Aryl cyanates, reactions with

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 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. 

Aryl cyanates react with aromatic acid chlorides in the presence of anlimony(V) chloride to give 2-aryl-4,6-bis(aryloxy)oxadiazinium salts 5a, b 62 thiocyanates react analogously giving 5c-n but in this case the reaction is of wider scope as both the thiocyanates and the acid chlorides may be aromatic or aliphatic.63,64... 

When at least 2 equivalents of an aryl cyanate 9 are treated with one equivalent of ammonia in anhydrous ethereal solution, iminobiscarboximidates 10 can be isolated361,362 (cf. Houben-Weyl, Vol. E4, p 1073). Compounds 10 can be converted to 1,3,5-triazines by reaction with either a further equivalent of aryl cyanate, or with formylating reagents such as triethyl orthoformate.362 A direct synthesis of 1,3,5-triazines 11 from aryl cyanates and ammonium carbonate in aqueous solution has also been described.363... 

The mechanism of action of the cyanation reaction is considered to progress as follows an oxidative addition reaction occurs between the aryl halide and a palladium(O) species to form an arylpalladium halide complex which then undergoes a ligand exchange reaction with CuCN thus transforming to an arylpalladium cyanide. Reductive elimination of the arylpalladium cyanide then gives the aryl cyanide. 

Long-lived homogeneous Pd(0)f4 [L = P(Ph)3] catalysts for the cyanation of aryl chlorides (295) (X = Cl) have been developed, which are activated by cathodic reduction (Scheme 113) [433]. A high temperature, 130 °C, and a high-boihng solvent, dimethylformamide, are required because Pd does not insert into the aryl C—Cl bond at lower temperatures. Cat-alytically inactive metal species formed in undesirable side reactions with cyanide are electrochemically restored to a catalytically... 

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... 

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 nickel-catalyzed transformation of aromatic halides into the corresponding nitriles by reaction with cyanide ions is reported. Both tris(triarylphosphine)nickel(0) complexes and tY2ins-chloro( aryl )bis( triarylphosphine )nickel(II) complexes catalyze the reaction. The influence of solvents, organophos-phines, and substituents on the aromatic nucleus on catalytic cyanation is studied. A mechanism of the catalytic process is suggested based on the study of stoichiometric cyanation of ti3ins-chloro(aryl)bis(triphenylphosphine)nickel-(II) complexes with NaCN and the oxidative addition reaction of Ni[P(C6H5)3]s with substituted aryl halides. 

Therefore it seems reasonable to assume that cyanation of aryl halides involves two fundamental processes oxidative addition of the tris(triphenylphosphine)nickel complex on the aromatic halide (Reaction 2) and cyanation of the arylnickel(II) complex 1 (Reaction 8). A further proof of the validity of this scheme is that both Ni[P(C6H5)3]3 and arylnickel (II) complexes 1 have an equal catalytic activity, these latter being intermediates of the catalytic process. Recent studies (22) on the influence of substituents on the aromatic halide in the oxidative addition reaction with Ni[P(C6H5)3]3 have given the results shown in Figure 4. 

Me3SiCN is a convenient, reactive cyanide donor in transition metal-catalyzed processes. The Pd-catalyzed reaction of aryl iodides with Me3SiCN is useful for the synthesis of aryl cyanides.257 Me3SiCN works also as an effective co-catalyst for the Pd-catalyzed cyanation of aryl iodides with KCN.258 Allylic acetates, carbonates, and the related compounds undergo the Pd-catalyzed cyanation with Me3SiCN.259-261 The tandem cyclization-cyanation reaction of 2-bromo-l,6-heptadienes with Me3SiCN proceeds under catalysis by an Ni complex (Equation (68)).262... 

The palladium-catalyzed reaction of aryl halides with cyanides to give cyanobenzenes takes place under relatively mild conditions compared to the conventional method using a stoichiometric amount of CuCN [74]. Thus, palladium catalysis has been often employed. Recently, a number of effective methods for the cyanation have been reported. The reaction of aryl iodides with NaCN under two-phase conditions [75] and those of aryl triflates [76, 77] and aryl chlorides [78] with Zn(CN)2 occur with good efficiency, while these are considered to proceed via mechanism B. 

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

Aryl cyanates can be prepared by reaction of phenols with cyanogen halides in the presence of a base ArO + CICN ArOCN + CP. This reaction has also been applied to certain alkyl cyanates. ... 

An indirect method involves the reaction of an aromatic ring with tert-butyl-lithium, particularly when there is a directing group (see 13-17), followed by reaction with PhOCN (phenyl cyanate) to give the aryl nitrile. another indirect method involve the palladium catalyzed reaction of aryl bromides with the cyanohydrin of acetone [Me2C(OH)CN] to give ArCN. ... 

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