The photochemistry of cyclic nonenolizable α-diketones and ketones influence of remotely positioned sulfide,sulfone, and sulfoxide functionalities

The photochemistry of 3,3,6,6-tetramethyl-1-thiacycloheptane-4,5-dione has been examined along with that of the corresponding S-oxide and S,S-dioxide. The chief photochemical process in the first mentioned compound is ring contraction affording 3,3-dimethyl-1-thia-cyclobutan-2-one, isobutene, and carbon monoxide. In addition a small amount of 3,3,6,6-tetramethyl-1-thiacyclohexan-4-one is formed along with two isomeric unsaturated aldehydes. On independent irradiation this thiacyclohexanone affords the same products as its 7-membered diketone counterpart. Similar products are obtained for the S-dioxides investigated save that the ring contraction process was absent. The S-oxides gave no identifiable products. All the results are rationalized in terms of a generalized mechanism involving biradical intermediates.