A-2-Thiazoline-4-One and Derivatives

As the polarity of the medium is increased 3-alkylrhodanine (161) is obtained (389, 393). 2-Thiophosphonyl derivatives have been obtained by a similar reaction (394). 

Most of the 5-unsubstituted compounds are particularly reactive, and special care must be taken during their synthesis (386). Thus the synthesis of 2-phenyl-/i-2 thia2oline-4-one has been claimed several times, and 

Goto et al. (386) have qualitatively studied the relationship between the structure and the ease of formation of some 2-aryl- and 2-heteroaryl-A-2-thiazolin-4-one derivatives. It is found that 2-pyridyI, 2-benzimidazoyl, and 2- 6 hydroxy-5 -methyl)-benzothiazolyl derivatives are too unstable to be isolated. 6 -Hydroxy-, 6 -methyl-, and unsubstituted 2-benzothiazoiyl derivatives, as well as naphtothiazolyl derivatives are unstable but isolable. On the other hand, 6 -methoxy-. 6 -acetoxy-. and 5, 7 -dimethyl-6 -hvdroxybenzothiazolyl derivatives as well as most of their 5-methyl substituted derivatives are stable and easily prepared. 

A very active field of A-2-thiazoline-4-one chemistry concerns 2-(6 -hydroxybenzothiazol-2 -yl)-4-hydroxythiazole (171). which has appeared under the names firefly decarboxy-ketoluciferin (401, 402) and firefly oxyluciferin (403). This later name is now commonly used (404). 

fireflv oxyluciferin was successfully synthesi2ed (403. 408) and has been isolated and identified in firefly lanterns (luciola cruaciata) after the lanterns were treated with pyridine and acetic anhydride to prevent decomposition (409). In 1972, Suzuki and Goto firmly established that oxyluciferin is involved in the bioluminescence of firefly lanterns and in the chemiluminescence of firefly luciferin (403. 410).. A. mechanism involving a four-membered ring cyclic peroxide has been proposed for the reaction (406. 411). However, it was not confirmed by 0 -labelinE experiments (412). 

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