Heterocyclic synthesis thioureas

The present volume encompasses a wide range of heterocyclic chemistry. Syntheses of heterocycles from thioureas are reviewed by T. S. Criffin, T. S. Woods, and 1). L. Klayman, while S. W. Schneller describes the chemistry of benzothiins and their derivatives (thiochromans, thiochromones, and thio-chromanones). Developments in chrom-3-ene chemistry are reviewed by L. Merlini. F. D. Popp contributes a chapter on the isatins. A discussion of theoretical aspects of the tautomerism of pyrimidines, by J. S. Kwiatkowski and B. Pullman, follows up a corresponding earlier contribution (Vol. 13) on tautomeric purines. In the final chapter P. and D. Cagniant describe the natural occurrence and synthesis of the benzofurans. 

The heterocyclic-oriented thioureas have scarcely been reported in the research field of drug-like library construction by solid-phase synthesis, compared to their ureas and simple aromatic thiourea analogues. We have previously described the dithiocarbazate linker 42 and its application to drug-like heterocycle formation." The key intermediate, the... 

Analogous Benzotriazole-mediated syntheses are available, for example, for diaryl-methanes, dieneamines, and N,N-disubstituted thioureas (Katritzky methodology, 1990 for applications in heterocyclic synthesis, cf Ref [510]). 

In a similar way, 1,3-dinitrogen systems such as diamines, amidines, guanidines, aminothiazoles, aminopyridines, ureas and thioureas react with alkynyl-carbene complexes generating the corresponding heterocycles. Of particular interest is the reaction with ureas, as the process can be applied to the easy synthesis of pyrimidine derivatives [88] (Scheme 41). 

There is an enormous literature on thiocarbonyl compounds, due in part to the technical and industrial importance of many of them, including thioamides, thioureas, xanthates, dithiocarbamates and so forth. An excellent, and recent, general review is available.107 There are also specialized reviews germane to the present chapter Griffin, Woods, and Klayman2 discussed the use of thioureas in the synthesis of heterocycles the preparation of thiazoles from thioamides is included in a three-part volume on Thiazoles 108 the use of carbon disulfide in the synthesis of trithiones and related heterocycles has been reviewed by Mayer109 and Huisgen110 has reported numerous examples of 1,3-dipolar cycloadditions in which carbon disulfide was used. 

Alternative precursors for the synthesis of NHCs are thiourea derivatives of type 3. The preparation of such thiones with a symmetrical substitution pattern is achieved by the reaction of a-hydroxyketones like 3-hydroxy-2-butanone with suitable 2-thiones (Fig. 3d) [31] or by reaction of a diamine with thiophosgene [32, 33]. Unsymmetrically substituted thiones 4 possessing a saturated heterocycle have also been described (Fig. 3e) [34, 35]. 

The Molecules R2CXCR2 Including Azomethine, Carbonyl and Thiocarbonyl Ylides Their Syntheses, Properties and Reactions R. M. Kellogg, Tetrahedron, 1976,32,2165-2184. Thioureas in the Synthesis of Heterocycles T. S. Griffin, T. S. Woods and D. L. Klayman, Adv. Heterocycl. Chem., 1975,18, 100-158. 

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