Boron azides in Staudinger oxidations and cycloadditions

摘要

Staudinger reactions of Cy_2BN_3 with tri-substituted phosphines (R_3P) yielded the boron-nitrogen-phosphorus linked systems Cy_2BNPR_3 (R = Et, tBu, Cy, Ph) (1a-1d respectively). Similarly, reaction of (C_6F_5) _2BN_3 with the phosphines P~tBu_3, PPh_3, Ph_2PCCPh and Ph_2PCCPPh_2 yielded (C_6F_5)_2BNPR_3 (2a-d respectively). In contrast, the reaction of (C_6F_5) _2BN_3 with Ph_2P-CCp-tol in the presence of excess Me_3SiN_3 afforded the bicyclic product 3 [1-(C _6F_5)_2B-4-(p-tol)-1H-1,2,3-triazole-5-P(NH) Ph_2] in which both a Staudinger and a cycloaddition reaction has taken place. However, if the Staudinger reaction is prohibited via phosphine oxidation as in the case of (EtO)_2P(O)CCP(O)(OEt)_2 then the unusual dimeric product 4 [2-(C_6F_5) _2B-4-(P(O)OEt_2)-2H-1,2,3-triazole-5-P(O)(OEt)(OB(C _6F_5)_2)] is generated. The structures of 1b-d, 2b-d, 3 and 4 have been determined by X-ray diffraction.