Catalytic undirected borylation of tertiary C–H bonds in bicyclo[1.1.1]pentanes and bicyclo[2.1.1]hexanes

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Abstract
Catalytic borylations of sp3 C–H bonds occur with high selectivities for primary C–H bonds or secondary C–H bonds that are activated by nearby electron-withdrawing substituents. Catalytic borylation at tertiary C–H bonds has not been observed. Here we describe a broadly applicable method for the synthesis of boron-substituted bicyclo[1.1.1]pentanes and (hetero)bicyclo[2.1.1]hexanes by an iridium-catalysed borylation of the bridgehead tertiary C–H bond. This reaction is highly selective for the formation of bridgehead boronic esters and is compatible with a broad range of functional groups (>35 examples). The method is applicable to the late-stage modification of pharmaceuticals containing this substructure and the synthesis of novel bicyclic building blocks. Kinetic and computational studies suggest that C–H bond cleavage occurs with a modest barrier and that the turnover-limiting step of this reaction is an isomerization that occurs prior to reductive elimination that forms the C–B bond.
Funding Information
  • National Science Foundation
  • U.S. Department of Health & Human Services | National Institutes of Health (R35GM130387, S10OD023532)

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