We began our study with hydroboration of phenylacetylene (1) with 1.1 eq. of 4,4,5,5-tetramethyl-1,3,2dioxaborolane (pinacolborane, HBpin) using sodium triethylborohydride as a catalyst and without any additional solvent. It has to be noted, however, that all the borohydrides were supplied and used as 1M solutions in either toluene or THF. The results of the reaction conditions screening are presented in Table . A portion of 10 mol % of NaHBEt3 (1M in toluene) applied in the model reaction led to 71% conversion of 1 after 1 h at 60 °C, and yielded exclusively monoborylated linear (E)-alkenyl boronate ester 2 (entry 7). The prolonged reaction time of 24 h gave higher conversion of 1 (93%, entry 6). Increasing the reaction temperature to 80 °C resulted in complete conversion of 1 within 1h affording product 2 with as high anti-Markovnikov regioselectivity as previously (>99%, entry 5). Decreasing the catalyst loading to 5 mol% of NaHBEt 3 resulted in a decrease in reactivity: after 1h at 80 °C, only 87% conversion of 1 was observed (entry 4). The reactions carried out with an addition of solvents, such as toluene, THF or dioxane, led to lower conversions of 1 (83-85%) (entries 10-12). Interestingly, two additional experiments performed with 2.2 equivalents of HBpin, with and without addition of toluene, both led to drastic reduction of phenylacetylene conversion and formation of two by-products: the alkyl boronate ester 3 and alkyl bisboronate ester 4 (entries 13-14).