The Catellani reaction enables an ortho-C-H activation based on oxidative addition of Pd(0) and an intermediary carbopalladation of norbornene. Among its variants, the recently developed C2-selective alkylation of indoles is particular as it employs Pd(ii) as the source of palladium. This review describes the mechanistic background of this transformation. Applications in total synthesis and in the synthesis of biologically relevant molecules are illustrated and further developments of the method are discussed.
Employing 1,3-dibromopropane, 1,4-dibromobutane, and 1,5-dibromopentane as biselectrophiles, the annulation of indoles was probed in the presence of PdCl2(MeCN)2 as a catalyst and norbornene as a transpositional ligand. Ring formation to a five-membered ring was observed at positions C2 and N, while annulation of a six-membered ring occurred at positions C2 and C3. The latter cascade process was successfully applied to the direct synthesis of 1,2,3,4-tetrahydrocarbazoles from indoles (11 examples, 31–68% yield). Seven-membered-ring annulation was feasible by an initial coupling at positon C2 followed by alkylation at C3.
Bei der Umsetzung von Harnstoff mit Phosphorpentachlorid entsteht unter Chlorwasserstoffentwicklung (Cl3PN)2CO. Außerdem treten POCl3, Cl2P(O)NCO, Cl3PNCN und weitere PNC‐Verbindungen als Nebenprodukte auf. Die gleichen Produkte entstehen auch bei der Reaktion von H2NCONHP(O)Cl2 und (Me3SiNH)2CO mit Phosphorpentachlorid. Es gelang, solche Reaktionsbedingungen zu ermitteln, bei denen das Reaktionsprodukt einen maximalen Anteil von (Cl3PN)2CO enthält. (Cl3PN)2CO zersetzt sich beim Erhitzen unter Bildung von POCl3 und dem vermutlich trimeren Trichlorphosphazencyan.
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