Isocyanate dimerization hydrogen

The aliphatic-aromatic isocyanate dimer 5 is obtained in the cyclization of the corresponding allophanoyl chloride in the presence of pyridine as the hydrogen chloride scavenger. Allophanoyl chlorides are readily obtained from aliphatic or aliphatic/aromatic ureas and phosgene. ... 

The synthesis of the module is provided in Scheme 10.5 (Kushner et al. 2007). Double alkylation of ethyl acetoacetate followed by guanidine condensation afforded alkenyl-pyrimidone intermediate 24 (Kushner et al. 2007). Isocyanate 25 was coupled to pyrimidone 24 to yield 26. Upon dimerization in DCM, RCM effectively cyclized the two UPy units (Mohr et al. 1997 Week et al. 1999). A one-pot reduction and deprotection through hydrogenation using Pearlman s catalyst gave diol module 27. Finally, capping 27 with 2-isocyanatoethyl methacrylate at both ends provided the UPy sacrificial cross-linker 28, which was thoroughly characterized by H- and C-NMR, Fourier transform IR (FTIR), and mass spectrometry. 

Just to illustrate the real synthetic interest of these heterocyclobutadienes, it appeared that trimethylsilyl isocyanate inserts into the P-N bond of 28 leading to 38, which after hydrolysis afforded 39 in 50 % yield. Interestingly, 39 exists as a hydrogen-bonded dimer in the solid state and has a structure very similar to that of cytosine, the C(NH2) being replaced by a P(N/Pr2)2 group it could be considered as a labelled cytosine (Scheme 15). 

MDI Chemistry. Methylene diphenylene isocyanates are a product of the reaction of aniline, formaldehyde and phosgene. The first step is the reaction of aniline (made by hydrogenation of nitrobenzene) with formaldehyde to form the intermediate bis(aminophenyl)methane. The chemistry is shown in Eq. (2). The bis(aminophenyl)methane is then reacted with phosgene to yield dimeric and trimeric isocyanates as shown in Eq. (3) [4]. 

The ready availability of bis-isocyanates makes dimers of modules 71 and 75 straightforward to synthesize. Meijer and co-workers have pioneered this approach [49] to create hydrogen-bonded, supramolecular polymers of considerable size and molecular weight (see Sect. 4). A different dimeric... 

Acrylic/styrene/acrylonitrile terpolymer Allyl isocyanate Azelaic acid t-Butyl cumyl peroxide 4-t-Butyl-o-thiocresol Dimer acid, hydrogenated Dipentene-styrene resin t-Hexadecanethiol 1-Hexene n-Hexyl acrylate... 

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