Rsc_cc_c1cc13486h 1..3

In recent years, considerable effort has been devoted to develop methodologies which reduce multi-step transformations into one-step tandem processes. In this regard, the use of multifunctional catalysts, which promote sequential reaction steps without additional requirement of additives and/or co-catalysts, provides an effective way while taking care of two most basic challenges faced by a synthetic chemist, i.e. atom-economy and cost-reduction. The addition of N–H and C–H bonds across C–C p systems, also known as hydroamination and hydroalkylation, is one of the most interesting and intriguing subjects in synthetic organic chemistry, as they provide an attractive route for construction of a plethora of versatile building blocks. A variety of efficient catalytic systems have been developed for hydroamination of alkynes. However, hydroalkylation of alkynes is a relatively less studied area with most of the processes following an intramolecular pathway. Although the addition reaction of amines across the p system of terminal alkynes is studied in detail with various combinations of metal catalysts, interest in this area has been rejuvenated over the last half decade with some very interesting results (Scheme 1). Reaction of aniline with excess of alkyne has been reported to produce dihydroquinazoline over gold, silver and ruthenium catalysis (paths a and b, Scheme 1), where the reaction sequence involves hydroamination followed by cyclization via aromatic C–H activation. In a recent report, Corma and his co-workers have reported a gold(I) catalyzed intermolecular double-hydroamination of the anilines with terminal alkynes to obtain aryl bisenamines as unexpected products (path c, Scheme 1). Despite the numerous protocols for hydroamination and hydroalkylation of terminal alkynes available in the literature, to the best of our knowledge there is no report of any catalytic process where both the reaction steps occur concomitantly under the same reaction conditions. Previously, we have demonstrated that indium effectively activates terminal alkynes for cross coupling reaction as well as for nucleophilic addition. We report herein the first example of indium catalyzed tandem hydroamination and hydroalkylation of terminal alkynes with arylamines to generate a,b-unsaturated ketimines (path d, Scheme 1). Conjugated imines are versatile building blocks for construction of nitrogen heterocycles. Heterocycles such as pyrroles, pyrazoles, pyrimidines, pyridines, indolizines, quinolines and even a-amino acids and medium-sized carbocycles can be obtained by functionalization of these interesting subunits. As such, rapid and efficient approaches to the conjugated ketimines, especially under one-pot conditions are highly sought after because of their immense synthetic potential. In the present study, we show that indium effectively acts as a double catalyst for both hydroamination and hydroalkylation of terminal alkynes when reacted with arylamines. Preliminary studies were directed to investigate the catalytic action of indium trifluoromethanesulfonate on the hydroamination reaction of terminal alkynes with arylamines. Initially, reaction of p-toluidine with 1.1 equivalents of phenylacetylene was carried out. Formation of the desired imine by Markovnikov addition of