The present invention discloses novel methods for the synthesis of oligonucleotides and nucleoside phosphoramidites. The methods are based on employing aryl-substituted 5-phenyl-1H-tetrazoles with perfluoroalkyl groups on the aromatic ring as activators. In one aspect the novel activators are used in the synthesis of oligonucleotides via the phosphoramidite approach. In this aspect the activators are highly efficient and can be applied with very short coupling times. In a further aspect, the activators of the invention are used in the synthesis of phosphoramidites through the reaction of nucleosides comprising a free hydroxyl group with phosphitylating agents. In this aspect the activators provide very pure phosphoramidites under mild conditions. The activators of the invention are further characterized by being highly soluble, non-hygroscopic and non-hazardous.