Nitrosoarenes Implement Cascade Cyclization of 1-Allenyl-2-alkynylbenzenes through Diradical Mechanism

Abstract

This work reports cascade cyclization between 1allenyl-2-alkynylbenzenes and nitrosoarenes. When these two components reacted alone under N 2 , N,O-functionalized indanefused isoxazolidines 3 were obtained selectively. DFT calculations verify that this reaction sequence involves unprecedented nitrone/ alkyne cycloadditions, followed by diradical rearrangement.

Aerobic oxidation/metal-free cyclization cascades of nitrosoarenes and allenynes with TEMPO/O2: a switch of diradical to single radical intermediates

“…We employed DFT calculations 13 to elucidate the reaction mechanism (Scheme 6). From our prior studies, 9,10 a long-lived initial diradical A , arising from reactants 1a and 2a , is observable via EPR spectroscopy. Notably, the formation of this diradical is exothermic with Δ H = −10.9 kcal mol −1 .…”

“…Compound 3a′ was produced from the cascade cyclizations of reactants 1a and 2a . 10 To increase the yield of our target 3a , we altered the operation procedure through a slow addition of 1a to a mixture of TEMPO and nitrosobenzene in DCE. In this case, the yield of compound 3a was increased to 23% whereas compound 3a′ was completely absent (entry 2).…”

“…9 When 1-allenyl-2-alkynylbenzenes are studied with the same nitrosoarenes, metal-free cascade annulations occur to afford highly N , O -functionalized indane-fused isoxazolidines efficiently, featuring the first success of diradical-mediated cascade cyclizations (eqn (3)). 10 This work explores the new utility of such metal-free nitroso reactions, through a switch of diradical to single radical intermediates. As shown in eqn (4), the persistent TEMPO radical 1 b is used to intercept long-lived diradical intermediates II , forming new single radicals to enable the uptake of oxygen, ultimately affording substituted 1-indanones 3 and 4 fused with an aziridine ring.…”

Three-Component Synthesis of Di-Keto Aziridines and Highly Functionalized Alkenes from Sulfoxonium Ylides, Nitrosoarenes, and Alkynes

“…Based on the above experimental results and previous literature studies, ,, a possible mechanism for the catalyst-free three-component reaction is proposed in Scheme . Initially, benzoyl sulfoxonium ylide 1a reacts smoothly with nitrosobenzene 2a to produce nitrone intermediate 7a via a transition state Ts1 and with the extrusion of DMSO.…”