Elimination in Unsaturated, Hexopyranoid Systems

Only a few experiments have been reported on j8-elimination of unsaturated hexopyranuronates. Methyl 4-0-acetyl-2,6-anhydro-5-deoxy-3-0-(methylsulfonyl)-D-Zt/xo-hex-5-enonate (178) was treated with alkali-metal hydroxide in methanolic solution, as in the experiments on saturated hexopyranuronates already described. The unsaturated pyranuro-nate 179, bearing a parallel-oriented, enol ether double bond, proved, however, to be unstable. Only dark, polymeric products were obtained. The dienol ether (179) (methyl 4-0-acetyl-2,6-anhydro-3,5-dideoxy-D-gZycero-hexo-2,5-dienonate) is, like the 4H-pyran, highly unstable at room temperature. 

It is interesting that pyranoid systems having a cross-oriented, dienol ether linkage proved to be stable under the same conditions. Such a 

The dienol ether 181 has an endo- and an exo-cyclic double bond which are cross-oriented to each other as shown in 183. The alkaline cleavage of the acetate groups led to the diol 182, which also proved stable. The dienol ethers 181 and 182 show u.v. and Cotton-effect maxima (see Fig. 4). 

/3-Elimination and Double j8-Elimination in Activated, Vinylog Systems 

Similar vinylog -elimination was observed on pyranoid and furanoid sugar derivatives. Perlin and coworkers described a double j8-elimina-tion on 2,3,4,6-tetra-O-acetyl-a-D-mannopyranose by treatment with methyl sulfoxide activated by sulfur trioxide-pyridine-triethylamine. 

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