Donor−acceptor cyclopropanes are widely used in organic synthesis owing to their ability to react as synthetic equivalents of 1,3-zwitterions. Recently, reactions of donor−acceptor cyclopropanes where they exhibit other reactivity types have also been studied intensely.
As part of the ongoing research by the scientistss of the laboratory № 6 of the Zelinsky Institute on the reactivity of donor-acceptor cyclopropanes, a method was developed for the usage of a bicyclopropyl system activated by the incorporation of donor and acceptor groups as a synthetic equivalent of 1,6-zwitterions in the presence of Lewis acids. The use of the GaI3 + Bu4N+GaI4– system leads to the formation of products of the formal addition of HI to the bicyclopropyl system. Carrying out the reaction of the activated bicyclopropyl system with terminal alkynes in the presence of GaCl3 or GaBr3 as a Lewis acid makes it possible to obtain acyclic 7-chloro(bromo)-hepta-2,6-dienylmalonates. The reaction of the bicyclopropyl system with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) catalyzed by Yb(OTf)3 is also accompanied by the opening of both cyclopropane rings, while one PTAD molecule leads to the formation of the annulated tetrahydropyridazine ring, and the second one is incorporated in the malonyl fragment.
Konstantin V. Potapov, Dmitry A. Denisov, Valeriia V. Glushkova, Roman A. Novikov, Yury V. Tomilov Donor−Acceptor Bicyclopropyls as 1,6-Zwitterionic Intermediates: Synthesis and Reactions with 4‑Phenyl-1,2,4-triazoline-3,5-dione and Terminal Acetylenes J. Org. Chem. 2020, 85, 23, 15562–15576. DOI: 10.1021/acs.joc.0c02293.