Organic heteroatom compounds including the organophosphorus compounds play an important role in many fields such as the organic synthesis,catalysis,biochemistry,and material science.In previous studies,we have developed a series of regio- and stero-selective Markovnikov and anti-Markovnikov addition of P(O)-H bonds to unactivated alkynes and alkenes.1 Although the addition of P(O)-H compounds to terminal alkynes usually gave anti-Markovnikov regioisomers (β-adducts in the parenthesis) in excellent selectivities,the preparation of the Markovnikov α-adducts is usually accompanied by formation of the β-adducts,which can even become the major product when bulky substrates are used.By using a new oxapalladacycle catalyst that was conveniently prepared via direct ortho palladation of diphenylphosphinic acid with palldadium acetate and with its structure determined by X-ray analysis,the Markovnikov-type additions of E-H bonds (P(O)-H,S-H and spC-H) to alkynes can proceed with high selectivities (up to 99/1),even with the bulky substrate such as t-butyl acetylene,to afford high yields of the α-adducts.2 Mechanistic studies of the addition of Ph2P(O)-H to alkynes revealed that the reaction proceeds via a unique catalytic cycle.