CYCLIC-KETONES VIA THE REACTION OF DITHIOLS WITH 1,3-DICHLOROACETONE - AN UNEXPECTED BASE-CATALYZED REARRANGEMENT OF ALPHA,ALPHA'-DITHIA KETONES

The reaction of dithiols with 1,3-dichloroacetone under high dilution and catalyzed by cesium carbonate in DMF affords macrocyclic ketones in good yield. Examples of functionalized cyclophanes prepared in this way include 10, 15, 16, 19, 21, and 24. With NaOMe/MeOH as the base, dithiol 14 gave ring-contracted ketone 17 in low yield, in addition to the expected 15 and 16. Ketone 17 was the sole product, in good yield, from 14 and 1,1-dichloroacetone. NaOMe/MeOH also brought about the novel ring contraction of 10 to 11 and 11 to 12. X-ray structures of 10,12,16,19, and 21 are briefly described. Possible mechanisms for the formation of 17 from 14 and for the rearrangement of 10 --> 11 --> 12 are discussed.