A detailed investigation of the enolization of ketones with ethylenechloroboronate ( ECB ) in the presence of a tertiary amine and the subsequent aldol condensations of these boron enolates was conducted. The enolization with ECB- DPEA system was found to be regioselective except for the case of butanone. The stereochemistry of the enolates derived from ethyl ketones was defined as Z on the basis of 1H-NMR comparison to the Z enolates obtained by a stereodefined route. A mechanistic model for the enolization is proposed to explain the enolization selectivity. E enolates were found to be more reactive than the Z enolates. The product aldol stereochemistry ( syn ) was correlated to the enolate geometry via a chairlike transition state ( Z enolates ) or via a boatlike transition state ( E enolates ). © 1984.
Stereoselective aldol condensations via alkenyloxy dialkoxyboranes : mechanistic and stereochemical details / C.M.A. Gennari, L. Colombo, C. Scolastico, R. Todeschini. - In: TETRAHEDRON. - ISSN 0040-4020. - 40:20(1984), pp. 4051-4058.
Stereoselective aldol condensations via alkenyloxy dialkoxyboranes : mechanistic and stereochemical details
C.M.A. Gennari;C. Scolastico;
1984
Abstract
A detailed investigation of the enolization of ketones with ethylenechloroboronate ( ECB ) in the presence of a tertiary amine and the subsequent aldol condensations of these boron enolates was conducted. The enolization with ECB- DPEA system was found to be regioselective except for the case of butanone. The stereochemistry of the enolates derived from ethyl ketones was defined as Z on the basis of 1H-NMR comparison to the Z enolates obtained by a stereodefined route. A mechanistic model for the enolization is proposed to explain the enolization selectivity. E enolates were found to be more reactive than the Z enolates. The product aldol stereochemistry ( syn ) was correlated to the enolate geometry via a chairlike transition state ( Z enolates ) or via a boatlike transition state ( E enolates ). © 1984.Pubblicazioni consigliate
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