The chemistry of organoazides is exceedingly rich, since the azide functionality reacts with electrophiles, nucleophiles, and dipolarophiles, with or without the extrusion of dinitrogen (Figure 1). Common place transformation such as Staudinger reductions or ligations, Cu(I)-catalyzed Huisgen cycloadditions (of the “click” reaction family), Curtius or Schmidt rearrangents, nitrene reactions, or imine formation via aza-Wittig reactions all necessitate organoazide precursors or intermediates (Scheme 1).1
Scheme 1.Curtius or Schmidt rearrangents, nitrene reactions, or imine formation via aza-Wittig reactions all necessitate organoazide precursors or intermediates
The most common route to alkyl azides uses a substitution reaction of primary or secondary alkyl halides with inorganic azides, or via hydroazidation of alkenes. The latter case, however, is limited to those olefins which give stabilized carbocations and requires the use of somewhat dangerous hydrazoic acid, HN3 or the safer alternative, TMSN3. Carreira and co-workers recently reported the Co(II)-catalyzed hydroazidation of unactivated olefins with p-toluenesulfonyl azide (TsN3) to yield alkyl azides (Scheme 2).2-4 The catalyst is easily prepared in situ from Co(BF4)2 · 6H2O and a Schiff base ligand. Mono-, di-, and trisubstituted olefins are tolerated in the hydroazidation reaction and complete Markovnikov selectivity is observed. The hydroazidation reaction exhibits good functional group tolerance, with ester and silyl ether groups surviving the reaction conditions without issue. Additionally, the in situ-generated alkyl azides can be directly converted to amines (via reduction) or triazoles (via Cu(I)-catalyzed cycloaddition) in a one-pot process.
Scheme 2.Carreira and co-workers recently reported the Co(II)-catalyzed hydroazidation of unactivated olefins with p-toluenesulfonyl azide (TsN3) to yield alkyl azides
We are pleased to offer the precursors to this useful catalyst, in addition to a variety of other reagents for azide formation.