Aryl N-methyliminodiacetic acid (MIDA) boronates from cyclotrimerization of ethynyl MIDA boronate with diynes

Cyclotrimerizations of ethynyl N-methyliminodiacetic acid (MIDA) boronate (1) with 1,6-diynes 2 have been studied, using three different catalysts (based on ruthenium, rhodium, and iridium) and variable reaction conditions. Successful cyclotrimerization reactions were obtained with both Cp*RuCl(cod) and Rh(cod)2BF4/BINAP as pre-catalysts in THF or acetone. Ruthenium-catalyzed cyclotrimerization of an unsymmetrically bromo-substituted diyne (2f) with 1 was successfully scaled up (2 g) and included in a total synthesis strategy toward potential selective inhibitors of tyrosine kinase 2.