Phenyl-2-thiophenyl ketone

Scheme 4. Synthesis of Phenyl-2-thiophenyl Ketone (12) Reaction of Benzoyl Chloride (14) with Thiophene (13)...

The yeast-induced reduction of (5e) —> (6e), (R = substituted phenyls, R = Me) is one of the very first preparative-scale alcohol dehydrogenase catalyzed reactions to have been reported. While the transformations of (5a-j) demonstrate that broad structural mlerances are possible in the substrate ketones, the enzymes are sometimes very discriminating. For example, while the BY-catalyzed reductions of the 2-, 3- and 4-substituted pyridyl ketones (5g) proceed smoothly with high stereospecificitythe analogous furanyl and thiophenyl ketones give virtually racemic product alcohols, and 2-acetylpyrrole is not a substrate at all. ... 

Kinetic and thermodynamic measurements show that 2-phenylacetylthiophene (92a) has a low enol content K = 3.55 x 10 7 (or )K = 6.45).136 The keto and enol tautomers have pKa values of 14.60 and 8.15, respectively. Relative to a phenyl or furanyl substituent at the carbonyl carbon, the thiophene increases the acidity of the enol tautomer, but stabilizes the ketone, probably via the resonance contribution (92b). Thus 2-thiophenyl stabilizes the enolate by electron attraction, but the ketone by donation. Effects of micelles on the equilibria are also reported. 

As shown in Scheme 7.14, these metal compounds act as catalysts because these cyclometalation products are highly reactive and react easily with other reagents. The substrates of these reactions are not only aromatic compounds, such as methyl phenyl ketone (Eq. (7.50)) [100,101,103] and phenylimine (Eq. (7.51)) [100,103], but also nonbenzenoid compounds, such as thiophenyl methyl ketone (Eq. (7.52)) [100,101] and cyclohexenyl methyl ketone (Eq. (7.53)) [103]. 

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