B. G. Advani

Synthesis of 1,1-diamino-2-thioacylethylenes: A novel C-thioacylation by the Willgerodt-Kindler reaction

Abstract A novel C -thioacylation reaction is described. Reaction of aromatic or heterocyclic aldehydes with 1-alkyl-2-methyl-1,4,5,6-tetrahydropyrimidine or 1-alkyl-2-methylimidazolidine in the presence of sulphur leads to the thioacylketeneaminals 6 , 10 or 12 in low to moderate yields. The structure of 6e was proved by S -methylation to 7e and acid-hydrolysis to the known 8e . Oxidative cyclization of 6 leads to the isothiazolo[2,3- a ] pyrimidinium salts 13 .

A general synthesis of thiazoles. Part 3. Comparative evaluation of different functionalised thioureas as precursors

N-Acyl-N′-monosubstituted thioureas (9) react with phenacyl bromide to produce thiazolines (10) and not thiazoles (4), as claimed. The addition products of N-arylbenzamidines and phenyl isothiocyanate react with phenacyl bromide to give 2-anilino-5-benzoyl-4-phenylthiazole (4a). The adduct (11) of methyl benzimidate and phenyl isothiocyanate yields thiazoles (4a) and (12) by reaction with phenacyl bromide and bromonitromethane, respectively.

c-Thioacylation by the Willgerodt–Kindler reaction. Structure of the anomalous products from salicylaldehydes. X-Ray crystal structure of the betaine from 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, sulphur, and 3,5-dichlorosalicylaldehyde

1,2-Dimethyl-1,4,5,6-tetrahydropyrimidine (1), on reaction with salicylaldehydes (3) in the presence of sulphur, does not lead to the expected C-thioacylated products (4); instead, the products obtained are the betaines (5). The structure of (5b) from 3,5-dichlorosalicylaldehyde has been established by X-ray diffraction analysis.

4-Acetyl-3-benzylidenepiperazine-2,5-diones

Cyclisation of (N-acetyldidehydrophenylalanyl)sarcosine with acetic anhydride at 75° has furnished the hitherto unknown 4-acetyl-3-trans-benzylidene-1-methylpiperazine-2,5-dione (IV), which readily undergoes deacetylation on treatment with morpholine.

A novel ring-opening of a 2-alkyl-5-imino-4-nitro-2,5-dihydroisothiazole by cyanide ion

Reaction of 2-methyl-3-methylamino-4-nitro-5-phenylimino-2,5-dihydroisothiazole (1b) with cyanide ion proceeds with two successive sequences of ring-opening and ring-closure with the ultimate generation of 2,5-bis(methylamino)-4-nitro-3-phenylimino-3H-pyrrole (2b) or its tautomer (2a).

Unexpected substitution of the acyl group in isothiazole-ring formation. Attempted conversion of 1-acyl-2,2-diaminoethylenes into 2-acyl-3,3-diaminoacrylonitriles

2-(Acylmethylene) hexahydropyrimidines (7) have been converted into the corresponding benzoyl isothiocyanate adducts (8), treatment of which with sulphuryl chloride gave the 3-chloroisothiazolo[2,3-a]pyrimidine (10) instead of the expected 3-acyl compound (9). Oxidation of the adduct (8c) by bromine gave the isothiazolo[2,3-a]-pyrimidine (9c) in low yield; this failed to undergo base-catalysed fragmentation to the nitrile (13c). Finally, the α-acyl-α-cyanomethylenehexahydropyrimidines (13) were prepared from the phenacyl- and 2-thenoylmethyl-cyanides (11) by condensation with 1-methyl-2-methylthio-1,4,5,6-tetrahydropyrimidine (12).

Conformational studies on tricyclic quinazolones derived from cyclodipeptides incorporating sarcosine.

Ring C of the tricyclic quinazolone 2-methyl-1,2-dihydropyrazino[2,1-b]quinazoline-3(4H),6-dione (VII) has conformational flexibility. However, introduction of a 4-methyl group as in (IX) locks the molecule in the conformation in which the 4-methyl group is axial.