PHOTOCHEMICAL RING CLOSURE OF α,α-BISULFENYLATED CARBONYL COMPOUNDS STEREOSELECTIVE FORMATION OF CIS-DIHYDROBENZOTHIOPHENES

Article abstract of DOI:10.1016/0040-4020(82)85048-5

Photochemistry of α,α-bisulfenylated ketone has been investigated.Irradiation of 2-phenylthiodihydrothiophen-3-one (1) in benzene gave the radical recombination products 9 (63percent) and 10 (49percent).In a polar solvent, the ionic chemistry became predominant.Brief irradiation of 1 in acetonitrile and methanol gave the cis-fused dihydrothiophene 11 as the major product in 43percent and 20percent yields, respectively.The stereoselective photocyclization was generally observed for other ketones (2-8) in acetonitrile solution (Table 1).The photoproducts were easily dehydrated by treating with boron trifluoride etherate to give the corresponding benzothiophenes in high yields.Simple α-phenylthioketones are photoinert under the same conditions.The mechanism of this novel photocyclization of bisulfenylated ketones is also discussed.