Figure 4: Chemoselective cross-couplings of bis- and tris-borylated chiral aromatics.
From: Iterative protecting group-free cross-coupling leading to chiral multiply arylated structures
(a) Initial selective coupling of aryl B–C bonds using Pd/PtBu3 as the catalyst and carbonate bases, followed by second, stereospecific coupling of chiral secondary benzylic B–C bond leading to biphenyl-substituted 1,1–diaryl alkanes. (b) The introduction of three unique aryl groups sequentially by coupling at (1) the aryl B–C bond, (2) the linear achiral aliphatic B–C bond, and (3), the chiral benzylic B–C bond in a single pot for the first two steps, and the use of filtration through a short silica plug before the final step. (c) Illustration of the orthogonal coupling concept in the synthesis of phosphodiesterase inhibitor CDP 840 (14).
