Isocyanates chiral aliphatic

Chiral aliphatic isocyanates 384, which are applied to aminopropyl columns to render them chiral for the resolution of racemic amines, alcohols, and acids as amide, urea, carbamate or hydrazide derivatives, have been prepared with triphosgene. The authors found that approximately 0.66 mol rather than 0.33 mol of triphosgene was required per mol of amine, presumably because of a loss of phosgene gas along with the HQ by-product [270]. 

Polysaccharide-based CSPs also exhibit a chiral recognition for alcohols and a large number of resolutions have been reported. Chiral alcohols can usually be directly resolved with hexane containing a small amount of an alcohol as the eluent. For aliphatic alcohols, which cannot be directly resolved, their resolution is often efficiently attained as phenylcarbamate or benzoate derivatives on OD (Figure 17).85 For example, 2-butanol and 2-pentanol are completely resolved with a very high selectivity on OD as their phenylcarbamates. The derivatization of alcohols to phenylcarbamates and benzoates can be easily achieved by the reaction with phenyl isocyanates and benzoyl chlorides, respectively. In most cases, the phenylcarbamates are better resolved than the benzoates. For chiral compounds bearing phenolic hydroxy groups, the addition of a small amount of an acid to an eluent is recommended to depress its dissociation. 

Reactions of chiral 5-(3-methyl-2-phthahmidylpentanoylamino)isophthalic acid and 5-(4-methyl-2-phthalimidyl-pentanoylartrino)isophthalic acid with several aromatic and aliphatic diisocyanates like 4,4 -methylenebis(phenyl isocyanate), toluene-2,4-diisocyanate, isophorone diisocyarrate and hexamethylene diisocyanate rmder microwave irradiation were studied by Mallakpour et al. (2008a, 2008b). The... 

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