Co-Catalyzed C(sp³)–C(sp²) bond cleavageviahydrogen atom transfer

Abstract

The discovery of a new Co-catalyzed hydrogen atom transfer (HAT) C(sp3)-C(sp2) bond cleavage method to access ketones from alkenes is reported. This unprecedented transformation features mild reaction conditions and good...

Total Synthesis of Vilmoraconitine

“…With tricyclic alkene 7 in hand, the stage was set for investigating the key hydrodealkenylative fragmentation (Scheme ). Pleasingly, subjection of 7 to the slightly modified conditions (O 3 , MeOH, −78 °C; FeSO 4 ·7H 2 O, 4-methoxy­benzenethiol, −78 to 23 °C) based on Kwon’s report resulted in the generation of the expected aldehyde product 6 in 77% yield on a gram scale. , Of note, this method proved to be suitable for complex substrates, in which an unprotected ketone carbonyl group was compatible. Next, TFA-promoted Mannich cyclization of aldehyde 6 occurred efficiently to give the tetracyclic product 5 (90% yield).…”

“…The tetracycle 5 would be established through a Mannich cyclization of aldehyde 6 , which, notably, would enable simultaneous formation of the B/E/F rings in a single-step fashion. At this stage, 6 could be accessed by a hydrodealkenylative fragmentation from alkene 7 based on a method developed by the Kwon group, although application of this protocol to the total synthesis of complex natural products has not been reported. In turn, 7 could be readily prepared via fragment coupling of the known aldehyde 8 and bromide 9 , followed by an oxidative dearomatization/Diels–Alder cycloaddition (OD/DA) cascade …”

Aerobic C–C Bond Cleavage of Allylic Alcohols via Co-Catalyzed Hydrogen Atom Transfer

“…In the past few decades, metal hydride hydrogen atom transfer (MHAT) reactions have attracted more attention due to their high chemoselectivity and regioselectivity in alkene functionalization chemistry . The formation of C–C bonds via the HAT process has been well established, whereas the cleavage of C–C bonds was rare until Qin et al recently disclosed the first HAT-mediated C­(sp 3 )–C­(sp 2 ) bond cleavage of alkenes to access ketones . With respect to allylic alcohol substrates, tandem radical addition/1,2-aryl migrations were observed previously .…”

“…This alkyl radical reacted with O 2 to yield Co III –alkylperoxo species IV . Then the O–O bond could be cleaved to generate alkoxy radical V and the Co III –O• radical . At this stage, the Co III –O• radical would abstract the H atom of the hydroxyl group, which led to the formation of an unstable adjacent glycol-type diradical intermediate.…”