4970
Reductive Acylation of Ketones. I1 l V 2 Leonard Kaplan
Contribution f r o m the Department of Chemistry, University of Chicago, Chicago, Illinois 60637. Receiced June 15, 1966 Abstract: Some ketone-to-ester conversions brought about in high yield under neutral and mild conditions are described. The reaction involves treatment of the ketone with an acid chloride and triphenyltin hydride and results in reductive acylation of the ketone.
s the start of a program designed to develop synthetic methods for t,he addition of the elements of R-H across unsaturated linkages, we recently reported some examples of the addition of RCO-H across ketone carbonyl groups. ? These ketone-to-ester conversions involved the reaction of a n acid chloride with triphenyltin hydride in the presence of a ketone and resulted in “quantitative” conversion ofthe ketone t o the desired ester. However, the method, as described, was not generally applicable, since the examples reported concerned only ketones of the type PhCOR. It is the purpose of this paper t o give a more detailed account of this work and to present some applications of the reaction t o dialkyl ketones. An account of previous work has already been
Table I. Summary of Systems Studied
Discussion of Results The reaction system consisted of acid chloride, triphenyltin hydride, and ketone in benzene as solvent. In all cases, listed in Table I, “quantitative” conversions of the ketone t o the desired ester were obtained, except in that procedure leading t o isopropyl benzoate, in which the conversion was 90%. In these systems, we have observed the following reactions: (A) reaction of all three reagents to yield the desired ester, (B) reduction of the acid chloride t o aldehyde by triphenyltin hydride, (C) reaction between the ketone and triphenyltin hydride, (D) reaction between the ketone and acid chloride. The relative rates of these reactions vary significantly from system t o system. However, in each case, it is possible t o choose reaction conditions such that reaction A predominates overwhelmingly. Examples of each type of procedure are given in the Experimental Section.
C6HsCOCI. CsH,COCH?
A
Experimental Section In all cases yields were determined by use of nmr spectroscopy and gas chromatographic analysis. Materials. Acetyl chloride, acetophenone, a-phenethyl acetate, propionyl chloride, propiophenone, isobutyrophenone, benzoyl chloride, 3-pentanone,3-carbomethoxypropionylchloride, acetone, isopropyl acetate, isopropyl benzoate, and benzene were commercial materials and were used without further purification. Triphenyltin (1) This work was supported by American Cancer Society Institutional Grant 41-F and National Institutes of Health Grant GM-1366201. ( 2 ) P a r t I : L. I
