The reaction of a,b-chalcone ditosylates 3 with potassium hydroxide in suitable conditions leads to 1,2-aryl shift and carbon-carbon bond cleavage, thereby providing a novel route for the synthesis of 1,2-diarylethan-1-ones 4 and 1,2-diaryl-3,3-dimethoxy propan-1-ones 5.A great deal of work from our research group and others has emphasized the advantages of a-tosyloxyketones over a-haloketones in various chemical transformations. 1,2 On the other hand while chemistry of a,b-chalcone dibromides 2 is well explored, 3 the study pertaining to reactivity mode of a,b-chalcone ditosylates 3 has remained an uncharted territory. These observations coupled with our ongoing program on advantageous use of a-tosyloxyketones over a-haloketones prompted us to investigate the reactivity pattern of a,b-chalcone ditosylates 3 in comparison with a,b-chalcone dibromides 2. As a consequence of our initial efforts, we wish to report novel routes for the synthesis of 1,2-diarylethan-1-ones 4 and 1,2-diaryl-3,3-dimethoxy propan-1-ones 5 by the reaction of a,b-chalcone ditosylates 3 with potassium hydroxide in suitable conditions. Thus, various derivatives of a,b-chalcone ditosylates 3a-3j were prepared by the treatment of respective chalcone 1 with [hydroxy(tosyloxy)iodo]benzene (HTIB) 4 according to the method of Koser (Scheme 1, Table 1). 5,6
Scheme 1We first examined the reaction of a,b-chalcone ditosylates 3 with potassium hydroxide according to the conditions described for the elimination of a,b-chalcone dibromides 2 (Scheme 2). 3b
Scheme 2Thus, 3a was treated with two equivalents of potassium hydroxide in ethanol under reflux for about 2-3 hours. The workup of the reaction did not afford any elimination product. Instead, a 1,2-aryl shift, followed by carbon-carbon bond cleavage occurred with the formation of 1,2-diphenylethan-1-one (4a) in 58% yield. Under the same conditions, other derivatives 3b-3j also afforded 1,2-diarylethan-1-ones 4b-4j in 60-68% yields (Scheme 3, Table 2). 7To study the effect of reaction conditions, solvents, etc., a series of experiments was performed on the substrate 3a with potassium hydroxide under different conditions. These experiments showed that the conversion 3a → 4a