Scheme 4. Time-stacked in situ³¹P NMR spectra of the borylation of 4d by HBpin as in Scheme 2 (CD₃CN, 202 MHz, 60 °C) at the following time points: (a) 0 min, (b) 15 min, (c) 30 min, (d) 1 h, (e) 3 h, and (f) 5 h, showing 1 (δ 159.7 ppm), 2 (δ 85.4 ppm), and 3 (δ 147.0 ppm).