Photochemical ring closure of α,α-bisulfenylated carbonyl compounds: Stereoselective formation of cix-dihydrobenzothiophenes |
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Authors: | Tadashi Sasaki Kenji Hayakawa Sumio Nishida |
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Institution: | Institute of Applied Organic Chemistry, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464, Japan |
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Abstract: | Photochemistry of α,α-bisulfenylated ketone has been investigated. Irradiation of 2-phenylthiodihydrothiophen-3-one (1) in benzene gave the radical recombination products 9 (63%) and 10 (49%). 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 43% and 20% yields, respectively. The stereoselective photocyclization was generally observed for other ketones (2–8) in acetonitrile solution (Table 1). The photo-products 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. |
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