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Synthesis of ( E )‐α , β‐Unsaturated Esters and ( Z )‐Vinyl Halides with Total or High Diastereoselectivity by Using Samarium Metal
Author(s) -
Concellón José M.,
RodríguezSolla Humberto,
Huerta Mónica,
PérezAndrés Juan A.
Publication year - 2002
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200206)2002:11<1839::aid-ejoc1839>3.0.co;2-r
Subject(s) - chemistry , samarium , diiodomethane , halide , elimination reaction , metal , organic chemistry , lithium (medication) , medicinal chemistry , samarium diiodide , metal halides , medicine , surface energy , endocrinology
A highly diastereoselective β‐elimination of 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 with aldehydes at −78 °C. The influence of the reaction conditions and the structure of the starting compounds on the diastereoselectivity of the β‐elimination reactions is discussed. A comparative study of the β‐elimination reaction with preformed SmI 2 and metallic samarium is also performed. These elimination reactions can be explained by the proposed mechanism. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)