Free-Radical-Mediated [2 + 2 + 1] Cycloaddition of Acetylenes, Amidines, and CO Leading to Five-Membered α,β-Unsaturated Lactams

Abstract

A free-radical-mediated [2 + 2 + 1] cycloaddition reaction comprising acetylenes, amidines, and CO was achieved by radical chain reaction to give five-membered α,β-unsaturated lactams in good yields. Both acyclic and cyclic amidines reacted with a variety of terminal acetylenes to afford monocyclic, bicyclic, and tricyclic lactams. We propose that vinyl radical carbonylation and nucleophilic addition of the amidine onto the resulting α-ketenyl radical give stable intermediates that are ready to undergo five-membered ring closure with elimination of tin radical.

Metal‐Free Radical [2+2+1] Carbocyclization of Benzene‐Linked 1,n‐Enynes: Dual C(sp3)H Functionalization Adjacent to a Heteroatom

“…[6][7][8]10] Initially,t he C(sp 3 )ÀH bond adjacent to the oxygen atom in 2a is broken to deliver the alkyl radical A by TBPB under heating (supported by the formation of 4a). [6][7][8]10] Initially,t he C(sp 3 )ÀH bond adjacent to the oxygen atom in 2a is broken to deliver the alkyl radical A by TBPB under heating (supported by the formation of 4a).…”

“…[4][5][6] However, the majority of such transformations focus on the use of CO as aone-carbon unit (the Pauson-Khand-type reaction). [4][5][6] However, the majority of such transformations focus on the use of CO as aone-carbon unit (the Pauson-Khand-type reaction).…”

Free‐Radical Multicomponent Processes

“…The latter may also exhibit electrophilic reactivity in specific cases, for instance, in tin-mediated cyclization of aza-enynes [72] or more recently in the [2 + 2 + 1]-cycloaddition process between acetylenic compounds, amidines, and CO (Scheme 14.24) [73]. In this three-component reaction, tributyltin radical adds onto the alkyne 110 to generate a vinyl radical that is trapped by CO to form the corresponding acyl radical I, which may be written as an α-ketenyl radical such as II.…”

Efficient Synthesis of Polycyclic γ‐Lactams by Catalytic Carbonylation of Ene‐Imines via Nickelacycle Intermediates

“…[1] TheP auson-Khand reaction is ar epresentative carbonylation which is mediated or catalyzed by transition metals and yields cyclic ketones. [3] The judicious choice of both the transition-metal catalyst and the reaction conditions is critical for generating these heterometalacycle intermediates in high efficiency under the catalytic carbonylation conditions. [3] The judicious choice of both the transition-metal catalyst and the reaction conditions is critical for generating these heterometalacycle intermediates in high efficiency under the catalytic carbonylation conditions.…”