Pyrroles electron deficient unsaturated compounds

TABLE 7.10. 2-(TRIFLUOROMETHYL)PYRROLES FROM REACTION OF 5(2/7)-OXAZOLONES WITH ELECTRON-DEFICIENT UNSATURATED COMPOUNDS... 

A useful reaction for the synthesis of unsaturated seven-membered heterocycles is the (2 + 2)-cycloaddition of heteroaromatic compounds, e.g., 1 //-pyrrole, furan, or thiophene derivatives, with acetylenes. In combination with a subsequent intramolecular (2 + 2)-cycloreversion (Section IV,B,2) of the annulated cyclobutene moiety, ring enlargement with two carbon atoms can be achieved. 1-Heterocycloheptatrienes, such as benzol6]azepines,26,27,65,66 benzo[fc]oxepins,67,68 benzo[6]-thiepins,69,70 and thiepins,18,71 have been successfully prepared in this way other routes are either nonexistent or laborious.72 In these compounds the reacting carbon-carbon double bond constitutes part of a (4n + 2)7r-electron system and in the (2 + 2)-cycloaddition the resonance energy of the aromatic nucleus is lost. Just like the nonaromatic heterocycles, heteroaromatic compounds have been reported to undergo (2 + 2)-cycloaddition reactions both with electron-deficient and with electron-rich acetylenes. 

Firouzabadi, H., Iranpoor, N. and Nowrouzi, E, The facile and efficient Michael addition of indoles and pyrrole to a,/ -unsaturated electron-deficient compounds catalyzed by aluminium dodecyl sulfate trihydrate [A1(Ds)3] 3H2 0 in water, Chem. Commun., 2005, 789-791. 

Other acids have also been explored. For instance, a heleropoly acid catalyzed Friedel-Crafts alkylation of indole and pyrrole with enones and electron-deficient olefins in water at room temperature, affording good yields at 0.3mol% catalyst loading [112]. Similarly, a carbon-based solid add was shown to catalyze effidendy the reaction of indoles with a,p-unsaturated carbonyl compounds in water, and the... 

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