3- -4-hydroxy-1 -thiocoumarin

Toda et al. reported that the topotactic and enantioselective photodimerization of coumarin and thiocoumarin takes place in single crystals without significant molecular rearrangements [49]. Molecular motion needs to be called upon to explain the photochemically activated cycloaddition reaction of 2-benzyl-5-benzylidenecyclopentanone. The dimer molecules, once formed, move smoothly in the reactant crystal to form the product crystal [50]. Harris et al. investigated the reactivity of 10-hydroxy-10,9-boroxophenanthrene in the solid state and the mechanism of the solid-state reaction was characterized by both X-ray diffraction and thermal analysis [51]. It was demonstrated that the solution chemistry of 10-hydroxy-10,9-boroxophenanthrene is different from that in the solid state, where it undergoes dimerization and dehydration to form a monohydride derivative. 

Apart from the chemistry of the 4-hydroxy derivative (see p. 126) relatively little investigation in this area has been conducted. Thiocoumarin-3-carbonyl compounds have proved to be effective precursors for the synthesis of the pharmaceutically useful 3-(2-benzimidazolyl) derivatives. Thus, on interaction of the 3-carboxamide with o-phenylenediamine or the 3-aldehyde with o-nitroanilines, the above benzimidazoles or their TV-oxides are formed. 

By far the most studied derivative of thiocoumarin is the 4-hydroxy compound (26), partly due to its ease of preparation and to some extent to its potential as a source of biologically significant derivatives. Thus, the thio analog (27) of the rodenticide Warfarin was examined, but showed only... 

Thiocoumarin reacts with phenylmagnesium bromide to give a mixture of 2-phenyl-A -thiochromene and thioflavone, the latter product being presumed to arise by oxidation of 4-hydroxy-2-phenyl-A -chromene, formed via a thiopyrylium cation. 4-Hydroxythiocoumarin has been acetylated at the 3-position, by treatment with acetic acid and phosphorus oxychloride reactions of the product with amines and with phenylhydrazine have been studied. ... 

Benzisothiazoles.—Synthesis. A number of 1,2-benzisothiazole-3-acetic acids (128) have been prepared with the aim of studying their potential activity as plant hormones. They were produced, usually in near-quantitative yields, by the action of hydroxylamine on substituted 4-hydroxy-l-thiocoumarins (127) (c/. ref. 56). 5-Chloro-l,2-benzisothiazole-3-acetic acid proved very potent, possessing an activity about three times that of of heteroauxin. ... 

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