Thiazoline-2-thione, reaction with acetate

Thiazolo-[4,5-d]- and -[5,4-d]-pyrimidines [C3NS-C4N2]. The reaction of the A" -thiazoline (139) with NaSH or with H2S and pyridine gives the thiazolo-[4,5-i/]pyrimidine-7-thione (140 R = Ac, R = H, X = S), and with acetic anhydride and PPA yields (140 R = H, R = Me,X = O), whilst the readily available ethyl 2-methylmercapto-5-aminothiazole-4-carboxylate will react with formamide to give the thiazolo[5,4- f]pyrimidin-4-one (141). ... 

Alkylation Reactions.—The mechanism proposed for the conversion of benzo-thiazoline-2-thione (29 R = CH2CH2OH, X = S) into the corresponding benzothiazolin-2-one (29 X = O) with ethylene oxide in acetic acid is considered to involve ring-opening by the thione sulphur atom to give the j8-sub-stituted ethanol. This reacts with acetate ion or acetic acid at the 2-position to give an acetate, which decomposes to MeC(0)SCHaCH20H and (29 X = O). In support of the mechanism, no desulphurization occurred when the reaction was attempted in acetone or methanol. 

Equimolar quantities of acetylenedicarboxylic acid esters (166) and 2-N-substituted l,3-dithiolan-2-imines (169) undergo a 1,3-dipolar cycloaddition, with elimination of ethylene, to yield A -thiazoline-2-thiones (168). The same products result from 2-alkylthio-l,3,4-thiadiazoline-5-thiones (167), with loss of alkyl thiocyanate as shown. They are desulphurized to the corresponding thiazolinones (172) by the action of mercuric acetate in acetone-acetic acid. They react with two further moles of the acetylenic reagent (166) to produce the spiranes (170 e.g. = R = COzMe), which are in turn desulphurized and cleaved by Raney nickel to the AMhiazoline derivatives (171). An analogous series of reactions was carried out using propiolic acid esters. ... 

If, however, the cyclization reaction is carried out in the presence of hydrochloric acid, the reaction product is 3 rniiio-4-methyl-5-ethoxycarbonyl-J4-thiazoline-2-thione (m.p. 76—7° C). In basic medium the ring closure reaction of ammonium dithiocarbazate with the ethyl-a-chloroacetyl acetate occurs at the ethoxycarbonyl group with formation of 3-amino-5-acetylthiazolidin-4-one-2-thione (303). 

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