2.5- Dialkyl thiazoles, preparation

Metal Complexes.—In an extensive study of the complexing power of thiazoles, numerous zinc(n), cobalt(n), copper(ii), nickel(ii), andplatinum(n) complexes of the parent compound, and of 4-alkyl- or 2,4-dialkyl-thiazoles, usually of the general type MX2L2, have been prepared. A consideration of their spectral and magnetic properties reveals that the zinc and cobalt complexes are tetrahedral, the 4-methyl copper and nickel complexes are octahedral, and the dialkyl complexes of copper and nickel and the platinum complexes are square planar. The four-co-ordinate dialkyl complexes follow the crystal field stabilization energy predictions as to the relative tendency to form tetrahedral or square-planar forms, i.e. Zn > Co > Cu > Ni. The complexes are invariably metal-nitrogen, and not metal-sulphur, co-ordinated. ... 

B en zoylimino-3-p-nitrophen y 1-4-phen yl-A,-selenazoline, preparation, 228 acid hydrolysis, 229 Benzthieno[2,3d] thiazole, 30 Benzylidene derivatives of S-(p-dialkyl-... 

Methyl iodide, reactions with dialkyl-amino-thiazoles, 32. See also Alkylation 4-Methylthiazole, preparation of, from Na/NH3 reduction of 4-methyl-A-4-thiazoline-2-thione, 397 2-Methylthio-3-methylthiazolium salts, as catalyst for methylthiothiazole rearrangement, 406 Methylvinylketone, reaction of, with... 

Condensation of thioamides with a-bromoketoesters under mild conditions gives 4-hydroxy-2-thiazolines which are easily dehydrated to afford thiazoles <86JHC577,86S992,88JHC289>. 2-Amino-4-arylsulfonylimino-2-thiazolines (320) can be prepared by reacting thiourea (or thiourea hydrochloride) with A-alkyl- or A, iV-dialkyl-iV -p-toluensulfonyl-a-chloroacetamidines (Equation (57)) <88JHC1849>. 

An extensive revision concerning the synthesis of thiazolo[3,2-n]benzimidazoles (400), thiazolo[3,4-fl]benzimidazoles (401), and thiazolo[3,2-c]benzimidazoles (402) has been reported <88H(27)1975>. All synthetic approaches to these systems involve the use of 2-thiobenzimidazole derivatives as starting materials the construction of the thiazole ring is carried out by intramolecular cyclization with a variety of reagents. The only exception is the preparation of compound (402) which is formed by the reaction of imidazo[5,l-6]thiazoles with dialkyl acetylendicarboxylate. 

Diary] and triaryl or naphthyl carbamates exhibit low herbicidal activity. The substitution of the aryl radical for a heterocyclic radical gives heterocyclic alkyl and dialkyl ureas, of which many examples have been prepared in recent years. The herbicidal activity of urea derivatives containing a heterocyclic radical, such as benzthiazole, thiazole, thiadiazole, oxadiazole and pyridine, is favourable if one or two methyl groups are substituted at the N -nitrogen. The carrier of total or selective action in these derivatives is presumably the heterocyclic part of the molecule. More recently several new groups of compounds have become known, mainly in the patent literature, for which the structure-activity on relationships are still to be elucidated. 

According to other synthesis methods, 3 can be prepared by coupling of the N - -dialkylated 2-(N-nitroimino)-hexahydro-l,3,5-triazine (21, R = alkyl, ary-lalkyl) with 2-chloro-5-(ffiloro-methyl)-l,3-thiazole (22, CCMT Table 29.2.1.9) at the 3-position and subsequent ring cleavage reaction of the resulting bis-aminal structure within the sbc-membered system of 23 (Scheme 29.2.1.3) [42, 43, 44]. 

Hantzsch s synthesis of A -thiazolines, like that of thiazoles (see this voL, p. 567), has been shown to involve isolable intermediate 4-hydroxy-hetero-cycles. A series of 3,4-dialkyl-A -thiazoline-2-thiones (162) were prepared from N-alkyldithiocarbamates and a-halogeno-ketones or -aldehydes in this work the stereochemical course of this reaction was elucidated (see... 

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