Exploring benzylicgem-C(sp3)-boron-silicon and boron-tin centers as a synthetic platform

Abstract

A stepwise build-up of multi-substituted Csp3carbon centers is an attractive, conceptually simple, but often synthetically challenging type of disconnection. To this end, this report describes howgem-α,α-dimetalloid-substituted benzylic reagents bearing boron/silicon or boron/tin substituent sets are an excellent stepping stone towards diverse substitution patterns. Thesegem-dimetalloids were readily accessed, either by known carbenoid insertion into C-B bonds or by the newly developed scalable deprotonation/metallation approach. Highly chemoselective transformations of either the C-Si (or C-Sn) or the C-B bonds in the newly formedgem-Csp3centers have been achieved through a set of approaches, with a particular focus on exploiting the synthetically versatile polarity reversal in organometalloids by λ3-aryliodanes. Of particular note is the metal-free arylation of the C-Si (or C-Sn) bonds in suchgem-dimetalloidsviathe iodane-guided C-H coupling approach. DFT calculations show that this transfer of the (α-Bpin)benzyl group proceedsviaunusual [5,5]-sigmatropic rearrangement and is driven by the high-energy iodine(iii) center. As a complementary tool, thegem-dimetalloid C-B bond is shown to undergo a potent and chemoselective Suzuki-Miyaura arylation with diverse Ar-Cl, thanks to the development of the reactivegem-α,α-silyl/BF3K building blocks.