Synthesis of DMSS from Diketene Methyl 4-Chloroacetoacetate

Synthesis of DMSS from Diketene (Methyl 4-Chloroacetoacetate) 

DMSS 7 undergoes facile acid catalyzed condensations with aniline and other primary aromatic amines to form 2,5-diarylamino-3,6-dihydroterephthalates 12 in excellent yields [10] and the respective structures have been confirmed by various analytical techniques including IR and NMR spectroscopy [llj. 

The reaction is probably initiated by thermal elimination of methanol by the high process temperatures (250-300 °C) to form an intermediate ketene 13, which cyclizes rapidly to the intermediate acridone 14. Transformation to a second ketene 15 by elimination of methanol followed by cyclization forms the dihydroquinacridone 16. 

Kinetic studies of the cyclization reaction confirm that a two-stage sequential mechanism is involved and a comparison of the activation energies of each demonstrates that the reaction rate of the initial ring closure is approximately three times that for the second [8B, 13A]. The insoluble 6,13-dihydroquinacridone 16 is 

The oxidation of 16 to quinacridone can be accomplished by several methods including reaction with aromatic nitro compounds in the presence of base in aqueous alcohol solvents [13], by interaction with dioxygen (introduced by air injection) [14] or by contact with hydrogen peroxide [15]. Also, dehydrogenation can be accomplished by interaction with various quinones such as anthraquinone-2-sulfonic acid [16] or by contact with suitable catalysts such as palladium-charcoal [17]. Successful oxidation is exemplified by the production of chemically and crys-tallographically pure quinacridone products. 

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