Thioureas formation

Thiomethyl iminoether formation, 289 Thiophene formation, cycloaddition, thioglycolate, 583 Thiophenodiazepine formation, 622 Thiophenol formation, 527 sulfonyl chloride, 527 Thiourea formation... 

Lysine, 4-amino Isocyanates, isothiocyanates Urea, thiourea formation... 

Scheme 12.31. Synthesis of decarbamoylsaxitoxin using a three-component thiourea formation/imine addition, by Hong and Kishi [110].

Like other heterocyclic iV-oxides, imidazole 3-oxides 1063 react with AC2O to give the corresponding imidazolones 1064 and 1065 (Scheme 257). TMSCN transforms 1063 into imidazole 2-carbonitriles 1066, whereas alkyl thiones convert 1063 to 1067 <2000HCA728, 1998HCA1585, 2002AGE2290>. The 2-aminoimidazoles 1068, formed from the reactions with either isocyanate or isothiocyanate, react further with isocyanates to form ureas but are inert toward thiourea formation. In contrast to nonaromatic imidazole A -oxides (nitrones), oxides 1063 react with DMAD to form butanedioates 1069, rather than the (putative) [3-1-2] adduct <2000T5405>. 

Thiourea formation Schiff s base formation Carbamate formation Alkylation... 

Lindahl, R., Levin, J. O., and Andersson, K., Determination of volatile amines in air by diffusive sampling, thiourea formation and high-performance hquid chromatography, J. Chromatogr., 643, 35-41, 1993. 

Figure 41. Projection diagram showing a hydrogen-bonded layer constructed from (thiourea-formate)2 tetramers in the crystal structure of (C2H5)4N HC02-(NH2)2 CS H2O (2.10). Broken lines represent hydrogen bonds.

It appears also that, for the synthesis of large libraries, there are few reactions that fulfil these prerequisites. Among the reactions that proved to have wide applicability, amide bond formations and peptide-like protecting group strategies can be found. In a general way all amine functionalization reactions are usually effective and lead to stable structures (i.e. sulfonamide, carbamate, urea, thiourea formation, reductive amination and nucleophilic substitution). Moreover, for any of these reactions the suitable linker can be easily selected from various literature sources. 

Another process makes use of the ability of some bacteria belonging to the genus Pseudomonas to convert DL-2-amino-thiazoline-4-carboxylic acid (DL-ATC) into L-cysteine." " DL-ATC is synthesized chemically from 2-chloroacrylic acid and thiourea. Formation of L-cysteine from DL-ATC is a three-step process catalyzed by different enzymes inside the cells 1) racemization of DL-ATC to L-ATC by ATC racemase, 2) formation of N-carbamoyl-L-cysteine (L-NCC) from L-ATC by L-ATC hydrolase and 3) hydrolysis of L-NCC to L-cysteine, NH3 and CO2 by L-NCC-amino-hydrolase. 

If unsupported reagents are used, only a trace of product is obtained, thus excluding a normal Hantzsch synthesis for 24 via thiourea formation. Instead, halogen displacement and cyclization of the a-isocyanatoketones 25 via 26/27 seems to be reasonable. 

The heat stability of N,N -dipentamethylenethiuram disulphide was studied and compared with that of TMTD with respect to thiourea formation. The agent responsible for degradation was investigated and identified as alkyldithiocarbamic acid, which, upon decomposition, produced amine. The effectiveness of zinc compounds, such as ZnO and zinc bis(pentamethylenedithio-carbamate), in preventing degradation was also examined. 22 refs. 

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