TMSOTf-catalyzed isomerization of acetates of the Baylis-Hillman adducts, i.e. methyl 3-acetoxy-3-aryl-2-methylenepropanoates and 3-acetoxy-3-aryl-2-methylenepropanenitriles pro-viding methyl (2E)-2-(acetoxymethyl)-3-arylprop-2-enoates and (2E)-2-(acetoxymethyl)-3-arylprop-2-enenitriles, respectively, is described.

The titanium tetrachloride mediated reaction of alpha-keto esters with 5,5-dimethylcyclohex-2-enone provides the corresponding Baylis-Hillman adducts exclusively whereas a similar reaction of alpha-keto esters with cyclohex-2-enone furnishes the corresponding aldol adducts (with high syn-diasteroeselectivity) as the major product (along with the Baylis-Hillman adducts as the minor product), thus clearly demonstrating the role of the steric factors in directing the reaction pathway.

No abstract

The Baylis-Hillman reaction of a-keto esters with a,bunsaturated ketones under the catalytic influence of dimethyl sulfide in the presence of titanium tetrachloride leading to the formation of 2-aryl-2-hydroxy-3-methylene-4-oxoalkanoates has been described.The Baylis-Hillman reaction is an emerging carbon-carbon bond forming reaction involving the coupling of activated alkenes with carbon electrophiles under the catalytic influence of tertiary amines (particularly DAB-CO) producing a novel class of multifunctional molecules and is of current interest. [1][2][3][4][5][6][7][8][9][10][11][12][13] In continuation of our interest in the development of the Baylis-Hillman reaction, 8-13 we herein report dimethyl sulfide catalyzed coupling of aketo esters with methyl vinyl ketone and ethyl vinyl ketone in presence of titanium tetrachloride thus providing a simple and convenient methodology for synthesis of 2-aryl-2-hydroxy-3-methylene-4-oxoalkanoates.The Baylis-Hillman reaction of a-keto esters with activated alkenes such as acrylates and acrylonitrile providing densely functionalized products with a quaternary carbon centre and the applications of these molecules in organic synthesis have been well documented in the literature. 14-18 During our work on the ongoing research program on the Baylis-Hillman reaction we required 2-aryl-2-hydroxy-3-methy-lene-4-oxoalkanoates. A literature survey reveals that Golubev and coworkers reported the DABCO catalyzed coupling of methyl vinyl ketone (mvk) with methyl trifluoropyruvate to provide methyl 2-hydroxy-3-methylene-4-oxo-2-trifluoromethylpentanoate in high yield. 17 However, our attempts to synthesize ethyl 2-hydroxy-2-phenyl-3-methylene-4-oxopentanoate via DABCO catalyzed coupling of methyl vinyl ketone with ethyl phenylglyoxylate (a-keto ester) were unsuccessful. 19 Recently Kataoka et al. 20,21 reported an interesting chalcogenoBaylis-Hillman reaction of aldehydes with different a,bunsaturated ketones in the presence of Lewis acid to provide the desired a-hydroxyalkylated enones in moderate to good yields. With a view to providing a convenient synthesis of 2-aryl-2-hydroxy-3-methylene-4-oxoalkanoates and also with a view to expanding the scope of chalcogeno-Baylis-Hillman reaction we have examined the possibility of coupling a, b-unsaturated ketones with a-keto esters under the catalytic influence of dimethyl sulfide in the presence of Lewis acid. During our studies in this direction, we have first carried out the reaction of ethyl phenylglyoxylate with methyl vinyl ketone (mvk) under various conditions. The best results were obtained when ethyl phenylglyoxylate (1) was treated with methyl vinyl ketone and a catalytic amount of dimethyl sulfide in the presence of titanium tetrachloride in dichloromethane at room temperature for one hour thus providing the desired ethyl 2-hydroxy-2-phenyl-3-methylene-4-oxopentanoate (6) in 73% yield. 22 Encour-aged by this result we have carried out the coupling reaction of representative a-keto esters 2-5 with methyl vinyl ketone (mvk) unde...

No abstract