Effect of additives on the stereochemical integrity and reactivity of alpha-alkoxycarbonyl alkenylcopper intermediates. Optimal conditions for the synthesis of isomerically pure tetrasubstituted alkenes.
A systematic study on the effect of additives on the isomerizability of 1-alkoxycarbonyl alkenylcopper(I) intermediates revealed that the lithium chelator 12-crown-4 is significantly more efficient than HMPA at retarding isomerization. On the other hand, 12-crown-4 alone is unable to promote effective coupling with alkyl halides. The combination of 12-crown-4 and a reduced amount of HMPA, however, led to an improved procedure for the preparation of useful, isomerically pure tetrasubstituted alkenes such as allylation reagents and skipped dienes.
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Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
Hall
Dennis G
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