Isocyanates insertion reactions

Organocopper compounds react slowly with nitriles or not at all 124, 233). Only a low yield of benzanilide was obtained from the reaction between phenylcopper and phenyl isocyanate 124). Isocyanate insertion reactions with vinylcopper compounds in HMPT in the presence of P(0C2H5)3 afford acrylamides 225a). 

Insertion Reactions. Isocyanates also may undergo iasertion reactions with C—H bonds. Acidic compounds, such as 1,3-dicarbonyl compounds (6), react readily at room temperature to form carboxyamides. At higher temperatures carboxyamides frequentiy undergo secondary reactions leading to cyclized products (33,34). 

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). ... 

Chromatography cyclophosphazenes, 21 46, 59 technetium, 11 48-49 Chromites, as spinel structures, 2 30 Chromium, see Tetranuclear d-block metal complexes, chromium acetylene complexes of, 4 104 alkoxides, 26 276-283 bimetallics, 26 328 dimeric cyclopentdienyl, 26 282-283 divalent complexes, 26 282 nitrosyls, 26 280-281 trivalent complexes, 26 276-280 adamantoxides, 26 320 di(/ >rt-butyl)methoxides, 26 321-325 electronic spectra, 26 277-279 isocyanate insertion, 26 280 substitution reactions, 26 278-279 [9]aneS, complexes, 35 11 atom... 

Figure G shows some insertion reactions of carbonyl compounds. In the isocyanate and ketene cases, the addition takes place, not to the carbonyl double bond, but to the carbon—nitrogen or the carbon—carbon double bond.

Recently an arsenic amide derivative has reacted with an isocyanate, adding across the carbon—nitrogen double bond. I think this is the first example of a group V element which seems to be undergoing an insertion reaction. 

Zirconium and hafnium dialkylamides are highly reactive compounds. They undergo (i) protolytic substitution reactions with reagents such as alcohols, cyclopentadiene and bisftrimethylsilyOamine 63 64 (ii) insertion reactions with C02, CS2, COS, nitriles, phenyl isocyanate, methyl isothiocyanate, carbodiimides and dimethyl acetylenedicarboxylate 69-72 and (iii) addition reactions with metal carbonyls.73 These reactions are summarized with reference to Zr(NMe2)4 in Scheme 1. 

Alkoxides of nickel(II) are conveniently prepared according to equation (177) in anhydrous conditions.1487 1488 All of these compounds are insoluble in the common organic solvents. Complexes with primary alkoxides are green and six-coordinated complexes with secondary and tertiary alkoxides are tetrahedral with colours ranging from blue to violet. All of the complexes decompose at about 90-100°C. The complexes with secondary and tertiary alkoxides undergo alcoholysis reactions when dissolved in primary alcohols. An interesting insertion reaction occurs when nickel alkoxide reacts with some isocyanates (equation 178).1489... 

Insertion Reactions. Isocyanates also may undergo insertion reactions with C—H bonds. 

A variety of olefins or aromatic compounds having electron-donating substituents are known to undergo C—H insertion reactions with isocyanates to form amides (36,37). Many of these reactions are known to involve cyclic intermediates. 

Isocyanates insert into RO and RN bonds. Cyclic ethers, such as oxiranes, are known to undergo reactions with isocyanates to form 2-oxazolidinones in high yield (38—40). 

A new series of niobium derivatives (62) of the IV-phenylurethanes has been obtained586 from the insertion reaction between niobium penta-alkoxides and phenyl isocyanate. Most of the products are yellow liquids, one is white and the rest are brown or black solids or semi-solids. They exhibit v(C=0) in the range 1690— 1730 cm-1. Insertion of up to three molecules of phenyl isocyanate occurs readily at... 

Accordingly, cycloaddition reactions can be carried out in solvents such as alkanes, cycloalkanes and acetonitrile. The insertion reaction into the O-H-bond of alcohols is, in every case, faster than the cycloaddition reaction. Furthermore, 100% production of isocyanate was observed upon irradiation of benzoyl azide in dichloromethane solution, however, nitrenes that can be trapped by compounds with double bonds are also formed in this solvent [21]. 

The reaction can be run in reverse at high [THF], with bis-(trimethylsilyl) carbodiimide replaced by THF. The rate is independent of [THF], consistent with rate-limiting extrusion of carbodiimide, i.e., with the operation of a similar dissociative mechanism in reverse. Similarly, addition of trimethylphos-phine to 35 results in extrusion of the carbodiimide to form the phosphine-stabilized zirconaaziridine [49]. In contrast, the isocyanate insertions are effectively irreversible. 

Isocyanate insertions presumably go through the same 16-electron intermediate, which explains why the Zr-N/Zr-C ratio from those reactions is inde-... 

Insertion reactions can proceed with isocyanides, isocyanates, organic azides, and so on,155 e.g.,... 

The insertion reaction of heterocumulenes can be used to syuthesize carbodiimides having two different substituents. For example, the carbamate 157 derived from an isocyanate and bis(tributyltin)oxide can be reacted with an isothiocyanate to give a carbodiimide 158 with substituents derived from the isocyanate and the isothiocyanate. ... 

Heterocumulenes undergo insertion reactions with numerous substrates. In general, carbodiimides react faster than isocyanates and isothiocyanates, in that order. Insertions of carbodiimides into metal-hydrogen, metal-halogen, metal-mitrogen, metal-oxygen and metal-sulfur bonds are reported. Also insertions of carbodiimides into carbon-hydrogen bonds are known. 

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. 

The azabicyclononane system is a common structural feature in diterpene alkaloids, and the nitrene insertion route to the ring system has been studied in detail in model decalins as well as in steroids (Scheme 11). Thus irradiation of the rrans-acyl azide (21) gave, in addition to isocyanate (30-33%), a mixture of Ae 7- and 8-lactams (22) and (23). The y-lactam (22) predominated, dthough the overall yield was poor. > The corresponding c/s-azide (24), however, gave the 8-lactam (25) as Ae major product, again in low yield. One elegant application of this type of intramolecular nitrene insertion reaction... 

Insertion reactions of heterocycles with isocyanates 87ZC77. Investigation of reactions of heterocycles by the use of radioactive sulfur 88MI18 90MI14. 

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. 

CO2 analogues such as allenes, ketenes, isocyanates, carbodiimides, and carbonyl sulfide also insert. Studies of insertion reactions of Cp2ZrR2 (R = Me, CH2Ph, Ph) show that the ease of insertion follows the series Me > Py CH2Ph and Ph2C=C=0>PhN=C=0>p-MeC6H4N=C=NC6H4Me-p>C02. The data have been reasonably interpreted as evidence for precoordination before insertion occurs. A four-center transition state similar to that depicted above for the thorium system is favored. 

Insertion Reactions of an Isocyanate, Isothiocyanate, Carbodiimide, Ketene, Diketene, or Ketenimine... 

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