Nitrene Transfer Reaction in Pd Coordination Sphere

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Azidoformate reacts with allylic ethers to give the <alpha> -imines specifically under catalyzed by Pd( <II> ). Mchanistic studies revealed the followings:1) The same <alpha> -imines were formed almost quantitatively by non-catalyzed reaction of azide and the corresponding vinylic ethers. 2) Isomerization of an allylic ether to the corresponding vinylic ether was much slower than the above <alpha> -imine formation even in the presence of Pd( <II> ).3) Rates of the <alpha> -imine formation were found to be first order each in the ether and in the azide.4) Other unsaturated ethers such as homoallylic ethers also afforded to the <alpha> -imine by the catalyzed reaction with the azide. These ethers, however, isomerized to the corresponding allylic ethers under the reaction conditions.5) Easiness of <alpha> -imine formation decreased as the following order; methanesulfonyl azide azido-formate phenyl azide stannyl azide. These results suggest the following mechanism: Isomerization of the allylic ether to the vinylic ether is promoted by the new Pd( <II> ) complex formed by exchanging the ligand PhCN to the azide molecule. The vinylic ether reacts with the azide to give <alpha> -imine via 1,3-dipolar addition followed by heterolysis of the triazine, involving with nitrogen evolution and 1,2-shift of hydrogen or alkyl groups.Reaction of allylic sulfides with azidoformate did not give <alpha> -imines, but the products derived from ylide formation between sulfide and nitrene, even in the presence of Pd( <II> ).