Alkynylboronates and ‐boramides in Co^I‐ and Rh^I‐Catalyzed [2+2+2] Cycloadditions: Construction of Oligoaryls through Selective Suzuki Couplings

Abstract

Abstract Oligoaryls were prepared through transition‐metal‐catalyzed [2+2+2] cycloadditions of borylated alkynes, followed by Suzuki cross‐couplings with aryl halides. Ethynylboryl pinacolate took part in cobalt‐catalyzed [2+2+2] cycloadditions of all types investigated (i.e., all‐intermolecular cyclotrimerization, diyne‐yne cocyclization, and all‐intramolecular triyne cycloisomerization). The resulting platforms gave rise to linear and angular ter‐ and quateraryls after Pd‐catalyzed cross‐coupling. In addition, the first [2+2+2] cycloadditions involving alkynyl naphthaloboramides were developed. These derivatives could be cocyclized with diynes in the presence of a rhodium complex as catalyst. Because the boramide group is inactive under Suzuki coupling conditions, but can be readily deprotected to afford an active one, an iterative functionalization of a boronate‐/boramide‐substituted benzene could be achieved.