Sulfur-Mediated Synthesis of Indole-Fused Medium-Sized Rings
Yiwen Huang1, Chuang Lu1, Shilin Wang1
1Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, China.
Abstract:
We disclose herein a transition-metal-free strategy to synthesize indole-fused medium-sized rings directly from parent indole molecules in one pot. The reaction design involves an interrupted Pummerer reaction between indoles and activated cyclic sulfoxides, followed by ring opening of the resulting sulfonium acetals, and finally cyclization. With trifluoroacetic anhydride (TFAA)-activated sulfoxides of five-membered N,S-acetals, indole-fused seven-membered rings were constructed with the sulfur atom attached to position C-2 of the indole rings; on the other hand, with the TFAA-activated sulfoxide of a six-membered S,S-acetal, the widely available 1,3-dithiane, indole-fused eight-membered rings were obtained with the sulfur atom attached to position C-3 of indoles.
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