Microwave-accelerated conjugate addition of 2-arylindoles to substituted β-nitrostyrenes in the presence of ammonium trifluoroacetate: an efficient approach for the synthesis of a novel class of CB1 cannabinoid receptor allosteric modulators

2-Arylindoles, in general exhibit reduced reactivity towards the conjugate addition to substituted nitrostyrenes, when compared to indoles. We report here an efficient, expeditious and high-yielding conjugate addition of 2-arylindoles to substituted β-nitrostyrenes in the presence of ammonium trifluoroacetate under microwave irradiation. This method is mild with high and reproducible yields and is selective for addition of β-nitrostyrenes when compared to other electrophiles. The results obtained from the optimized microwave method consistently provided improved yields in a shorter time compared to those of the conventional heating synthetic route.