Selective Hydrogenation of Cyclic alpha,beta-unsaturated ketones containing sulfur atom with the Wilkinson type Catalyst.

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The hydrogenation of 4-thiochromones [1], 3-benzyliden-4-thiochromanones [2] and these 1,1-dioxides [3], [4] by the Wilkinson rhodium catalyst was examined and was obtained the results as follows.1.Wilkinson catalyst is inactive for [1] and starting material was recovered nearly quantitatively except 2-methy1-4-chromone which hydrogenated to corresponding thiochromanone in Ca. 30% yield.2.The hydrogenation of 2,3-dimethy1-4-thiochromone gave the 1:1 mixture of cis- and trans-2,3-dimethy1-4-chromanone.3.The hydrogenation [3] and [4] gave the corresponding 4-thio-chromanone 1,1-dioxide in a high yield, respectively.4.The hydrogenation [2] gave the corresponding 3-benzy1-4-thio-chromanone (30-40%) along with the isomerized product (3-benzy1-4-thiochromone, 10-15%).From these results, the behavioral difference of [1] and [2], [1] and [3] in the hydrogenation with Wilkinson catalyst and a mechanism of the hydrogenation with Wilkinson catalyst was discussed.