Isocyanates, RNCO

Note that carbon monoxide inserts into the Zr-H bond of 1 (2 equiv.) to afford an T -formaldehydo-type complex [(Cp2ZrCl)]2(g-CH20) [200-202]. Iminoacyl zir-conocene complexes are formed after addition of 1 to isonitriles [203]. Carbon dioxide [183, 202] is reduced to formaldehyde with 1 (2 equiv.). C02-like molecules such as isocyanates RNCO [204], isothiocyanates RNCS [205], and carbodiimides RNCNR [204] are readily converted to the corresponding bidentate form-amido ligands. 

Scheme IV.64). The same rearrangement was reported for the reaction with isocyanates (RNCO) and isothiocyanates (RCNS) (96HAC97). 

The indeno fused compounds (521) have been prepared in moderate yield by the photochemical reaction of 2,5-diaryl-l,3,4-oxadiazoles (519) with indene (77JOC1496) the reaction is thought to proceed via a diradical or betaine (520). These products react with isocyanates (RNCO) to give the triazepine system, e.g. (522) (76H(4)989). 

Thermolysis of pyridine A-acylimides (981) gives isocyanates RNCO and pyridine. Photochemical rearrangements of A-imides can be complex (Scheme 76). 

Trimerization of imidates is a valuable route to 1,3,5-triazines. Imidates can be considered as activated nitriles and cyclotrimerize more readily. Most symmetrical 2,4,6-trialkyl-1,3,5-triazines are easily formed, although large alkyl substituents may give rise to steric hindrance (61JOC2778). Symmetrical isocyanurates (525) are readily available from isocyanates, RNCO catalysts include tertiary amines, phosphines and sodium methoxide. Aldehydes RCHO and ammonia give hexahydro-1,3,5-triazines (526), known as aldehyde ammonias (73JOC3288). 

Table 16 Synthesis of Symmetrical Isocyanurates from Isocyanates (RNCO)...

Hydroxy-n-propylhydrazine (3-hydrazylpropanol) was cyclized with ethyl carbonate to yield 17 (R = NH2). The reaction was followed by treatment with isocyanate, RNCO, to form a urea derivative 19.85... 

The reaction of 4,5-dihydro-4//-l,2,4-thiadiazine 1,1-dioxides 142, which have a leavable group in the 3-position (Y = OR1, SR1, NH2), with two molecules of an alkyl isocyanate (RNCO) produces the condensed system 143, while the alkyl isothiocyanate yields the different condensed system 145. The former reaction apparently proceeds through intermediate 144, i.e., by reaction at the 4-position. On the other hand, the first molecule of the isothiocyanate may, by analogy, react at the 2-position via a corresponding intermediate (74BSF1917). 

The oxidation of phenylhydrazine and 1,2-disubstituted hydrazines to hydrazones and diazenes by CI2C proceeds via formation of unstable azomethine imines.95 The conversion of alcohols into alkyl halides is achieved by reaction with CCI4 (or CBr4) in DMF under electrochemical reduction.96 The reaction of dihalocarbene X2C with DMF to form a Vilsmaier reagent (93) is proposed as the key process. The reaction of simple isocyanates (RNCO) with dimethoxycarbene normally gives hydantoin-type products. In the reaction with vinyhsocyanates such as (94), however, hydroindoles (95) are formed in good yields.97... 

The reaction of metal N-alkylcarbamates M(C)2CN 11 R) (M = Na, Mn(II), Co(II) R = Ph, Pr, Cy) with R C(0)C1 (R = Me, Ph) takes place, at ambient temperature, in a more complex way with the formation of isocyanates (RNCO), carboxylic anhydrides (R C(0)0C(0)CR ), amides (RNHC(O)R ) and C02. Amide formation and the evolution of C02 can be due to (i) the decomposition of mixed anhydride RNHC(0)0C(0)R obtained by addition of the acyl chloride to the oxygen atom of the carbamate group or (ii) the direct reaction of acyl chloride at the carbamic nitrogen atom of M(02CNHR) . The mixed anhydride RNHC(O) 0C(0)R might also decompose via another route so as to afford isocyanate and carboxylic acid. However, a different pathway (Scheme 6.6) has been also envisaged for the formation of RNCO and R C(0)0C(0)CR, which excludes any intermediacy of the mixed anhydride [61a], Two acetic acid molecules, bound to the same metal or to different metal centers, would then be dehydrated and acetic... 

Isocyanates (RNCO) are industrially relevant compounds which find application in several fields [9, 106]. Many isocyanates serve as the starting materials for the manufacture of plant protection agents, pesticides, dyes, resins and plastics, textile waterproofing agents, detergents, bleaches, and adhesives. They are also widely used in surface coatings such as paints, sealants and finishes, and in the manufacture of rubbery plastics such as those used to coat wires. Traditionally, diisocyanates are the primary feedstock for the production of polyurethanes. The global market for diisocyanates in the year 2000 was 4.4 million tonnes, of which 61.3% was methylene diphenyl diisocyanate (MDI), 34.1% was toluene diisocyanate... 

The use of the toxic and hazardous hydrazoic acid is avoided by generating it in situ by adding sodium azide gradually to the carboxylic acid in the presence of concentrated sulphuric acid and chloroform (eg.. 3,5-dinitroaniline, Expt 6.54). The reaction involves the hydrolysis of an intermediate isocyanate (RNCO), which is formed by a mechanistic pathway analogous to that involved in the Hofmann reaction. 

The simplest neutral N,0-donor ligand systems are the alkyl(aryl)isocyanates RNCO. As reported [112], little attention is dedicated to these ligands, despite their... 

Isocyanates have provided one carbon atom in transformations of the general type (296) - (290). Thus, azide (343) reacts with triphenylphosphine in a Staudinger reaction giving phosphorane (344) which is then treated with isocyanates (RNCO R = benzyl or aryl) giving naphthyridines (346) (50-59% yield) via the carbodiimide (345). The cyclization (345)->(346) occurred in toluene at 160°C (92T4601). Azide (347) undergoes a similar sequence of reactions yielding a 1 1 mixture of isomeric naphthyridines (348) and (349) (44—47% yield). 

The cycloaddition of isomiinchnones with acetylenic dipolarophiles followed by the extrusion of an alkyl or aryl isocyanate (RNCO) has proven to be an effective method for the synthesis of substituted furans. The Ibata group investigated the bimolecular 1,3-dipolar-cycloaddition of aryl-substituted isomiinchnones with a number of acetylenic dipolarophiles [50]. Aryl diazoimides of type 1 were heated in the presence of a catalytic amount of Cu(acac)2 and the appropriate acetylenic dipolarophile. Formation of the substituted furan was found to be temperature-dependent higher temperatures (ca. 120°C) were needed for complete conversion to the furan. It was reasoned that the extrusion of methyl isocyanate was not as facile as the loss of carbon dioxide from sydnones and miinchnones [50]. 

The insertion of isocyanates, isolelectronic with C02, proceeded more cleanly. Isocyanates (RNCO) with bulky R groups inserted exclusively into the Zr-C bond (Table 5) methanolysis resulted in a-amino amides 32 [21]. 

Organic Isocyanates, RNCO. These are normally bound rf-N, C.213... 

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