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Synthesis of Unsymmetrical Pyrrolo[3,2-b]pyrrole-2,5-diones. -Unsymmetrically disubstituted oxalic acid-bis(imidoyl) dichlorides such as (IV) are prepared for the first time. They are used in a one-pot synthesis of pyrrolopyrroles (VI). Additionally, the synthesis of a 2,2'-bisquinazolinone (VIII) is demonstrated. -(LANGER*, P.; HELMHOLZ, F.; SCHROEDER, R.; Synlett 2003, 15, 2389-2391; Inst. Chem.

Synthesis of Unsymmetrical Pyrrolo[3,2-b]pyrrole-2,5-diones S y n t h e s i s o f U n s y m m e t r i c a l P y r r o l o [ 3 , 2 -b ] p y r r o l e -2 , 5 -d i o n e s Abstract: The first unsymmetrical oxalic acid-bis(imidoyl)dichlorides were prepared and applied to the one-pot synthesis of the first unsymmetrical pyrrolo[3,2-b]pyrrole-2,5-diones and 2,2¢-bisquinazolin-4-ones.

Unsymmetrical oxalic acid-bis(imidoyl)dichlorides were prepared from ethyl 2-chloro-2-oxoacetate in three steps.

Unsymmetrical pyrrolo[3,2-b]pyrrole-2,5-diones and bis(quinazolin-4-on-2-yls) were prepared by one-pot cyclisations of unsymmetrical oxaldi(arylimidoyl) dichlorides.Pyrrolo [3,4-c]pyrrole-1,4-diones A, studied in detail by Gompper and coworkers, 1 are of considerable relevance in the field of material sciences and have been used as key building blocks of photo-and electroluminescent conjugated polymers D and dendritic structures. 2 The isomeric pyrrolo[3,2-b]pyrrole-2,5-diones C represent promising pigment dyes 3 and can be regarded as aza-analogues of pulvinic dilactones B (Figure 1). The parent pulvinic acids represent natural pigments isolated from lichens and fungi. 4 Pyrrolo[3,2-b]pyrrole-2,5-diones exhibit pigment properties and a number of syntheses of symmetrical derivatives have been reported. 5,6 This includes, for example, a three-step synthesis starting with (N-phenylacetyl)acetic acid amino ester 5a or a one-step approach using pulvinic acid (autoclave reaction, 140-180 °C). 5b In the course of our program directed to the development of new cyclisation reactions 7 of oxalic acid bis(imidoyl) dichlorides, 8 we have reported a versatile approach to symmetrical pyrrolo[3,2-b]pyrrole-2,5-diones by one-pot cyclisation ('double-anion-capture reaction') of ester enolates with oxaldi(imidoyl) dichlorides. 9 Recently, we have extended our methodology and reported the first synthesis of unsymmetrical oxalic acid bis(imidoyl) dichlorides. 10 These new and important building blocks were successfully employed to the synthesis of unsymmetrical pyrrolo[3,2-b]pyrrole-2,5-diones. 10a Herein, we report full details of this study. In addition, we report the synthesis of unsymmetrical bis(quinazolin-4-on-2-yls) 11 based on 'double-anion-capture reactions' of methyl 2-aminobenzoate with oxaldi(imidoyl) dichlorides.The reaction of ethyl 2-chloro-2-oxoacetate with a number of anilines 1 gave the known 12 ethyl 2-oxo-2-(arylamino)acetates 2 (Scheme 1). The reaction of 2 with a variety of anilines afforded the unsymmetrical oxalamides 3a-j (42-83%). Reflux of a toluene solution of oxalamides 3 with phosphorus pentachloride furnished, after recrystallisation from n-heptane, the unsymmetrical oxalic acid bis(imidoyl) dichlorides 4a-j (23-77%). The lithium diisopropylamide mediated reaction of bis(imidoyl) dichlorides 4 with various ethyl arylacetates 5 gave the unsymmetrical pyrrolo[3,2-b]pyrrole-2,5-diones 6a-u (Table 1). For all products, acceptable yields were obtained, except for 6u. Pyrrolo[3,2-b]pyrrole-2,5-diones 6 exhibit a low solubility in organic solvents which is, in fact, an important feature of pigment dyes. The products were recrystallised from dimethyl sulfoxide or N,N-dimethylformamide. The 13 C NMR measurements required long acquisition times.All pyrrolo[3,2-b]pyrrole-2,5-diones 6 represent orangecoloured pigment dyes. Similar to the symmetrical derivatives, 9 the UV-Vis absorptions were mainly influenced by the aryl groups attached to the carbon atoms of the pyrrolo[3,2-b]pyrrole-2,5-dione core structure. ...