An atmosphere and light tuned highly diastereoselective synthesis of cyclobuta/penta[b]indoles from aniline-tethered alkylidenecyclopropanes with alkynes

Abstract

Metal-free and environmentally friendly synthesis highly controlled by natural sources like visible light and air (or oxygen) is always a pursuit of green chemistry. In this paper, an atmosphere and light tuned highly diastereoselective synthesis of two important polyheterocyclic skeletons: cyclobuta/penta[b]indoles from aniline-tethered alkylidenecyclopropanes with alkynes, has been developed. The chiral cyclobuta/penta[b]indoles have also been obtained by optical resolution.

The Construction of Molecular Complexity from Functionalized Alkylidenecyclopropanes (FACPs)

“…Reactionofa niline-tethered alkylidenecyclopropanes with extern alkynes. [23] Chem.E ur.J. 2019, 25,7591 -7606 www.chemeurj.org tronic and steric effects of the adjacent substituents (Scheme 22 a).…”

“…More recently, we have also reported a metal‐free and atmosphere‐ and light‐tuned highly diastereoselective synthesis of cyclobuta/penta[ b ]indoles from aniline‐tethered alkylidenecyclopropanes with extern alkynes. Products 73 were obtained without a ring‐opening process under argon atmosphere in good to excellent yields, whereas products 74 were obtained under oxygen atmosphere and household light (Scheme a) . A proposed mechanism is outlined in Scheme b.…”

“…Recent examples of thermal-induced reactions of allene-type FACPs. Chem [23] Ap roposed mechanism is outlined in Scheme 17 b. Initial [2+ +2] cycloaddition occurredt og enerate intermediate 75,followed by intramolecular nucleophilica ttack of the anilinem oiety to the Michael acceptorc yclobutene, delivering products 73.T he 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO)-trapped experiment showed that the transformation of 73 to 74 was fully inhibited, which revealed that the formation of 74 probablyw ent through ar adical process.…”

Construction of Carbocycles from Methylenecyclopropanes

“…[71] In the same year, Huang reported the Lewis acidcatalyzed reactiono fV CPs 141 with aromatic aldehydest op roduce benzo [c]fluorene derivatives 142 in good yields [Eq. (63)]. [72] Ther eactionp roceeded throughc ascade electrophilic addition of aldehydes to 141,c leavage of the distal bond of the CP moiety,f ol-lowed by two successive intramolecular Friedel-Crafts reactions teps.S imilarly,S n(OTf) 2 -o r BF 3 .…”

“…(54)]. [63] Notably, the reactionw as promoted by household light, which is ag reene nergy source from the sustainable chemistry viewpoint. In the process,aspiro[2.3]hexane skeleton was initially formed, which then rearrangedi nto 126 via aS ET-initiatedf ree radical reaction.…”