- Photoaddition of N-acylbenzoxazole-2-thiones to alkenes
-
N-Acylbenzoxazole-2-thiones 1 undergo photoaddition with alkenes 2 in a regiospecific manner to yield benzoxazole derivatives 3-9 and/or the unexpected, iminothietanes 10-14 via spirocyclic aminothietane intermediates, depending on the nature of the substituents both on the N-atom of 1 and those present in the alkenes 2.
- Nishio, Takehiko
-
-
Read Online
- Photocycloaddition reactions of alkyl and aryl 2-thioxo-3H-benzoxazole-3-carboxylates to Alkenes
-
The photochemical reactions of alkyl and aryl 2-thioxo-3H-benzoxazole-3-carboxylates 1 have been examined. Irradiation of 1 in the presence of tetra- and trisubstituted alkenes 2a and 2b, 2-methylprop-2-ene nitrile 2e, and dienes 2f and 2g gave [2+2] cycloadducts of the C=S bond of 2-thioxobenzoxazoles and the C=C bond of alkenes, spiro[benzoxazole-thietanes] 3, 4, 8-13, 15, 18, 20, 23-26 in moderate- to-good yields. The photoaddition reactions proceed in a regiospecific manner. The spirocyclic compounds obtained are indefinitely stable at room temperature. Irradiation of 1a in the presence of 1,1- and 1,2-disubstituted alkenes 2c and 2d yielded the products 5-7 of oxazole-ring cleavage. Compound Id also underwent photoaddition with alkenes to yield spiro[benzoxazole-thietanes] and/or 2-substituted benzoxazoles and/or iminothietanes, depending on the nature of the substituents present in the alkenes. On intramolecular [2 + 2] photoadduct, tetracyclic 27, was obtained, when ethenyl 2-thioxobenzoxazole-3-carboxylate 1e was irradiated.
- Nishio, Takehiko,Shiwa, Kiyoko,Sakamoto, Masami
-
p. 2383 - 2393
(2007/10/03)
-
- Photochemical reactions of N-acylbenzoxazole-2-thiones
-
The photochemical reactions of N-acylbenzoxazole-Z-thiones 1 are examined. Irradiation of N-acylbenzoxazole-2-thiones 1 in the presence of a variety of alkenes 2 yields 2-substituted benzoxazoles 3-20 and/or the unexpected products, iminothietanes 21-29 by intramolecular trapping of the acyl group by thiolate anion of the zwitterionic intermediate I and by the phenolate anion of the zwitterionic intermediate II, respectively, derived from the spirocyclic aminothietanes AT which are formed by regioselective [2+2] cycloaddition of the carbon-sulfur double bond of 1 to the alkene double bond. The Royal Society of Chemistry 2000.
- Nishio, Takchiko,Iida, Ikuo,Sugiyama, Kunjo
-
p. 3039 - 3046
(2007/10/03)
-