Abstract
A synthesis of (Z)-1-alkyl-2-arylvinyl acetates 3 with broad scope is reported by using two complementary methods. The first one uses a stereospecific gold-catalyzed addition of acetic acid to 1-iodo-alkynes, followed by a Suzuki coupling. By the second, 1-methyl-2-arylvinyl substrates have been obtained selectively as the Z isomers by O-acylation of enolates of methyl benzyl ketones. In addition, the asymmetric hydrogenation of enol esters 3 has been covered for the first time. Using rhodium catalysts based on chiral phosphine-phosphite ligands (P-OP), highly enantioselective hydrogenations (up to 99% ee) have been achieved for a wide range of substrates. Thus, the synthesis and enantioselective hydrogenation of 3 provides a convenient and versatile procedure for the synthesis of valuable chiral homobenzylic esters.
Highlights
A synthesis of (Z)-1-alkyl-2-arylvinyl acetates 3 with broad scope is reported by using two complementary methods
The success of the enzymatic reduction of B strongly contrasts with the results obtained in catalytic asymmetric hydrogenations
An alternative route to alcohols A based on an asymmetric hydrogenation, which could benefits of the inherent practical advantages of this kind of reaction,[9] is based on the reduction of the olefin bond of 1-alkyl-2-arylvinyl esters C followed by a trivial deacylation.9g,l,10a,11 In a previous contribution, we described the highly enantioselective hydrogenation of 1-benzylvinyl benzoate (D), but extension of this
Summary
A synthesis of (Z)-1-alkyl-2-arylvinyl acetates 3 with broad scope is reported by using two complementary methods. Most of these alcohols are methyl carbinols, while information about the reduction of ketones with alkyl (Ak) substituents other than Me is rather scarce.[6] This factor can be of high importance because of the influence of the Ak substituent on the enantioselectivity observed in some of these enzymatic reactions.6a
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