Cross-Coupling Reactions of Alkylsilicates (continued)

A mild, redox-neutral direct alkylation of imines with alkylsilicates was accomplished with the organic photocatalyst 4CzlPN rather than the more common Ru or Ir-based photocatalysts. The conditions for the alkylation are mild and provide the product in high yield. The method nicely avoids the potential chain-terminating dimerization of the generated radicals by virtue of their being generated in low concentration. Interestingly, lacking the presence of a Ni catalyst, aryl bromides were tolerated under the reaction conditions. Although the majority of examples used cyclohexylsilicates, other primary and secondary alkylsilicates gave excellent results with a variety of N-protected imines (Scheme 12) 15 examples: 43 – 73%).¹²

Taking advantage of the tolerance for an aryl bromide a two-step sequence of alkylation of an imine functionality followed by an alkylsilicate cross-coupling led to a 46% overall yield of 8 (Scheme 13).¹²

Alkylsilicates reacted with isocyanates under Ni/photoredox-catalyzed conditions to give excellent yields of the amidated alkyl group. The authors propose a Ni-isocyanate adduct as an intermediate in the reaction (Scheme 14).¹³