Regio- and chemoselective synthesis of nitrogen-containing heterocycles via the oxidative cascade cyclization of unactivated 1,n-enynes

Abstract

The development of a method for performing radical initiated intramolecular cascade cyclization of 1,n-enynes provided a competent protocol for producing structurally diverse complex heterocycles.

Metal-Free Domino Oligocyclization Reactions of Enynals and Enynones with Molecular Oxygen

“…The same cycloisomerization through two different catalytic systems (iodine and gold) enabled the formation of the same product that has been reported by Liang (Scheme b). Also, cyclopropanation of 1,6-enynes using Pd­(OAc) 2 as a catalyst and acetate ion as an oxygen source has been demonstrated by Sanford et al Wang et al developed a radical cascade cyclization reaction of 1,6-enynes that achieved the same aza[3.1.0]­bicycles using TBHP as an oxidant and oxygen source (Scheme c) . After careful deliberation, we noticed that all previous examples involved metal-catalyzed condition or oxidizing reagents .…”

Difunctionalization of Dienes, Enynes and Related Compounds via Sequential Radical Addition and Cyclization Reactions

“…An iodine radical-initiated reaction for the synthesis of difunctionalized N -heterocyclic compounds was reported by the Wang group in 2020. The reactions of 1,6- or 1,7-enynes, TBHP and I 2 in CH 3 CN gave compound 21 in moderate-to-good yields ( Scheme 20 ) [ 33 ]. The reaction mechanism suggests that iodide radical, generated from the reaction of I 2 with TBHP, adds to the C≡C triple bond of enyne followed by 6- exo cyclization to yield tertiary radical M-29 .…”

Cycloisomerization of enynones by aluminum halides: construction of bicyclo[3.1.0]hexanes by introducing halides

“…Other known approaches toward bicyclo[3.1.0]hexanes from enynes include the methods triggered by the oxidative addition of Pd to propargylic esters or vinyl halides, 5 by the insertion of alkynes into metal–carbon or metal–heteroatom bonds, 6 by the formation of metallacycles 7 or carbenes, 8 and by metathesis with metal carbene complexes, 9 in addition to radical cyclization. 10 Nevertheless, the method with the introduction of halogens is limited to the TiCl 4 -mediated cycloisomerization of O -acetyl enynols (Scheme 1b), 2 i although there are some methods using substrates such as alkene-tethered ynals, 8 h , i ynones, 8 j ynoates 6 e – g ,7 g ,8 j and ynamides. 2 f ,6 e , f ,8 j…”