Highly Efficient Synthesis of Multisubstituted Furans through Cupric Halide-Mediated Intramolecular Halocyclization of 1-(1-Alkynyl)cyclopropyl Ketones

Access to functionalized alkynylcyclopropanes via reductive radical-polar crossover-based reactions of 1,3-enynes with alkyl radicals

Herein, using a single-electron-transfer reduction-based radical-polar crossover process as a strategy, protocols dealing with the preparation of functionalized alkynylcyclopropanes have been successfully developed via the reactions of 1,3-enynes with alkyl radicals. In addition to redox-neutral photocatalysis, nickel catalysis with zinc as the reductant is also an alternative to enable reactions of 1,3-enynes with redox-active N-hydroxyphthalimide esters. The synthetic application of alkynylcyclopropane has also been demonstrated.

Crystal structure of 3-allyl-4-(2-bromoethyl)-5-(4-methoxyphenyl)-2-(p-tolyl)furan, C23H23BrO2

C23H23BrO2, monoclinic, P21/c (no. 14), a = 24.193(4) Å, b = 5.8614(10) Å, c = 13.873(3) Å, β = 93.168(3)∘, V = 1964.3(6) Å3, Z = 4, R gt (F) = 0.0316, wR ref (F 2) = 0.0915, T = 296(2) K.

Crystal structure of 3-allyl-4-(2-bromoethyl)-5-(4-methoxyphenyl)-2-phenylfuran, C22H21BrO2

C21H21BrO2, monoclinic, P21/c (no. 14), a = 22.175(2) Å, b = 5.8375(6) Å, c = 14.8729(14) Å, β = 100.936(1)°, V = 1890.3(3) Å3, Z = 4, R gt (F) = 0.0343, wR ref(F 2) = 0.0839, T = 296(2) K.

Direct synthesis of highly functionalized furans from donor-acceptor cyclopropanes via DBU-mediated ring expansion reactions

A DBU-mediated, unprecedented formal ring expansion reaction of 2-acyl-3-arylcyclopropane-1,1-dicarbonitriles for the synthesis of multisubstituted furan derivatives is reported. This transformation represents the regioselective ring-opening reaction of cyclopropane-1,1-dicarbonitriles and annulation using an intramolecular addition cascade reaction protocol for the synthesis of fully substituted furans includes use of readily available starting materials, mild reaction conditions, and it is transition-metal catalyst free, has good functional tolerance, and broad substrate scope.