Subject reaction with isocyanates

The 1,3,2-dioxastannolanes are important in organic synthesis because they can readily be derived from dialkyltin oxide and 1,2-diols, as in carbohydrates the reaction can be carried out in toluene in a few minutes under microwave irradiation.387 The dioxastannolanes can then be subjected to regioselective reaction with an electrophile such as an acyl chloride (Equation (140)) or sulfonyl chloride, or an isocyanate. The acylation or sulfonation can be carried out with catalytic amounts of the dialkyltin oxide, including the recoverable (C6F13CH2CH2)2Sn0.388... 

Isocyanates react readily with water to form amines and polyureas (Chadwick and Cleveland 1981 Hulse 1984 Kennedy and Brown 1992) and hydrolysis of HDI is expected to occur much more rapidly than biodegradation (HSDB 1995). Consequently, reaction with water is expected to be the only significant fate proeess of HDI in moist soil or sediment. The HDA resulting from hydrolysis, however, should be subject to various types of biodegradation (HSDB 1995). Gilbert (1988) has summarized the results of laboratory experiments on TDI in undistiubed moist sand, which indicate that TDI is converted to polyureas at a rapidly decreasing rate, with 5.5 and 3.5% of unreacted TDI remaining after 24 hours and 8 days, respeetively. The toluene diamine hydrolysis produet was not found above the detection limit of 0.01 ppm. These results were... 

Scheme 16 shows parallel syntheses of cyclic and acyclic amide compounds. Fluorous benzaldehydes were first subjected to reductive amination reactions. The resulting amines were then reacted with isocyanates to form substituted hydantoin rings 14 or with benzoyl chlorides to form amides 15. Purified F-sulfonates were used for palladium-catalyzed cross-coupling reactions to form corresponding biaryl 16 [31] and arylsulfide 17 [32] products, respectively. 

Nitrogen-based heterocycles can also be prepared through Ni/NHC-catalyzed cyclo addition reactions. For example, Ni/SIPr catalyzed the cycloaddition of diynes with isocyanates under the mildest conditions to date [26]. In particular, excellent yields of pyridones are obtained from diynes and isocyanates at room temperature using only 3 mol % catalyst. As shown in Eq. 8, a variety of diynes were subjected to these optimized conditions. Both aryl and alkyl isocyanates were readily converted to the respective 2-pyridone. Sterically hindered substrates appeared to have very little effect on the reaction, as excellent yields of product were obtained with bulky isocyanates and bulky diynes. 

An extensive review of the reactions of isocyanates with hydroxy compounds, including a thorough survey of the catalysis and kinetics of the reactions, was published in 1962 [116]. Other relatively recent surveys of the subject of special interest include those of Farkas and Mills [117] and Lyman [118]. Other reviews which are of special supplemental value with respect to control of the reactions in polyurethane formation include those of Johnson [119] and Saunders and Frisch [120]. 

IR spectroscopic evidence for covalent urethane bond formation in the reaction between isocyanates and wood has been obtained. Isolation of holocellulose by the sodium chlorite method, isolation of lignin by the H2SO4 procedure, and subjecting both to IR spectroscopy indicated that isocyanates reacted with both cellulose and lignin (194),... 

The reactions of 2-aminobenzimidazoles have been reviewed <83S86l>. The compounds form Schiffs bases with carbonyl compounds, with isocyanates and isothiocyanates they give ureas and thioureas, they are subject to 1,3-dipolar addition reactions, and to the formation of carbamates on acylation and aroylation. When aminoimidazoles are acylated there is frequently competition between the annular and exocyclic nitrogen (see above). Add chlorides and anhydrides (soft) acylate the amino group chlorocarbonic acid esters (hard) are specific for the heteroatom <84CHE204>. When heated, the A -acyl products isomerize (Scheme 91). 

