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18.2.4.1.12.1 Variation 1: Addition of Isocyanic Acid

DOI: 10.1055/sos-SD-018-00070

Braverman, S.; Cherkinsky, M.; Birsa, M. L.Science of Synthesis, (200518122.

In general, alkenes react with isocyanic acid with difficulty; however, introduction of electron-donating substituents increases the reactivity toward isocyanic acid significantly. For example, α,β-unsaturated ethers, such as butyl and ethyl vinyl ethers, vinyloxyethyl methacrylate, and butyl isopropenyl ether, produce α-alkoxy isocyanates, e.g. 147, in good yields (Scheme 83).[‌405‌‌407‌] An excess of isocyanic acid is required in order to avoid the side reaction of polymerization of the unsaturated ethers. Under heating and in the presence of a catalyst (4-toluenesulfonic acid, boron trifluoridediethyl ether complex, iodine) some other substrates, including isobutene, isoprene, styrene, and α-methylstyrene, can add isocyanic acid, generated in situ from cyanuric acid.[‌408‌] Bicyclic alkenes, including norbornene, 2-ethylidenenorbornane, norbornadiene, and dicyclopentadiene, react with isocyanic acid at 120°C in the presence of 4-toluenesulfonic acid to give the corresponding isocyanates.[‌409‌]

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