Polarized ketene dithioacetals. Part 42. Studies on the reactions of alkyl and aryl Grignard reagents with α-oxoketene dithioacetals

Abstract

The oxoketene dithioacetals (2a-k) derived from a variety of cyclic and acyclic active methylene ketones undergo 1,2-addition with methylmagnesium iodide to give the alcohol acetals (3a-k) which, on subsequent boron trifluoride-ether catalysed methanolysis, yield methyl β -methyl-α,β-unsaturated esters (6a-k) in 51-70% overall yields. Also the alcohols (3a) and (3i-k) underwent partial hydrolysis in the presence of boron trifluoride-ether and water to yield β-methyl-α,β-unsaturated S-methyl esters (7a-d) in 41-60% yield. Under similar conditions however, the oxoketene dithioacetals (21-q) derived from higher homologues of acetophenone yielded the corresponding 2-alkyl-3-methylinden-1-ones (8a-f) in 50-62% overall yields. The reactions of cyclic oxoketene dithioacetals (2g), (2h), and (2j) with higher alkyl Grignard reagents afforded the alcohols (13a-f), formed by sequential 1,4 and 1,2 addition, which on subsequent methanolysis yielded the corresponding 1-(2-alkylcycloalk-1-enyl)alkan-1-ones (14a-f) in 48-58% overall yields. Similarly the phenylmagnesium bromide underwent sequential 1,4 and 1,2 addition to the oxoketene dithioacetals (2a-c), (2h) and (2j) to yield the alcohols (13g-k), which upon subsequent methanolysis yielded either 1,3,3-triarylprop-2-en-1-ones (14g-i) or phenyl (2-phenylcycloalk-1-enyl) ketones (14j-k) in 53-71% yield.