Aryl isocyanates insertion reactions

A (pentamethylcyclopentadienyl)iridium chelating guanidinate complex has been conveniently prepared by treatment of [Cp IrCl2]2 with N,N, N"-th-p-tolylguanidine and base in THF at room temperature followed by recrystallization of the green product from toluene and pentane (Scheme 154). Insertion reactions of the product with heterocumulenes (diaryl carbodiimides, aryl isocyanates) have been investigated. It was found that the complex serves as highly active catalyst for the metathesis of diaryl carbodiimides with each other and for the more difficult metathesis of diaryl carbodiimides with aryl isocyanates (cf. Section V.C). ... 

Insertion reactions involving metal alkoxides are also known. For example, carbon dioxide is known to react with some metal alkoxides as shown in equation (12). The formation of a bidentate ligand is a significant thermodynamic driving force for some of these reactions. The isoelectronic aryl and alkyl isocyanates and carbodiimides can react similarly. Insertion reactions involving alkenes and carbon monoxide are known for platinum alkoxides. 

Multi]de insertion reactions of isocyanates have been observed in the presence of Ni catalysts. Pyri-midinediones are obtained in low yield from reaction of diphenylacetylene with excess alkyl isocyanates in the presence of Ni(COD). Similarly, alkyl and aryl isocyanates undergo simple cyclotrimerization to form symmetrical triazinetriones in the presence of both low-valent Ni and Ti catalysts. 

Acetylenes yield acrylanilides by insertion of aryl isocyanate into an intermediate tantalum complex, as shown in reaction 9. ... 

As with the aryl compounds the reaction scheme is simplified for the sake of clarity. The reactions observed are various and include reductive coupling (ketones, nitriles), insertion (diphenylacetylene, isocyanate, isonitrile, CO2 and CO), and disproportionation (diphenylacetylene, CS2). The course of the reactions and the complexity of the product mixtures strongly depend on the nature of the alkyl groups and the substituents on the substrate molecule. As examples we will discuss reactions with ketones, acetylenes and CO. The reaction with ketones strongly resembles the coupling of nitriles R C=N on Cp2TiR (R = aryl). The coupling proceeds more slowly when R, R and R" increase in size. 

Some homologous monomeric iridium imido complexes have been described by Bergman et al. and their insertion reactions with CO to afford aryl or alkyl isocyanates reported [105]. However, even these eomplexes are not part of any catalytic cycle and will not be discussed. 

One-Atom Insertions. Siliranes also undergo one-atom insertion reactions with elemental sulfur, oxygen, or selenium. Similarly, the insertion of aryl or alkyl isocyanates provides iminosi-lacyclobutanes in high yield as single stereoisomers (eq 7). The reaction proceeds with the retention of silacyclopropane configuration and the insertion occurs at the more substituted C-Si bond when unsymmetrical siliranes are employed, similar to the regios-electivity observed for aldehydes and formamides. 

Numerous CH insertion reactions of isocyanates involve substrates with a CH2CO group. For example, dialkyl malonates, malonitrile , ethyl cyanoacetate and oxaloacetic esters react with alkyl and aryl isocyanates at room temperature, in the presence of triethylamine, to give products resulting from insertion into the activated C-H bond as... 

In the reaction of ketoglutaric acid esters with aryl isocyanates ring closure of the initiallly formed insertion products 231 occurs to produce the heterocycle 232 . ... 

Insertion into O-C-0, N-C-N and C-halogen bonds is also observed. Orthoformates also form 1 1 adducts with alkyl or aryl isocyanates if the reaction is conducted at 30-70 °C in the presence of a Lewis acid catalyst. An insertion reaction of isocyanate into oxetane 245, in the presence of Bu2Snl2 and PhsR to give the cyclic carbamate 246 is also observed. ... 

Organoaluminum compounds also undergo insertion reaction with isocyanates. For example, aluminum trialkyls react with alkyl and aryl isocyanates to give carboxylic acid amides after hydrolysis . Alkyl aluminum chlorides react similarly . Aluminium trichloride also forms insertion products with isocyanates Diethylaluminum ethyl thiolate or dimethylamide react with equimolar amounts of alkyl or aryl isocyanates to give the expected insertion products 274. ... 

Tin (iv) alkoxides and oxides react similarly with alkyl and aryl isocyanates . On treating bis-tributyl tin oxide with two different isocyanates, isocyanurates 277 are obtained via repeated insertion reactions... 

Metalorganic substrates derived from niobium and tantalum also undergo insertion reactions into metal-carbon and metal-hydrogen bonds. Also, stepwise insertion into Nb(OR)5 is observed . Similarly, chromium trialkoxides undergo insertion reactions with aryl isocyanates ". ... 

Nickel alkoxides undergo reactions with aryl isocyanates to give the expected mono- 332 and di-insertion products 333 . ... 

Thermolysis of the thiadiazole (164) leads to elimination of isocyanate and sulfur giving the triazine derivative (167). If the thermolysis is carried out in the presence of phenols 2-aryl-benzimidazoles (168) are produced <85JCS(P1)1007>. The S—N bond of (157) is readily cleaved with both N- and C-nucleophiles. Thus, treatment of (157) with an excess of amine gives the sulfenamide (169) (Scheme 39) and reaction of (157) with active methylene compounds leads to derivatives of type (170) (Scheme 39) which on heating furnish (171). Cyanide ion inserts into the S—N bond of (164), probably via the intermediate (172) which immediately recyclizes to give the thiadiazinone (173) (Scheme 40) <85JCS(P1)1007>. 

H)-Oxazolones are formed by the spontaneous cyclization of /3-oxo isocyanates (equation 134). Similarly, o-hydroxyphenyl isocyanate, produced by the Curtius rearrangement of the azide of salicylic acid or by the action of sodium hypochlorite on salicylamide, forms benzoxazolone (equation 135). An analogous reaction is the formation of IV-phenyl-benzoxazolone by the action of thionyl chloride on the hydroxamic acid shown in equation (136) (78TL2325). Pyrolysis of aryl azidoformates affords benzoxazolones by nitrene insertion (equation 137) (81CC241). 

Many examples of alkene and alkyne insertion into metal-carbon bonds can also be found in the section on homogeneous catalysis. Other recent examples include the insertion of conjugated dienes into palladium-allyl bonds, olefin arylation in the presence of palladium acetate, and the reaction of ethylene with arylmagnesium halides in the presence of nickel chloride. Reaction of isocyanates with nickel-ethynyl compounds... 

Two equivalents of the isocyanate react with cyanotrimethylsilane at 50 °C to give a flve-membered ring [2+2+1] cycloadduct. Af,Af -disubstituted 5-trimethyl-silyliminoimidazolidinediones are obtained in the reaction of aryl- or arenesulfonyl isocyanates with trimethylsilyl cyanide. In the reaction with arenesulfonyl isocyanates the initially formed insertion products can also be isolated. The reaction of trimethylsilylamldes with phenylcarbonyl isocyanate also affords the insertion product. 

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