4^th European Chemistry Congress

Biography

Biography: Eric Pasquinet

Abstract

The aza-Wittig reaction is a widely known and used reaction, which consists of the coupling between an iminophosphorane (obtained from the reaction of a trialkylphosphine on an azide) and an unsaturated carbonyl-type compound. In its intramolecular version, the aza-Wittig reaction gives access to many aza-heterocycles from 5- to 7-membered rings. In such processes, the use of N-electrophiles has never been reported. We investigated nitroso compounds as electrophiles to promote the formation of a N=N double bond. In particular, we found that  minophosphoranes (coming from the reaction between an aromatic azide and a trialkylphosphine) could cyclize onto an ortho benzylic nitroso moiety, leading to a 3H-indazole that isomerized into its more stable 1H analogue. This process can be operated one-pot, without isolation of the intermediate iminophosphorane. This means that, in a single operation starting from an aromatic azide, the targeted 1H-indazole is generated. Various aryl- and hetaryl azides were used to demonstrate the generality of the method, leading to 1H-indazoles, 1H-benzoindazoles and 1H-azaindazoles. The reaction pathway will also be discussed. It involves a mechanism analogous to that reported for the aza-Wittig reaction.  Therefore the key transformation of the process was given the name ‘diaza-Wittig’.