Alkyl isocyanates insertion reactions

Alkyl isocyanates insert into tungsten and iron hydride complexes to give the insertion products resulting from insertion into the metal-hydrogen bond. For example, reaction of CpW(CO)3H with methyl isocyanate affords the carbamate complex . Likewise, CpFe(CO)2H reacts with t-butyl isocyanate to give the carbamate complex 329 . 

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. 

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... 

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. ... 

The insertion reaction of isocyanates into C-Cl bonds requires Lewis acids or carbon as a catalyst. For example, alkyl isocyanates react with phosgene at 150 °C, in the presence of carbon, to give the insertion product 256. A better synthesis of the insertion product is the reaction of the sulfur heterocycle 257 with chlorine... 

The insertion reaction of isocyanates into numerous metalorganic compounds is well documented. For example, reactions of t-BuLi, s-BuLi and n-BuLi with carbon monoxide in the presence of alkyl isocyanates afford a-oxoamides 262. ... 

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... 

N-benzylaniline with phosgene, and then with sodium azide to produce carbonyl azide 52. On heating, nitrogen is evolved and a separable mixture of nitrene insertion product 53 and the desired ketoindazole 54 results. The latter reaction appears to be a Curtius-type rearrangement to produce an N-isocyanate (54a), which then cyclizes. Alkylation of the enol of 54... 

Another common process involves reaction with C=C or C=N species having adjacent CH2 or CH, groups. Initial attack of the isocyanate is on the electron-rich center of the double bond with subsequent migration and insertion of the CONR group into the CH bond. Suitable reagents include N-alkylated acetamidines, 1-methyl dihydroisoquinoline, and 2-methyl-2-oxazoline [1120-64-5] (35). 

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. 

---