A New Synthesis of Push-Pull Pyrroles, Their Oxidation to Stable 3H-Pyrroles and an Unexpected Anellation Reaction

A new synthesis of push-pull pyrroles of type 5 was developed starting from bis(imidoyl chlorides) I and various iminodiacetic acid derivatives 3. The use of appropriate N-trifluoroacetyl residues as protecting/activating group proved to be the method of choice for the straightforward preparation of the 3,4-diarylamino-1H-pyrroles 5. When benzothiazole substructures are present in 2,5-position of heterocycles 5, a two-electron oxidation leads to 3H-pyrroles of type 6 in excellent yields. However, in the case of cyano or ester groups, a further oxidative process immediately led to the new 3H-pyrrolo[3,4-b]quinoxalines 7 via intramolecular ring anellation. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)