The formation and reactivity of surface intermediates over three-way catalysts are important subjects in designing automobile exhaust catalysts. The high temperature NO-CO and NO-CO-O2 reactions produce isocyanate surface intermediates (-NCO) and release N2O intermediate products depending on, for example, how the catalyst surface is pretreated before the NO and CO adsorption [2]. Infrared spectroscopy is an excellent tool to investigate the formation of these kind of surface intermediates. With IR very low concentrations of surface compounds can be detected under reaction conditions. 

End-Group Analysis. In end-group analysis the concentration of an end group is measured by a suitable technique, and then, from the known structure of the polymer, the value for Mn may be calculated (10-15). In condensation polymers one end of the polymer should have a specific group that can be titrated by appropriate means. Polyesters (13), polyamides (13), and polyurethanes (16) have been subjected to this analysis. Polyethers have been analyzed by hydroxyl-group titrations similar to those used for polyesters or by reaction with excess phenyl isocyanate followed by reaction with excess di-n-butylamine the latter was back-titrated with perchloric acid (17). Nonaqueous titrations (18) have been used to... 

From a practical point of view, isocyanates, together with carbamates and ureas (Chapter 3), are the most important organic products discussed in this book. Their synthesis from nitroarenes has indeed been the subject of many patents. There are also limited examples of aliphatic isocyanates obtained by this route. Organic mono- and diisocyanates may be prepared in a continues liquid phase method by treating the appropriate amine with phosgene. However, the reaction is rather complex [6] and, besides the use of the dangerous phosgene, the formation of the corrosive hydrochloric acid creates several problems. Aliphatic isocyanates can also be obtained from olefins with isocyanate ion in the presence of a salt of a coordination compound of palladium or platinum [7], from olefins with isocyanic acid in the vapour phase over Pt/ALOs [8], and from formamides, by oxidation over a silver catalyst [9]. Apparently only the last reaction seems to have some potential practical applications [10]. 

Synthesis of BMY-14802 (228) commenced from pyrimidine derivative 243 which reacted with piperazine 244 to give derivative 245 (Scheme 58) [215, 216]. Reduction of the compound 245 followed by deprotection gave amine 246, which was alkylated with chloride 247 and then subjected to acidic hydrolysis to form ketone 248. Reduction of 248 allowed BMY-14802 (228) to be obtained. Pure enantiomers of 228 were also obtained. To achieve this, the following methods were used resolution of 228 with using reaction with a-phenylethyl isocyanate [217] or lipase-catalyzed acetylation or hydrolysis [218], alkylation of 245 with enantiopure alcohols 249 [219] and microbial reduction [305] or Ru-catalyzed enantioselective hydrogenation [220] of 248. 

D. Pseudohalogeno-derivatives.—Little work has been carried out in this area. Isocyanates of cyclic phosphazenes, previously unknown, are thought to be formed in the reaction of NgPaBrg with AgOCN in nitro-methane. They were detected by i.r. spectroscopy, and underwent ready polymerization, which precluded their isolation. On the other hand, isothiocyanates, [NP(NCS)2] (n = 3 or 4), are well known and a detailed study of their spectra has been reported. The azide, N3Pa(N3)8, has been the subject of an i.r. study which suggests that the molecule has Z)3A symmetry. 

Arylazo-4-(3-ethoxycarbonylureido)furoxans 62, which were synthesized by the reactions of 4-amino-3-arylazo-furoxans with ethoxycarbonyl isocyanate, were subjected to cascade rearrangements under the action of potassium r/-butoxidc in dimethylformamide or by heating in dimethyl sulfoxide to form 4-amino-2-aryl-5-nitro-2//-l,2,3-triazoles 63 (Scheme 13) <2001MC230, 2003RCB1829>. 

A theoretical study of the reaction of water and methanol with HNCO has led to a prediction of a four-centred transition state for both reactions. The interactions of water and of alcohols with alkyl isocyanates have been the subject of both experimental and theoretical study. In the case of hydration, evidence for initial interaction of water and water clusters (n = 1-3) across the N=C bond of the alkyl isocyanate... 

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