First propargyl azides bearing strong acceptor substituents and their effective conversion into allenyl azides: Influence of the electronic effects of substituents on the reactivity of propargyl azides

We have succeeded in the synthesis of propargyl azides containing 1- or 3-phenylthio functionalities. The selective oxidation of their sulfur atoms to sulfoxides and sulfones allows access to the first propargyl azides bearing acceptor substituents. Interestingly, the prototropic rearrangement of the latter propargyl azides leads to the formation of allenyl azides with relatively high stabilities and with moderate to good yields. Propargyl azides containing phenylthio functionalities react in the presence of nucleophiles to afford the expected N-un-substituted 1,2,3-triazoles via short-lived allenyl azides. These results are entirely different from those of the corresponding sulfoxides and sulfones, which react under the analogous conditions either to produce the corresponding his(triazolo)pyrazine derivatives or to yield newly substituted vinyl azides. The latter compounds can successfully be used as starting material providing access to azirines. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)