An efficient synthesis of (E)-α,β-unsaturated ketones and esters with total stereoselectivity by using chromium dichloride
作者:José M. Concellón、Humberto Rodríguez-Solla、Carmen Méjica
DOI:10.1016/j.tet.2006.01.052
日期:2006.4
(E)-α,β-Unsaturatedketones 1 or esters 2 can be obtained with complete stereoselectivity by reaction of different 2-chloro-3-hydroxy ketones 3 or esters 4 and CrCl2. A comparative study of the results of synthesis of ketones 1 with CrCl2 or samarium is performed. A mechanism to explain both β-elimination reactions has been proposed.
2-halo-3-hydroxy esters 1 or O-acetylated 1,1-dihaloalkan-2-ols 4 is achieved with samarium in the presence of diiodomethane, yielding α,β-unsaturated esters 2 or vinyl halides 5, respectively. The β-elimination reaction was promoted by samarium diiodide, which was generated in situ. The starting halohydrins 1 or 4 are easily prepared by reaction of the corresponding lithium enolates of α-halo esters or dihalomethyllithium
Synthesis of (E)-α,β-unsaturated esters in high yields and with total stereoselectivity is achieved from α-halo-β-hydroxy esters promoted by catalytic amounts of SmI2. The starting compounds were easily prepared from α-halo esters and aldehydes as a mixture of stereoisomers. A mechanism is proposed to explain this samarium(II)-promoted catalytic β-elimination reaction.
Synthesis of 2,3-dideuterioesters from 2-halo-3-hydroxyesters by using metallic samarium and diiodomethane
作者:José M Concellón、Mónica Huerta
DOI:10.1016/s0040-4039(02)00950-4
日期:2002.7
2,3-Dideuterioesters are obtained in high yield from 2-chloro-3-hydroxyesters by a sequenced elimination;reduction process promoted by samarium diiodide generated in situ from metallic samarium and diiodomethane. (C) 2002 Elsevier Science Ltd. All rights reserved.