Ketomethylene compounds, attack

Ketomethylene, 4-(4-anilinobu tadienyli-dene), in the synthesis of tetra-methine neutrocyanines, 63 Ketomethylene compounds, attack on trimethine cyanines, 62 in synthesis of zeromethine cyanines,... 

The nucleophilic carbon of ketomethylene compounds can react with anhydrobases of different species in a basic medium. This reaction presents a narrow similitude with -CHj attack. The resulting dye, neut-rodimethine cyanine either mesomethyl-substituted or not. varies with the nature of the anhydro base (Scheme 30) (53. 54). 

As a consequence of the alternative distribution of an even number (2n) 7r electrons on an odd number (2n 1) carbon atoms, centers of the methine chain susceptible to nucleophilic attack are effectively the even carbons atoms starting from nitrogen, as it has been proven experimentally (103), particularly with a ketomethylene giving a neutrocyanine compound (53, 67). 

---