Nitrene Transfer Reaction in Pd Coordination Sphere

在钯催化下，叠氮甲酸酯与烯丙基醚反应，专一性地生成了<alpha>-亚胺<II>。机理研究表明：1）<alpha>叠氮化合物与相应的乙烯基醚在非催化条件下几乎定量地生成相同的亚胺。2)烯丙基醚异构化为相应的乙烯基醚比上述-亚胺的形成慢得多<alpha>，即使在Pd（）的存在下<II>。3）<alpha>-亚胺的形成在醚和叠氮化物中均为一级反应。4）其它不饱和醚如高烯丙基醚也<alpha>通过与叠氮化物的催化反应生成-亚胺。这些醚，然而，异构化为相应的烯丙基醚的反应条件下。5）<alpha>-亚胺的形成的容易程度下降，为以下顺序：甲磺酰基叠氮叠氮基甲酸苯叠氮甲锡酰叠氮。这些结果表明，以下机制：烯丙基醚的异构化的乙烯基醚的促进由新的Pd（<II>）络合物通过交换配体PhCN的叠氮分子形成。烯丙基硫醚与叠氮<alpha>基甲酸酯的反应不生成-亚胺<alpha>，但在Pd（Ⅱ）存在下，硫醚与氮烯形成叶立德，生成-亚胺<II>。

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> ).