Urethans diol carbamates

Compounds containing the O-H group such as diols will, under the appropriate conditions, react with isocyanates to give a urethane or, in pure organic literature, a carbamate. Secondary alcohols react at about one-third the rate of primary alcohols. Complex alcohols react very slowly with isocyanates and form a mixture of urethanes and olefins. 

Diimide reduction of 96, obtained by the enzymatic oxidation of 95 (96% ee) [67], followed by O-acetylation afforded cyclohexene-diol 97 in 47% yield (Scheme 19). Compound 97 was converted into carbamate 98 by S 2 reaction with methylamine and subsequent urethane formation. Regioselective protection of the diol in 98 with TBSC1 afforded 99, which was coupled with bromoisovanillin 54 under the conditions of Mitsunobu to provide 100 (see Sect. 2.2.2). The intramolecular Heck reaction of 100 constructed the benzofuran ring including a quaternary center to afford 101 in 82% yield. Wittig reaction of 101 with Ph3P=CHBr generated vinyl bromide 102 in 49% yield as a mixture of E- and Z-isomers (E Z = ca. 1 2). 

Diisocyanates are an important class of chemicals of commercial interest, which are frequently used in the manufacture of indoor materials. such as adhesives, coatings, foams and rubbers (Ulrich, 1989). In some types of particle board, the diisocyanates have replaced formaldehyde. Isocyanates are characterized by the electrophilic -N=C=0 group, which can easily react with molecules containing hydroxy groups, such as water or alcohols. On hydrolysis with water, primary amines are formed, while a reaction with alcohols leads to carbamates (urethanes). Polyurethane (PUR) products are then obtained from a polyaddition of diisocyanate and diol components. Compounds commonly used in industrial surface technology are 4,4 -diphenylmethane diisocyanate (MDI) and hexamethylene diisocyanate (HDI). The diisocyanate monomers are known as respiratory sensitizers and cause irritation of eyes, skin and mucous membrane. Therefore, polyisocyanates such as HDI-biuret and HDI-isocyanurate with a monomer content <0.5 % are used for industrial applications, and isocyanate monomers will not achieve high concentrations in ambient air. Nevertheless, it is desirable to measure even trace emissions from materials in private dwellings. 

The bis(4-diphenylmethaneurethanes), Urethane-n, were either synthesized by a separate method starting from 4-hydro-xybutyIdiphenylmethane-4-carbamate or similar to POTM-n-Urethane synthesis by reacting the Diol-n with 4-diphenylme-thaneisocyanate. 

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