Alkyl-alkyl substituted alkynes tend to be a challenging class of substrates in the field of semihydrogenation. Selective semihydrogenation of these substrates using manganese catalyst is rare and so far limited to dodecyne (28a) in up to 67% yield. 16d, 16e Interestingly, Mn1 was proven to be highly active also for the transformation of alkylalkyl substrates alkenes with moderate selectivity as depicted in Table . Over-hydrogenation was observed for some substrates. For instance, 4-octyne (27a) yielded 80% yield of desired product with an E/Z ratio of 2:1 ratio together with 20% of over-hydrogenated product (Table ). On the other hand, alkynes with longer aliphatic chains proved to be more successful and 6-dodecyne (28a), 7-tetradecyne (29a) and 2,9-dimethyl-5-decyne (30a) were fully converted to corresponding alkenes with 90 to 99% yields (Table ). The two isomers of 5decenol (31b) are known to be hormones of the Peach Twig Borer and the Lepidoptera, respectively, and can be encountered in different industrial formulations of pesticides and fragrances. Interestingly, the presence of a primary alcohol in the corresponding precursor 31a was tolerated and quantitatively transformed into the corresponding alkene 31b with 99% isolated yield and a 3:1 E/Z ratio (Table ). Notably, double bond migration was not observed in any case. Table . Mn1 catalyzed semihydrogenation of alkyl-alkyl alkynes a a Reaction conditions: alkyne (0.9 mmol, 1 equiv), Mn1 (2 mol%), KBH4 (0.5 equiv), MeOH (3.7 mL, 100 equiv), 90°C, 20 h, isolated yields. Values in the brackets correspond to the E/Z ratio determined by 1 H NMR spectroscopy. b Yield determined by GC-MS using dodecane as intenal standard. c Mn1 (1 mol%).