| Abstract
| - The Staudinger reaction of azides has now been followedby NMR and other spectroscopic techniques.syn-(Azidomethyl,methyl)(methyl,methyl)bimane(1) and Ph3P form a triazaphosphadieneintermediate 2 and then the bimaneP-triphenyliminophosphorane 3. Theiminophosphorane reactswith an acyl chloride to yield an iminophosphonium salt 4which then forms the oxazaphosphetane13. The latter undergoes an electrocyclic reversion toform the phosphine oxide and the chloroimines7E and 7Z, the last beinghydrolyzed to the (acylamido)bimane 6. This set ofreactions constitutesthe “iminophosphorane pathway”. A significant diversion of thereaction path to an (N-alkylamino)phosphonium chloride 8 occurs through reaction of4 with H2O present in the CDCl3 andthroughreaction of 3 with HCl. A different azide(α-azido-o-xylene 1b) produces the(acylamido)-o-xyleneas the sole product. A less sterically hindered phosphine(tri-2-furylphosphine) reacts more slowlyto form the iminophosphorane 3a from the azidobimane1. Reaction of the bimaneP-tri-2-furyliminophosphorane with acyl chloride gives only the(acylamido)bimane 6. If the acylchlorideis mixed with 1, followed by addition of thePh3P, the triazaphosphadiene adduct 5 is formedviathe triazaphosphadiene. The adduct 5 is convertedrapidly into a six-membered cyclic compound11. The latter either loses nitrogen to yield6 via 7Z and 7Eand the phosphine oxide or loseschloride 10 through a novel chloride-induced eliminationreaction from its protonated form. Thechange in procedure thus results in a dramatic change in the reactionpathway, a reaction set thatconstitutes the “triazaphosphadiene adduct pathway”. In thecase of α-azido-o-xylene, α-chloro-o-xylene (10b) is the only product. Thereactions of the azides 1 or 1b withtri-2-furylphosphinealso produce chlorides as the major products accompanied by someacetamido derivatives. Thenucleophile-induced reaction explains a “surprising result”(formation of ester rather than amide)reported by Sahlberg et al. (Sahlberg, C.; Jackson, A. M.; Claesson, A.Acta Chem. Scand. 1988,B42, 556−562). The intramolecular “aza-Wittig”reaction may depend on the nucleophilicity ofthe triazaphosphadiene. A comprehensive mechanistic scheme for theStaudinger reaction of azidesis conveniently divided into the following: (A) formation of thetriazaphosphadiene (Scheme 1),(B) reactions of the triazaphosphadiene (Scheme ), and (C) reactionsvia the iminophosphorane(Scheme 3). Some approximate kinetic parameters are reported forsome of the reactions.
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