GC monitoring of the reaction revealed full consumption of 1a within 3 h (a kinetic profile is provided in the SI, Figure ). Upon reaction progress, 1c was detected as intermediate (ca 10%) which rapidly isomerizes to the corresponding E-alkene (1b). There was no evidence of overreduction to afford the corresponding alkane after 20 a Reaction conditions: diphenyl acetylene (1a) (0.9 mmol, 1 equiv), KBH4 (0.5 equiv), MeOH (3.7 mL, 100 equiv), 60 °C, 20 h, yields determined by by GC-MS using dodecane as internal standard. b Isolated yields. c 45 °C. d 35 °C. e H2 (30 bar) in the absence of KBH4. f Addition of H2O (200µL).