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

Abstract

A novel metal-free direct addition of molecular oxygen to the C–C triple bond toward benzannulated oxygen-bridged seven-membered ring systems and aza[3.1.0]­bicycle skeletons under 3O2 atmosphere has been described. The reaction proceeds through at least three intramolecular C–O and C–C bond forming steps via green, simple, and unprecedented domino radical processes with high selectivity and good yields.

Transition metal catalysed cascade C–C and C–O bond forming events of alkynes

“…Here, when R 1 = H, 12a reacted intramolecularly to give cyclopropane-opened intermediate Int-12i, which upon intramolecular cyclization afforded 12b (Scheme 12). 34 The enantioselective intramolecular carboalkoxylation of alkyne-tethered aryl ethers 13a for the synthesis of enantiomerically enriched indanones 13b was reported by Lai and coworkers (Scheme 13). 35 They used several chiral cyclometalated oxazoline Au(III)-complexes to achieve a better ee.…”

“…Here, when R 1 = H, 12a reacted intramolecularly to give cyclopropane-opened intermediate Int-12i , which upon intramolecular cyclization afforded 12b (Scheme 12). 34…”

Base-Promoted Intramolecular Addition of Vinyl Cyclopropanecarboxamides to Access Conformationally Restricted Aza[3.1.0]bicycles

“…A literature review indicates that the metal-mediated cyclopropanation domino reaction of chain enynes is the most commonly used strategy for the construction of aza [3.1.0]bicycle derivatives in terms of scalability and substrate scope, which highly rely on the in situ-generated metal carbene species in the presence of Pd, Au, Ru, Co, Ni, and Rh salts as catalysts [20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Occasionally, the same conversion starting from enyne analogues has also been achieved by a photocatalytic pathway [34][35][36] as well as metal-free organocatalytic processes [37][38][39][40][41][42], mechanisms that are similar to the metal carbene A literature review indicates that the metal-mediated cyclopropanation domino reaction of chain enynes is the most commonly used strategy for the construction of aza [3.1.0]bicycle derivatives in terms of scalability and substrate scope, which highly rely on the in situgenerated metal carbene species in the presence of Pd, Au, Ru, Co, Ni, and Rh salts as catalysts [20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Occasionally, the same conversion starting from enyne analogues has also been achieved by a photocatalytic pathway [34]…”

“…Occasionally, the same conversion starting from enyne analogues has also been achieved by a photocatalytic pathway [34][35][36] as well as metal-free organocatalytic processes [37][38][39][40][41][42], mechanisms that are similar to the metal carbene A literature review indicates that the metal-mediated cyclopropanation domino reaction of chain enynes is the most commonly used strategy for the construction of aza [3.1.0]bicycle derivatives in terms of scalability and substrate scope, which highly rely on the in situgenerated metal carbene species in the presence of Pd, Au, Ru, Co, Ni, and Rh salts as catalysts [20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Occasionally, the same conversion starting from enyne analogues has also been achieved by a photocatalytic pathway [34][35][36] as well as metal-free organocatalytic processes [37][38][39][40][41][42], mechanisms that are similar to the metal carbene processes (Scheme 1a). Another two effective approaches for the synthesis of 3-azabicyclo[3.1.0]hexanes involve the derivatization reactions of substituted cyclopropanes, such as C(sp 3 )-H bond activated alkenylation/amination tandem reactions and intramolecular aminolysis reactions Molecules 2023, 28, 3691 2 of 15 (Scheme 1b) [43][44][45][46][47]…”