Reactions with Isocyanates

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

Isocyanates iasert iato RO and RN bonds. CycHc ethers, such as oxiranes, are known to undergo reactions with isocyanates to form 2-oxa2oHdinones ia high yield (38—40). 

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. 

H-pyran synthesis from, 3, 759 bis(trimethylsiloxy) in pyrrole synthesis, 4, 333 chromene synthesis from, 3, 750 cycloaddition reactions with isocyanates, azetidin-2-ones from, 7, 261 dihydropyran synthesis from, 3, 771 fuiyl... 

The dimeric tellurium diimide 10.7 undergoes a cycloaddition reaction with BuNCO to generate the Ai,iV -ureatotellurium imide 10.11, which is converted to the corresponding telluroxide 10.12 by reaction with excess BuNCO. " By contrast, BuN=S=N Bu undergoes exchange reactions with isocyanates. 

Cycloadditions of isocyanates and their derivatives with vinyiaziridines were first reported by Alper and coworkers. From their previous studies of cydoadditions to vinylepoxides or alkylaziridines, they investigated cydoadditions to vinyiaziridines and found that such reactions with isocyanates, carbodiimides, or isothiocyanates in the presence of catalytic amounts of Pd(OAc)2 (2 mol%) and PPh3 (10 mol%) at room temperature afforded five-membered ring products 249 in 34—97% yields (Scheme 2.61) [91]. When an aziridine 247 possessing an alkyl substituent at the... 

Impurities in CL have also been destroyed by oxidation with ozone22 followed by distillation. Ozonation treatment of waste CL leaves no ionic impurities. However, the most commonly used oxidizing agents are potassium permanganate, perboric acid, perborate, and potassium bromate. Treatment of CL with these oxidizing agents is carried out in a neutral medium at 40-60°C. Strongly alkaline or acidic conditions accelerate the oxidation of CL to form isocyanates. Hie undesirable oxidation reaction is fast above pH 7 because of the reaction with isocyanate to form carbamic acid salts, which shifts the equilibrium to form additional isocyanate. 

Methyl 3-(triphenylphosphoranylideneamino)pyrazine-2-carboxylate 33 has been synthesised and used to obtain pteridines 34, 35 by reaction with isocyanates followed by adding alcohols or amines (Scheme 5)<96JCS(P1)247>. 

Polyether-based foams account for more than 90% of all flexible polyurethane foams. The properties of foams are controlled by the molecular structure of the precursors and the reaction conditions. In general, density decreases as the amount of water increases, which increases the evolution of carbon dioxide. However, the level of water that can be used is limited by the highly exothermic nature of its reaction with isocyanate, which carries with it the risk of self-ignition of the foamed product. If very low density foams are desired, additional blowing agents, such as butane, are incorporated within the mixing head. 

A library of l,3,7-substituted-perhydropyrazino[l,2-f]pyrimidine-2,6,8-triones was built by preparation of functionalized ketopiperazines on the solid phase, followed by N-acylation with 2-bromoacetic acid, reaction with isocyanate and with concomitant cyclization using trifluoroacetic acid (TFA) <2003W02003/013740>. 

The amine 166 undergoes a reaction with isocyanate to produce the urea derivative 167 (Equation 11) <2005BML3778>. 

Scheme 18). Three reactions at OH-2 were investigated, namely carbamatations by reaction with isocyanates, etherifications by reaction with alkyl bromides, and substitution by an azide after intermediate triflate formation. 

Reactions with Isocyanates. The reaction of alcohols with isocyanates to form carbamates is well known and similar reactions with poly(vinyl alcohol) would be expected. Until recently, the only available reaction conditions were to use a heterogeneous reaction mixture or to run the reaction in a poor solvent for poly(vinyl alcohol). The best poly(vinyl alcohol) solvents, water and formaide derivatives, react rapidly with isocyanates. Nevertheless, several such reactions have been run in the past and we will cite only a few of them. A potentially photosensitive polymer was made by the reaction of allyl isocyanate with poly(vinyl alcohol) (57) and several workers have crosslinked poly(vinyl alcohol) with hexamethylene diisocyanate (58.59). 

Surface Concentration of Hydroxyl Groups. Since it has been concluded that the urethanation with monoisocyanates in toluene is limited to the hydroxyl groups present at the film surface, we can evaluate the concentration of the hydroxyl groups that are present at the surface, more strictly, accessible to the reaction with isocyanates. The amounts of hydroxyl groups urethanated to saturation, obtained from Figures 7, 9 and 11 are summarized in Table I, which also contains the values obtained from experiments not shown here. These are expressed as surface concentration per cm of films, which are assumed to have a perfectly flat... 

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

Reaction with isocyanates is also observed in derivatives having a free hydroxyl at C-4. Reaction of 4-deacetylvinblastine (98) under conditions identical to those employed in the preparation of 96 affords the mixed... 

The weak nucleophilic nature of polynitroaliphatic alcohols is also reflected in their slow reactions with isocyanates to yield carbamates. These reactions often need the presence of Lewis acids like ferric acetylacetonate or boron trifluoride etherate. The reaction of bifunctional isocyanates with polynitroaliphatic diols has been used to synthesize energetic polymers.33°... 

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