ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Reactions of stabilized ylides with aldehydosugars: influence of some factors, particularly the structure of the aldehydosugar, on the ratio of the geometrical isomers formedAldehydosugars bearing no cis-substituent on the C-atom β to the carbonyl group (2, 3, 6, 7) or bearing a substituent without an electron lone-pair (5) gave, upon treatment with acetylmethylidenetriphenylphosphorane, exclusively the E-isomer, this representing the classical behaviour of aldehydes. On the other hand, aldehydosugars having a lone-pair bearing substituent (1, 4, 8, 9) gave a mixture of E- and Z-isomers. In the case of most of the aldehydosugars of the latter type (giving some Z-isomer) a partial epimerization of the C-atom α to the carbonyl group took place when the solvent of the Wittig reaction was HCONMe2. It is probable that the presence of an electron lone-pair in the adequate position inhibits the reversion of the kinetic erythro-betaine, allowing the formation of the Z-isomer and, in particular solvent conditions, a cycloelimination leading to the epimeric aldehydosugar which ultimately reacts to give the epimeric E-enone.
Additional Material:
3 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19790620707
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