Boron Trifluoride Mediated Ring-Opening Reactions of trans-2-Aryl-3-nitro-cyclopropane-1,1-dicarboxylates. Synthesis of Aroylmethylidene Malonates as Potential Building Blocks for Heterocycles
摘要:
trans-2-Aryl-3-nitro-cyclopropane-1,1-dicarboxylates, upon treatment with BF3 center dot OEt2, undergo ring-opening rearrangement and the Nef reaction to give aroylmethylidene malonates. The products are found to be potential precursors for heterocycles, such as imidazoles, quinoxalines, and benzo[1,4]thiazines.
A two-step synthesis of 2,3-disubstituted thiophenes from trans-2-aryl-3-nitrocyclopropane-1,1-dicarboxylates and 1,4-dithiane-2,5-diol is described. The nitrocyclopropane dicarboxylates when treated with boron trifluoride etherate formed aroylmethylidene malonates in situ through ring-opening followed by rearrangement and a Nef reaction, and subsequent addition of 1,4-dithiane-2,5-diol and triethylamine
Highly enantioselective Friedel–Crafts C2-alkylation reactions of 3-substituted indoles with α,β-unsaturated esters and nitroalkenes were developed using chiral Lewis acids as catalysts, which afforded chiral indole derivatives bearing C2-benzylic stereogenic centers in good to excellent yields (up to 99%) and enantioselectivities (up to 96% ee).