-a glycosides. As with the HIS reaction, this represents an indirect synthesis of 2-deoxy sugars, because the C-2 halide substituent may be cleaved in a subsequent step. 

Sometimes the addition of a small amount of ZnCh as a catalyst is recommended, e.g. succinic acid is transformed to the dichloride only in the presence of this catalyst. It has to be noticed, however, that under these conditions hydrogen chloride is evolved and, therefore, acid sensitive compounds cannot be taken. Af-acylamino acid chlorides and chlorides of fully acetylated sugar acids are also obtainable in yields of 70% or more. Whereas most reagents seem to be unsuited to the preparation of acid halides of a-keto acids, dichloromethyl methyl ether is successful in this reaction (equation 10). Pyruvyl chloride can now be made in ca. 50% yield. In some examples the corresponding a,a-dibromomethyl methyl ether has also been tested. ... 

K. Bock, C. Pedersen, and P. Rasmussen, Reactions of acylated pentoses and acylated methyl pentosides with dibromomethyl methyl ether. Preparation of bromo-deoxy-pentoses, J. Chem. Soc., Perkin I, (1973) 1456-1461. 

K. Bock, C. Pedersen, and P. Rasmussen, Reaction of esters with dibromomethyl methyl ether, Acta... 

K. Bock and C. Pedersen, Reaction of sugar derivatives with dibromomethyl methyl ether formation of bromodeoxy compounds, Carbohydr. Res., 73 (1979) 85-91. 

Bromo-2-deoxy-3-0-formyl-tt-D-quinovosyl bromide (32) has been obtained by the reaction of dibromomethyl methyl ether (DBE) with the blocked rhamnose derivative (33). Reaction of the 4--hydroxy analogue of (33) with DBE-zinc bromide gave the pyranosyl and furanosyl bromides (34) and (35), whereas the 4-0-benzyl analogue underwent stepwise reactions via the <-glycosyl bromide, the 4- -formyl ester, and cleavage of the isopropylidene acetal to yield finally the dibromide (34) Treatment of the digitoxose tri-... 

Thiem [3] introduced the use of 2-bromo-2-deoxy-a-D-glucopyranosyl bromides 96 for the P-selective glycosylation of complex aglycones involved in aureolic acid antibiotics. These bromides were prepared by the reaction of dibromomethyl methyl ether [67] with a methyl 2,3-0-isopropylidene-a-D-mannopyranoside 95 and gave predominantly (P a 10 l) 2-deoxy-2-bromo-P-glucopyranosides in their silver triflate-promoted reactions with sugar alcohols. Radical debromination afforded the 2-deoxy-P-glycosides 97 in excellent yields (Scheme 23). 

---