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Communication | Special issue | Vol 86, No. 1, 2012, pp.117-126
Published online, 13th July, 2012
DOI: 10.3987/COM-12-S(N)17
SULFUR- AND N-ACYL CARBONYL OXYGEN-ASSISTED HETEROLYSIS OF THE C(=O)–S BOND IN EXCITED-STATE (Z)-N-ACYL-α-DEHYDRO(1-NAPHTHYL)ALANINE THIOESTERS

Yosuke Hosoi, Tetsutaro Igarashi, and Tadamitsu Sakurai*

*Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan

Abstract

Irradiation of the title thioesters (Z)-1 in nitrogen-saturated 1,2-dichloroethane at wavelengths greater than 280 nm was found to afford (Z)-4-(1-naphthylmethylene)-5(4H)-oxazolone derivatives (Z)-2, (E)-2, alkyl-substituted thiols 3, and (E)-1 without forming any thio-radical-derived products. An analysis of the substituent and solvent effects on the reactivity of 1 and the product distribution demonstrated that the heterolytic C(=O)–S bond cleavage products 2 and 3 are not derived from the long-lived acylium and thiolate ions but from the protonated oxazolone/thiolate ion pair. The latter intermediates were assumed to be formed by the sulfur-assisted nucleophilic addition of the N-acyl carbonyl oxygen to the thioester carbonyl carbon in the excited state, followed by the elimination of the thiolate ion from the resulting adducts.