Isocyanates reaction with epoxides

AH of the amine hydrogens are replaced when MDA or PMDA reacts with epoxides to form amine based polyols. These polyols can be used in reactions with isocyanates to form urethanes or with additional epoxide to form cross-linked thermo set resins. 

Over the last decade, a considerable number of reactions has been studied (11,35) (i) olefins oxidation (38,39), hydroboration, and halogenation (40) (ii) amines silylation (41,42), amidation (43), and imine formation (44) (iii) hydroxyl groups reaction with anhydrides (45), isocyanates (46), epichloro-hydrin and chlorosilanes (47) (iv) carboxylic acids formation of acid chlorides (48), mixed anhydrides (49) and activated esters (50) (v) carboxylic esters reduction and hydrolysis (51) (vi) aldehydes imine formation (52) (vii) epoxides reactions with amines (55), glycols (54) and carboxyl-terminated polymers (55). A list of all the major classes of reactions on SAMs plus relevant examples are discussed comprehensively elsewhere (//). The following sections will provide a more detailed look at reactions with some of the common functional SAMs, i.e hydroxyl and carboxyl terminated SAMs. 

Epoxides react with isocyanates at elevated temperatures to give 2-oxazolidinones 347 . A similar reaction is observed with phenylcarbonyl isocyanate. The reaction is catalyzed by palladium (o)-triisopropyl phosphite catalysts, lithium salt-phosphine adducts, aluminum trichloride or calcium ethoxide. The reaction can formally be regarded as interception of the thermally generated 1,3-dipolar intermediates, and it was shown that the reaction does not occur, unless the catalyst initiates ring opening... 

Primary cycloaUphatic amines react with phosgene to form isocyanates. Reaction of isocyanates with primary and secondary amines forms ureas. Dehydration of ureas or dehydrosulfuri2ation of thioureas results in carhodiimides. The nucleophilicity that deterrnines rapid amine reactivity with acid chlorides and isocyanates also promotes epoxide ring opening to form hydroxyalkyl- and dihydroxyalkylaniines. Michael addition to acrylonitrile yields stable cyanoethylcycloalkylarnines. 

An alternative route involves the reaction of 1,2-epoxides with isocyanates to yield poly-2-oxazolidones (Figure 27.12). 

Reactive organic chemicals can be bonded to cell wall hydroxyl groups on cellulose, hemicelluloses, and lignin. Much of our research has involved simple epoxides (1 3) and isocyanates (4), but most of our recent effort has focused on acetylation. Acetylation studies have been done using fiberboards (5f6), hardboards (7 11) particleboards (12-20), and flakeboards (21-23), using vapor phase acetylation (8,2 257, liquid phase acetylation (, ), or reaction with ketene (28). 

Takatsuki and co-workers have recently introduced the 3, 5 -0-sulfinyl group which has the dual purpose of protection and activation in nucleoside chemistry. For example, compound 13, prepared by protection of 12 as shown in Scheme 3, underwent reaction with benzyl isocyanate followed by intramolecular displacement of the sulfmate to give the product 14 <2004TL137>. A similar approach has also been used to prepare thioglycoside epoxides <2004CAR2895>. 

This section deals with additives used to initiate and accelerate reactions of isocyanates and epoxides. Polyurethanes are very versatile materials, capable of being formulated into a wide variety of products (B-64MI11501, B-78MI11504, B-71MI11500). Many important applications involve the production of foams catalysts play a key role in balancing the rates of the various reactions involved. 

Various unsaturated compounds, such as CO2, isocyanates and aldehydes, undergo Pd-catalysed cycloaddition with vinyl epoxides. Reaction of CO2 with 127 affords cyclic carbonates 128 with retention of the configuration at C(3), offering a method of cis hydroxylation of epoxides [66], and has been used for the synthesis of the side-chain unsaturated (—)-exo-brevicomin (129) [67], The tetrahydrofuran 131 was prepared by [3+2] cycloaddition of activated alkenes such as benzylidene malononitrile (130) with vinyl epoxide via Michael addition and allylation [68],... 

The optimum reaction conditions for reaction with epoxides are a 95/5 (v/v) mix of epoxide with triethylamine at 120°C and 150 psi nitrogen. Depending on the isocyanate used, reaction conditions of 120°C and 150 psi with no catalyst and 5 percent triethylamine or 5-35 percent dimethylformamide are optimum. 

Lithiation of compound 560 with s-BuLi-TMEDA in THF at —78 °C following an inverse addition protocol provided the anion 561. It reacts with primary alkyl iodides and triflates, silyl chlorides, diphenyl disulfide, epoxides, aldehydes, ketones, imines, acyl chlorides, isocyanates and sulfonyl fluorides to yield the expected compounds 562 (Scheme 152). The transmetallation of compound 561 with ZnBr2 allowed the palladium-catalyzed cross-coupling reaction with aryl and vinyl bromides837. When the reaction was quenched with 1,2-dibromotetrafluoroethane, the corresponding bromide 562 (X = Br) is obtained838. 

Analogous reactions of acyclic vinyl epoxides 15 with 4-toluenesulfonyl isocyanate also proceed with complete retention of configuration55. Enantiomerically pure epoxides such as 15b and c are readily available and reductive removal of the 4-toluenesulfonyl substituent from 16 is easily achieved. The transformation of 15c to 2-oxazolidinone 16c was used as the key conversion in a short enantioselective synthesis of acosamine55. 

Another standard method for the synthesis of 2-oxazolidinones is by reaction of epoxides with isocyanates. Although 4,5-disubstituted derivatives are not readily accessible by this route, it has been shown that iminodioxolanes (192) add to epoxides in the presence of AICI3 to afford these oxazolidinones in high yield <9lJOC2684>. The reaction proceeds through a spirocyclic intermediate (193) (Scheme 96). The reaction of vinyl epoxides with aryl isocyanates is facilitated by palladium catalysis (Equation (28)) <89TL3893>. The products are obtained by a double inversion process, but... 

The second type of composition is exemplified by a wide variety of acrylate- or methacrylate-ester derivatives of conventional ink vehicles combined with a photoinitiator 1. The reaction product of tung oil fatty acids, glycidyl methacrylate, -benzoquinone, and 2-methyl-imidazole mixed with tung oil and treated with tolylene diisocyanate, combined with benzoin methyl ether (26) 2. Glycerol-linseed oil-isophthalic acid alkyd reacted with isocyanate-containing prepolymer (formed by reaction of tolylene diisocyanate, -henzoquinone, 2-hydroxypropyl acrylate in ethyl acetate solution) using dibutyltin diacetate catalyst, combined with tung oil, synthetic varnish, and benzoin methyl ether (27) 3. Epoxidized... 

Isocyanates have some important reactions without the participation of active hydrogen compounds. These reactions, of real importance in polyurethane chemistry are dimerisation, trimerisation, formation of carbodiimides and reaction with epoxides and cyclic anhydrides. 

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