Lewis Acid-Enabled Chemodivergent Cycloadditions of Donor-Acceptor Cyclopropanes with Indoline-2-Thiones
Chen-Ying Zhai1, Bing Zhao2, Xue-Long Wang1
1Key Laboratory of Green Chemistry of Sichuan Institutes of Higher Education, College of Chemistry and Environmental Engineering, Sichuan University of Science & Engineering, Zigong 643000, China.
Abstract:
Lewis acid-enabled reactions of donor-acceptor cyclopropanes (DACs) with indoline-2-thiones are reported. The reaction exhibits tunable annulation depending on the Lewis acid and the substituent at N1 of the indoline-2-thiones. With AlCl3 as the Lewis acid and 1-isopropylindoline-2-thiones as reactants, a direct ring opening with DACs, followed by intramolecular nucleophilic addition/dehydration takes place leading to the formation of dihydro-2H-thiepino[2,3-b]indoles in moderate to good yields. Using Yb(OTf)3 as promoter and 1-unsubstituted indoline-2-thiones as reactants, a (3 + 2) cycloaddition with DACs accompanied by sulfur rearrangement nucleophilic addition/dehydration takes place to give 3-indolyl-4,5-dihydrothiophenes in moderate yields. In addition, the synthetic transformation of 3-indolyl-4,5-dihydrothiophene to sulfone and indole-based axially chiral scaffolds further extends the synthetic utility and structural complexity.
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