A facile catalytic protocol achieves the homocoupling of pyrazole boronic esters, enabling access to the structurally-flexible metal–organic framework Co(bpz).
Abstract
The iridium-catalyzed C-H borylation of diethyl phenylphosphonate results in nonselective mono and bisborylation to afford a near statistical mixture of 3-, 3,5- and 4-boryl substituted aryl phosphonates whereas 3-substituted aryl phosphonates undergo highly regioselective C-H borylation to afford the corresponding meta-phosphonate substituted arylboronic esters as the sole product; the resulting boronic esters were used as nucleophilic reagents in a subsequent palladium-catalyzed Suzuki–Miyaura cross-coupling to generate a range of biarylmonophosphonates. Gratifyingly, the Suzuki–Miyaura cross-coupling can be conducted without purifying the boronic ester which greatly simplifies the synthetic procedure.
Graphical Abstract
The Synthesis of Biarylmonophosphonates via Palladium-Catalyzed Phosphonation, Iridium-Catalyzed C-H Borylation, Palladium-Catalyzed Suzuki–Miyaura Cross-Coupling