2-substituted 4,5-oxazoledicarboxylic acid dimethyl esters

Yokoyama and co-workers described a novel thermal cyclization of the D-ribose lactoxime 0-vinyl ether 336 to the 2-substituted 4,5-oxazoledicarboxylic acid dimethyl ester 337 in excellent yield (Scheme 1.91). When the authors extended this methodology to other sugar lactoxime O-vinyl ethers, they found this rearrangement was accompanied by some epimerization at C-2 or suffered from low yields. 

Although the rearrangement was initially identified in sugar substrates it is very general. For example, the lactoxime O-vinyl ethers 345 were synthesized in two straightforward steps from thiolactones 344. Thermolysis of 345 effects rearrangement to afford a series of 2-substituted-4,5-oxazoledicarboxylic acid dimethyl esters 346 from monocyclic precursors (Scheme 1.93). Additional examples of 2-substituted-4,5-oxazoledicarboxylic acid dimethyl esters available via this methodology are shown in Table 1.27. 

TABLE 1.27. 2-SUBSTITUTED-4,5-OXAZOLEDICARBOXYLIC ACID DIMETHYL ESTERS FROM CYCLIZATION OF LACTOXIME 0-VINYL ETHERS"... 

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See also in sourсe #XX -- [ , , ]

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