Herein, we present a new application of fluorosulfonylazide (FSO2N3) for diazotizing a series of activated methylene compounds to deliver the corresponding diazo products. Notably, by the judicious choice of bases, the selective generation of the Bestmann-Ohira reagent (BOR) or the Seyferth−Gilbert reagent (SGR) has been realized from FSO2N3 and dimethyl-2-oxopropylphosphonate. We also investigated the kinetics of the homologation of aldehydes using these two reagents with K2CO3 as a base in MeOH, finding that a faster reaction rate was achieved by using SGR. Moreover, the facile one-pot synthesis of terminal alkynes from aldehydes has been established, which could be further coupled with azides to deliver triazoles using CuAAC click chemistry.