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P=N Bond Formation

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Under iron catalysis, a hydroxylamine-derived triflic acid salt oxidizes phosphines to a wide range of iminophosphorane triflic acid salts. Diphosphines afford phosphine-iminophosphoranes that can serve as ligands in transition metal complexes. The developed method can be employed in the synthesis of mixed diiminophosphoranes and in a traceless Staudinger ligation.
E. Falk, A. Franchino, T. Horak, L. Gürtler, B. Morandi, Org. Lett., 2023, 25, 1695-1700.

FeCl2 catalyzes a facile imidization of phosphines with N-acyloxyamides to provide synthetically useful N-acyliminophosphoranes with high functional group tolerance. The transformation can be scaled up to gram scale with a catalyst loading of 1 mol%. The iminophosphoranyl moiety is an effective directing group for Rh(III)-catalyzed ortho C(sp2)-H bond amidations.
S. Lin, B. Lin, Z. Zhang, J. Chen, Y. Luo, Y. Xia, Org. Lett., 2022, 24, 3302-3306.

Amides react with NaN3 to give acyl azides in DMF at 25°C and produce symmetrical ureas in THF/H2O at 80 °C via a sequential acyl substitution and Curtius rearrangement. All acyl azides were also obtained from secondary amides via sequential reaction with p-toluenesulfonyl chloride and NaN3. In addition, keto-stabilized iminophosphoranes can also be prepared in a one-pot reaction.
D. Joseph, S. Lee, Org. Lett., 2022, 24, 6186-6191.