Cyclopropylcarbinyl-oxo-carboniumions. A solvolytic basis for the cyclopropylcarbinyl-oxo-carbonium ion

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Abstract
Hydrolysis of 4,6-O-benzylidene-3-deoxy-3-C-(iodomethyl)-D-allal (1) in neutral buffered medium with or without silver ion assistance gives the cyclopropyl aldehyde 4 as the only product. Methanolysis of 1 gives an equal mixture of the α and β anomers of methyl 4,6-O-benzylidene-2,3-C-methylene-2,3-dideoxy-D-allopyranosides (6 and 7). These results indicate that the cyclopropylcarbinyl-oxo-carboniumion (2), is produced with unit efficiency in solvolyses in neutral media, and the formation of both diasteriomers (6 and 7) requires the complete absence of bicyclobutonium ion (9) resonance contribution to the stabilized intermediate, and implies a strong contribution from the oxo-carbonium ion 10. In basic media compound 1 undergoes quantitative dehydroiodination to the conjugated diene, 4,6-O-benzylidene-1,2,3-trideoxy-3-C-methylene-D-ribo-hex-1-enopyranose(8).

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