Selective double bond reduction of unsaturated conjugated ketones has been achieved in excellent yields by use of sodium dithionite in a two phase benzene-water system with Adogen as phase transfer catalyst. However, this reduction was unsatisfactory for hydrophilic ketones; in this case, competitive reactions led to the predominant formation of water soluble sulfur derivatives, similar to those obtained in the reaction of unsaturated conjugated ketones with sodium dithionite in aqueous dimethylformamide. Several reports have appeared in the literature on the application of aqueous solutions of sodium dithionite in the presence of cosolvents, such as dimethylformamide or dioxane, as advantageous alternative for reduction of aldehydes and ketones to alcohols?-4 In this context, we have extended this reduction procedure to a two phase benzene-water system by the use of phase transfer catalysts, with results comparable or even superior to those obtained under the above homogeneous conditions5 Likewise. we have also described the regiospecific reduction of 2,4-alkadienoic acids and esters with sodium dithionite to afford Z:E isomeric mixtures of the corresponding 3-alkenoic acids and -esters, respectively, in good yields. A moderate stereoselectivity (Z:E, 3:l) was observed in the -reduction of the above acids in aqueous solution, while approximately the same amounts of both isomeric monoene esters were obtained in the presence of phase transfer catalysts6 Although Chung' had claimed that a,B-unsaturated ketones were resistant to the reduction by sodium dithionite in aqueous DMF, our interest to broaden the scope of application of this reagent in general organic synthesis led us to restudy that reaction. A recent preliminary reportB along this line has prompted us to present here our detailed experimental procedure for regiospecific reduction of double bonds in conjugated unsaturated ketones with sodium dithionite under phase transfer catalysis. RESULTS AND DISCUSSION As shown in Table 1, reduction of unsaturated ketones to the corresponding dihydroderivatives was generally achieved in excellent yields, using 2.25 or g fold molar excesses of sodium dithionite in a water-benzene two phase system, containing sodium bicarbonate and a commercial mixture of methyl trialkyl [CB-CId] ammonium chlorides (Adogen 464Q). As a rule, stepwise addition of the reductant led to an improvement of the yields obtained. presumably, by avoidance of the fast