A process for the phosphitylation of an alcohol or thiol with a phosphitylation agent in the presence of an activator is provided. The activator has the formula: ##STR00001## wherein p is 0 or an integer from 1 to 4 and R for each occurrence is a substituent. Preferably X.sup.7 is O and p is 0. The activator is commonly employed as a salt complex with an organic base. Preferred alcohols or thiols include nucleosides and oligonucleotides. The process is particularly suited for the synthesis of phosphoramidites.