A facile one-pot domino reaction for the stereoselective synthesis of acryl derivatives promoted by Ca(OTf) 2 Srinivasarao Yaragorla a,⇑ , Pyare Lal Saini a , Abhishek Pareek a , Abdulrahman I. Almansour b , Natarajan Arumugam b a Organic & Medicinal Chemistry Laboratory, Department of Chemistry, Central University of Rajasthan, Bandarsindri, NH-8, Ajmer, Rajasthan 305817, India b Department of Chemistry, College of Science, King Saud University, PO Box 2455, Riyadh 11451, Saudi Arabia article info Article history: Received 12 January 2016 Revised 23 March 2016 Accepted 27 March 2016 Available online xxxx Keywords: b-Enamino ester Indolyl acrylates Oxindolyl acrylates Domino reactions Heterocyclic compounds Calcium catalysis abstract A facile one-pot domino reaction for the stereoselective synthesis of acryl derivatives has been reported using alkaline earth catalyst [Ca(OTf) 2 ]. Initially aryl amine reacts with ethyl propiolate to form b-enamino ester which further reacts with aryl aldehyde and indole in the presence of Ca(OTf) 2 to give indolyl acrylates. It is interesting to note that in the absence of indole the reaction leads to the formation of benzylidene bisacrylates. Similarly b-enamino ester reacts with another electrophilic partner isatin in the presence of Ca(OTf) 2 to give oxindolyl acrylates. The products were isolated in good yields by simple filtration. Ó 2016 Elsevier Ltd. All rights reserved. Multicomponent reactions and domino reactions provide a sus- tainable and diversity oriented synthesis of novel heterocyclic molecules in one-pot. 1 In addition they offer atom economy and step economy synthesis, domino reactions are also treated as eco- friendly reactions because they minimize the usage of large amounts of organic solvents which are used to purify the interme- diates in each step through column chromatography. 1 On the other hand, the active intermediate b-enamino ester which results from the addition of primary amines to electron deficient alkynes is known as a key building block for the synthesis of various hetero- cycles and pharmaceutical compounds. 2,3 Several domino reac- tions were developed to trap the b-enamino ester with a wide variety of electrophiles and nucleophiles in a sequence to generate the novel nitrogen containing heterocyclic scaffolds. 4–10 When we looked into the literature there are very few reports available for the synthesis of indolyl acrylates (5), oxindolyl acrylates (8), and benzylidene (6) bisacrylates from the active b-enamino ester. 11,12 Yan et al. reported an efficient FeCl 3 catalyzed domino synthesis of indolyl acrylates at rt with moderate yields and the reaction took 30 h for completion. 11 Later the same group reported the syn- thesis of arylidene bisacrylates and oxindolyl acrylates using FeCl 3 as the catalyst. 12 Albeit the elegant methods available for the synthesis of indolyl acrylates, oxindolyl acrylates, and arylidene bisacrylates, it is highly desirable to develop an alternative cat- alytic system (non-transition metal catalyst) to reduce the reaction time and enhance the product yields. In continuation of our research aimed toward the novel synthesis of heterocyclic mole- cules using alkaline earth catalysts (as an alternative to transition metal catalysts) 13 herein we report a Ca(OTf) 2 catalyzed domino reaction for the synthesis of indolyl acrylates, oxindolyl acrylates, and arylidene bisacrylates. Initially we planned to study the synthesis of indolyl acrylates which involves the four component domino reaction of aniline, ethyl propiolate, aryl aldehyde, and indole. Literature studies illus- trate that there are two stages in the reaction. First stage aniline and ethyl propiolate react at rt in ethanol to give active b-enamino ester, but the second stage requires activation (in the form of a cat- alyst) to trap the b-enamino ester with suitable electrophilic reagents. We commenced our synthesis by reacting stoichiometric amounts of aniline and ethyl propiolate in ethanol at rt and observed the formation of b-enamino ester after 12 h; the stoichio- metric amounts of benzaldehyde and indole were added to the above reaction mixture along with 5 mol % of Ca(OTf) 2 and 5 mol % Bu 4 NPF 6 (additive) and continuously stirred at rt for 12 more http://dx.doi.org/10.1016/j.tetlet.2016.03.098 0040-4039/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +91 463 238535; fax: +91 463 238722. E-mail address: Srinivasarao@curaj.ac.in (S. Yaragorla). Tetrahedron Letters xxx (2016) xxx–xxx Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet Please cite this article in press as: Yaragorla, S.; et al. Tetrahedron Lett. (2016), http://dx.doi.org/10.1016/j.tetlet.2016.03.098