A highly regioselective hydroselenation of terminal alkynes with benzeneselenol can be achieved by the combination of palladium acetate and pyridine, providing the corresponding terminal alkenes, (i.e., 2-phenylseleno-1-alkenes) as a sole product. In this hydroselenation, pyridine may act as a suitable ligand for active palladium intermediates.

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This paper is dedicated to Professor Juzo Nakayama on the occasion of his 65th birthday and retirement.The reaction of benzenethiol (or diphenyl disulfide) with cyclohexylallene, as a representative terminal allene, has been investigated in detail in the presence of transition metal-phosphine complexes as the catalyst. Pd(PPh 3 ) 4 -catalyzed hydrothiolation of cyclohexylallene with benzenethiol in acetonitrile affords the corresponding terminal vinylic sulfide [RCH 2 C(SPh)=CH 2 (R = c Hex)] regioselectively in good yield, whereas Pt(PPh 3 ) 4 -catalyzed hydrothiolation of cyclohexylallene gives the regioisomeric vinyl sulfide successfully. Similar hydrothiolation of the allene proceeds using diphenyl disulfide, instead of benzenethiol, in the presence of triphenylphosphine and water.