Aryl cyanates

Aminothiatriazole (328) reacts with a number of aryl cyanates at 0°C to afford 3-substituted 5-amino-l,2,4-thiadiazoles (17) in moderate yields. 5-Aminothiatriazole (328) also reacts with trichloroacetonitrile to give (17) (R = CCI3) in 92% yield. When these reactions are carried out at 30 °C, the thiadiazoles (17) react with a second mole of aryl cyanate to give the amidino compounds (329) (Scheme 72) <85JOCl295>. 

Martin et al. reacted alkyl and aryl cyanates with 5-aminothiatriazoles (13) at 0°C in aprotic solvents <85J0C1295>. The reaction led to evolution of nitrogen and the formation of 3-substituted-5-amino-l,2,4-thiadiazoles (117) in 40-65% yield. If the reaction was carried out at 30°C or if two equivalents of cyanate was employed a subsequent reaction to the corresponding amidino compound (118) took place (Scheme 22). 

The reaction of Ph 3P=CH2 with benzoyl isocyanate takes place in a 1 2 ratio with loss of benzene to afford the ylide 173 <71JOC2029> and treatment of either Ph3P=CHC02Me or Ph3P=CHC02Et with aryl cyanates, Ar-O-CN, results in formation of the pyrimidine ylides 174 <67CB187>. An alternative means of access to 171 (R = cyclohexyl) is provided by... 

For reviews of alkyl and aryl cyanates, see Jensen Holm in Patai The Chemistry of Cyanates and Their Thio Derivatives, pt. 1 Wiley New York, 1977, pp. 569-618 Grigat Putter Angew. Chem. Int. Ed. Engl. 1967, 6. 206-2 8 [Angew. Chem. 79, 219-231],... 

Benzoyl chloride condenses with benzonitrile or aryl cyanates in the presence of aluminum trichloride to give 1,3,5-oxadiazinium salts (Scheme 58) (67CB3736). 

Aryl cyanates react with ammonia to form the bis(iminoethers) (100). These compounds form 1,3,5-triazines by reaction with a further equivalent of the cyanate (Scheme 58) (67AG(E)206). IV-Amidoamidines condense with ethyl oxalate to form 2-amino-1,3,5-triazines (equation 53) (71CPB1789). 

Aryl cyanates react with cyanamides to form (114), which reacts with a further equivalent of aryl cyanate to form the 2,4-bis(aryloxy)-l,3,5-triazine (115) in strongly alkaline conditions (Scheme 64) <67AG(E)206>. 

Aryl cyanates (cyanic esters), which can be prepared in situ (67AG(E)206), form 1,3,5-triazines under either acid or base catalysis (Scheme 83) (77RCR278, 78RCR975). The acid-catalyzed reactions are not properly understood, but it seems that the mechanism is dependent on the precise nature of the Lewis acid used. Yields are usually good (Table 14). The reaction of aryl cyanates with ketoximines yields 1,3,5-triazines (146) via the intermediate (145) (Scheme 84) (66CB2361). Alkyl cyanates are very reactive, and isomerize readily therefore they are unsuitable starting materials for 1,3,5-triazine synthesis. 

An analogous product (252 X = Cl) is formed in the reaction of sulfur trioxide with cyanogen chloride (68AG(E)172). Aryl cyanates also condense with sulfur trioxide to give 1,2,3,5-oxathiadiazines analogous to those formed from dialkylcyanamides (67CB3736). 

The first synthesis of ethyl cyanate48 from 5-ethoxythiatriazole49 was briefly mentioned in the previous review of thiatriazoles.1 The thiatriazole decomposes smoothly in ethereal solution at 20° with formation of nitrogen, sulfur, and ethyl cyanate. Although several other methods are now available for the preparation of both alkyl and aryl cyanates the thiatriazole method prevails as the most generally applicable for the thermally and chemically sensitive alkyl cyanates, since the only by-products are inert—sulfur and nitrogen. Thus a number of 5-alkoxy,50-54 5-aryloxy,55-57 and 5-aralkoxythiatriazoles12,53 have been prepared. 

Similarly, the aryl cyanates 2b-d were quantitatively obtained. 

Scheme 19 Palladium-catalyzed aryl cyanation using a triaryl phosphine on polymer-support...

The condensation of ketene-S,S-hemiacetal 29 with aryl cyanates leads to 2-aryloxy-TA 30 (85ZC430) (Scheme 5). 

Aryl cyanates serve the same purpose in reactions with 11, which lead to 38. ... 

Arenediazo cyanides, 127 Arenediazonium tetrafluoroborates, 127 Arenesulfonylhydrazones, 243-244 Aristolene, 440 Aromatization, 389 Ar-turmerone, 313, 521 Arylacetylenes, 309 Aryl cyanation, 423 /3-Arylcyclopcntanones, 124 Aryl diazonium salts, 465... 

Aryl cyanation. Reaction of iodobenzene with sodium cyanide in the presence of 10 mole % of Pd(0) affords only a 5% yield of benzonitrile. If the sodium cyanide is impregnated on alumina the reaction proceeds in quantitative yield. In the same reaction with aryl bromides higher yields obtain when alumina is present as a co-catalyst rather than as a support. 

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