Boron azides in Staudinger oxidations and cycloadditions

Abstract

Staudinger reactions of Cy₂BN₃ with tri-substituted phosphines (R₃P) yielded the boron–nitrogen–phosphorus linked systems Cy₂BNPR₃ (R = Et, ^tBu, Cy, Ph) (1a–1d respectively). Similarly, reaction of (C₆F₅)₂BN₃ with the phosphines P^tBu₃, PPh₃, Ph₂PCCPh and Ph₂PCCPPh₂ yielded (C₆F₅)₂BNPR₃ (2a–d respectively). In contrast, the reaction of (C₆F₅)₂BN₃ with Ph₂P–CCp-tol in the presence of excess Me₃SiN₃ afforded the bicyclic product 3 [1-(C₆F₅)₂B-4-(p-tol)-1H-1,2,3-triazole-5-P(NH)Ph₂] 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-(C₆F₅)₂B-4-(P(O)OEt₂)-2H-1,2,3-triazole-5-P(O)(OEt)(OB(C₆F₅)₂)] is generated. The structures of 1b–d, 2b–d, 3 and 4 have been determined by X-ray diffraction.