An innovative and efficient synthesis of stable isotope labelled 1‐methyl‐5‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐1H‐pyrazole via [13C42H3] N‐methylpyrazole

In support of a programme to develop a treatment for cancer, a stable isotope labelled version of the drug candidate was required. The key labelled intermediate was [¹³C₄²H₃] N‐methylpyrazole prepared by a novel bisacetal cyclisation. This was prepared from commercially available diethyl [¹³C₃] malonate and [¹³C²H₃] iodomethane. Copyright © 2012 John Wiley & Sons, Ltd.