Pyrrole 2.4- diacyl

No significant amounts of diacylated products are obtained under Vilsmeier-Haack conditions an indirect method for preparing pyrrole-2,5-dicarbaldehydes is outlined in Scheme 16 (78S295, 82CJC383). 

Perfluoroalkanoyl chlorides and anhydrides are also acylating agents Tri-fluoroacetic anhydride acylates a number of pyrroles, thiophenes, and furans without a catalyst [37, 38, 39] AzuUne can be diacylated without a catalyst in 12 h [40] (equation 26). 

Intermolecular examples of pyrroles serving as 2jr components in cycloadditions are rare but examples include A-tosyl-2- and -3-nitropyrrole and A-tosyl-2,4-diacyl-pyrroles," however in an intramolecular sense tricyclic 6-azaindoles are produced where the 4jr component is a 1,2,4-triazine (29.2.1). "... 

Similarly, heating of methyl 3-acyl-l-(diphenylmethyleneamino)-4,5-dioxo-4,5-dihydro-l//-pyrrole-2-carboxylates 96 gave the corresponding dimethyl 2,8-diacyl-3,9-dioxo-5,5,ll,ll-tetraphenyl-3,5,9,lTtetrahydrodipyrazolo[l,2- 7 l, 2 -i [l,2,4,5]tetrazine-l,7-dicarboxylates 99 in good yields. The proposed mechanism involves thermal decarbon-ylation to give the ketene intermediate 97, which cyclizes into the azomethine imine 98, followed by dimerization (Scheme 24) <2004T5319>. 

The iminium salt products from Vilsmeier reactions, before hydrolysis, can be neatly utilised for further Friedel-Crafts substitution. The substituent is strongly meta directing, thus leading to 2,4-diacylated pyrroles, and also serves to protect the potential aldehyde. ... 

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