Regioselectivity of the Chan–Lam coupling of ambident nitropyrazoles with trans-styrylboronic acid

Regioselectivity of the Chan–Lam coupling of ambident nitropyrazoles with trans-styrylboronic acid depends on the base and catalyst nature and can vary the N(1)/N(2)-isomer ratio from ∼2 : 1 to ∼1 : 2. 2-Methyl-4-nitro- and 2,4-dinitroimidazoles are unreactive in this reaction. The structure of N(1)/N(2) isomers was elucidated by NOE measurements and by the comparison of experimental and DFT calculated 13C NMR chemical shifts.