A Ph2P(O)-protected allcyne underwent dephosphorylation by treatment with MeMgBr in THF with Me3Si-protection untouched. The dephosphorylation followed by a transition-metal-catalyzed coupling of the resulting terminal alkyne with aryl halides was carried out in a one-pot manner to afford the desired coupling product. Selective deprotection of Me3Si-Ph2P(O)-protected alkynes enabled facile syntheses of expanded pi-systems such as cyclic phenyleneethynylenes and unsymmetrically substituted ditriazol.