11 октября, 2015 
Pokraskin A second new route to DPP Pigments was developed and published in 1983 [5, 6]. In this route, a succinic ester is condensed in a pseudo-Stobbe condensation with an aromatic nitrile in the presence of strong base to afford the desired DPP in good yield (Scheme 11.4). Mechanistically, the formation of a DPP unit from succinic esters is believed to proceed along the pathway shown in Scheme 11.4. The initially formed enaminoester 5B cyclizes to the pyrrolinone ester 6B, which further reacts under basic conditions with another molecule of benzonitrile. Subsequent ring closure affords the DPP 2.
Very recently, a solvent-free variation of the succinic ester route under microwave assistance has been described [7].
11.2.3
Succinic Amide Route
Yet another synthesis has been described by Gompper [8], involving the reaction of succinamide with N, N-dimethylbenzamide diethylacetal (Scheme 11.5).
11.2.4
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