Nitrene Transfer Reaction in Pd Coordination Sphere

叠氮甲酸酯在Pd（<II>）催化下与烯丙醚反应生成< α > -亚胺。机理研究表明：1)叠氮化物与相应的乙烯醚的非催化反应几乎可以定量地生成相同的< α > -亚胺。2)即使在Pd（<II>）存在的情况下，烯丙基醚到乙烯基醚的异构化也比上述< α > -亚胺的形成慢得多。3)在醚和叠氮化物中< α > -亚胺的生成速率均为一级。4)其他不饱和醚如均烯醚也通过与叠氮化物的催化反应生成< α > -亚胺。然而，这些醚在反应条件下异构化成相应的烯丙基醚。5) < α > -亚胺生成难易程度依次递减；甲磺酰叠氮化物-叠氮甲酸苯基叠氮化物-锡基叠氮化物。这些结果表明：通过配体PhCN与叠氮化物分子交换形成新的Pd（<II>）配合物，促进了烯丙基醚向乙烯基醚的异构化。乙烯醚与叠氮化物通过1,3-偶极加成反应生成< α > -亚胺，然后三氮杂解，涉及氮的析出和氢或烷基的1,2移位。烯丙基硫化物与叠氮甲酸酯反应不会生成< α > -亚胺，但即使在Pd（<II>）存在的情况下，硫化物与亚胺之间也会生成ylide。

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> ).