1.3.4- Thiadiazolines, reaction with acetylenic

In a similar manner, Mloston et al. prepared the thiadiazoline 88 and treated it with electron-deficient acetylenes giving 2,5-dihydrothiophenes 89 in generally good yields. Reaction of 89 with TFA at room temperature, resulted in the formation of thiophene 90 via isomerisation and ring-opening of the cyclobutane ring <02HCA451 >. 

With activated acetylenes (27, X = PhCO, COOMe), Hector s bases yield substituted 2-arylaminothiazoles (29). The course of the reaction may be rationalized by assuming the usual intermediate heteropentalene formation (28).42 4-Alkyl-5-imino-3-methyl-A2-l,2,4-thiadiazolines (30) undergo the same type of reaction.43... 

A (1/7-imidazol-l-yl) silver species (55) has been postulated as the key intermediate in the 3-l-2-cycloaddition reaction of diazoalkanes (54) with benzynes yielding 2-aryl-2H-indazoles (56) (Scheme 18). The 3-I-2-cycloaddition reaction of 3-trifluoromethyl-4-diazopyrazolinones with dialkyl acetylene dicarboxylates, in refluxing toluene, produced spiro 3/f-pyrazole adducts that rearranged to the trifluoromethyl-substituted pyrazolo[l,5-fi(][l,2,4]triazin-7-ones. ° The 1,3-dipolar cycloaddition reaction of aromatic thioketones (58) with 2-aza-1,3-dicarbonyl compounds (57), at 20-50 C, yielded thiadiazoline adducts (59) that readily eliminate nitrogen to produce oxathioles (60) in moderate yields (up to 70%) (Scheme 19). ... 

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. ... 

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