Лако-красочные материалы — производство

Several syntheses of the diketopyrrolopyrrole skeleton have been described in the lit­erature. In the following sections, different syntheses published are summarized.

11.2.1

Reformatsky Route

In the original publication [1] describing the first DPP synthesis (Scheme 11.1) via a Reformatsky reaction, the authors postulated that the formation of the DPP 2 proceed via an oxidative dimerisation as depicted in Scheme 11.2.

In 1988, new investigations on the Reformatsky route were published [5]. Synthe­sis of crucial intermediates and crossing experiments using two different benzoni — triles strongly indicated that the reaction did not proceed via an oxidative dimeri­zation mechanism and the intermediate 4B. Instead a new mechanism was postu­lated, involving a sequential build up of the DPP chromophore via the pyrrolinone ester 6A as the crucial intermediate (Scheme 11.3).

The first step is considered to involve the condensation of the Reformatsky reagent with benzonitrile to yield the Zn salt 3B. C-alkylation by bromoacetate, followed by ring closure, is believed to lead to the hitherto elusive key intermedi­ate 6A, a pyrrolinone ester. Condensation with a second molecule of benzonitrile and subsequent cyclization of intermediate 7, which could be isolated and was also mentioned by Farnum, finally affords the DPP 2.

11.2.2