Azoles methylene compounds

Type G Syntheses (N-C-S-C-C). Various 2,4,5-trisubstituted thi-azoles have been prepared in good yield from thiocyanates R COCHR SCN (R2,R =H,alkyl,Ar,alkoxycarbonyl, acyl.benzoyl) and active methylene compounds CH-RR (R.R rCN, HCO,N00,alkanoyl,... 

There were only two reports ° of the displacement of hahdes in 1,3-azoles by carbanions of active methylene compounds before Yamanaka and co-workers detailed studies. Yamanaka s group investigated the reactivity of halo- or meth-anesulfonyl-substituted 1,3-azoles in aromatic Sisubstitution reactions and demonstrated the reactivity order of oxazole thiazole > iV-methylimidazole for displacement of methanesulfinate or halide at C(2) by carbanions of active methylene compounds (Scheme 1.176). For oxazoles, nucleophihc substitution follows the general order C(2) > C(5) > C(4). 

In analogous fashion, the basicity of the azole ring affects the ring closure to azolo-triazines 182 of the hydrazones 181 obtained from the coupling reaction of diazoazoles and methylene active compounds (76JMC517). 

The kinetics and product distributions of ozonolysis of vinylcyclohexane and methylene cyclohexane have been investigated.162 Steric hindrance of the cyclic substituent largely offsets electronic effects hi determining the rate of reaction. The main products of ozonation of catechols were quinones, while catechol acetals gave rise to compounds with an opened benzene ring.163 The ozonolysis of azoles such as pyrroles, oxazoles, and imidazoles has been reviewed.164... 

Formylpyrazoline-5-thiones undergo cyclo-condensation with compounds containing an active methyl or methylene group to give thieno[2,3-c]pyr azoles (74TL4069). The addition of 0.5 molar equivalent of dibenzoyl peroxide increases the yield from 29 to 77% (equation 59). 

The bisacylation of methylene-active compounds mentioned above can be avoided by using acylimidazoles in place of acyl halides (acylimidazoles are obtained from the carboxylic acid and sulfinyldiimidazole) for example, reaction of the magnesium enolate of ethyl hydrogen malonate and an acylimid-azole, with concomitant decarboxylation, gives the corresponding / -oxo ester 430... 

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