Science of Synthesis

Corcé, V.; Lévêque, C.; Ollivier, C.; Fensterbank, L., Science of Synthesis: Photocatalysis in Organic Synthesis, (2018) 1, 463.

Nickel-mediated cross-coupling reactions involving isocyanates as electrophiles for the formation of amides have not been extensively developed. Serrano and Martin report a method for the electrophilic cross coupling of alkyl bromides with isocyanates by using a nickel(II) catalyst.[‌55‌] Inspired by this work, the Molander group has engaged such electrophiles with alkylsilicates under photoredox/nickel dual catalysis conditions.[‌56‌] A catalyst system comprising dichloro(1,10-phenanthroline)nickel(II) {[NiCl2(phen)]; phen = 1,10-phenanthroline} (2.5 mol%) and tris(2,2′-bipyridyl)ruthenium(II) bis(hexafluorophosphate) {[Ru(bipy)3](PF6)2; bipy = 2,2′-bipyridyl (‌13‌), 1.5 mol%} as the photocatalyst enables the coupling reaction between cyclohexylsilicate ‌70‌ and isocyanates ‌71‌ to give amides ‌72‌ in moderate yields. The reaction tolerates a wide range of isocyanates. Primary, secondary, and tertiary alkyl isocyanates bearing functional groups such as ester, alkoxysilane, and alkenyl moieties are suitable electrophiles, as are substituted aryl isocyanates. Isothiocyanates can also provide the corresponding cross-coupling products (‌Scheme 32‌). The use of other functionalized alkylsilicates extends the scope of the product amides ‌73‌ (‌Scheme 33‌).

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References