Photocatalytic Decarboxylative [3 + 2] and [4 + 2] Annulation of Enynals and γ,σ-Unsaturated N-(Acyloxy)phthalimides by NaI/PPh₃ Catalysis

Abstract

A practical and eco-friendly strategy for the radical-mediated decarboxylative [3 + 2] and [4 + 2] annulation of enynals and γ,σ-unsaturated N-(acyloxy)­phthalimides through the photoactivation of an electron donor–acceptor (EDA) complex has been developed. A wide range of primary, secondary, and tertiary alkyl N-hydroxyphthalimide (NHP) esters can be used as suitable substrates for the synthesis of fused ketones without any transition-metal catalysts or oxidants. This protocol features a broad substrate scope, excellent selectivity, and clean reaction conditions.

Formal total synthesis of macarpine via a Au(I)-catalyzed 6-endo-dig cycloisomerization strategy

“…Ketone 5 was prepared in a four-step procedure. Firstly, a Sonogashira coupling between 6-bromopiperonal ( 2 ) and trimethylsilylacetylene was performed to furnish aldehyde 3 [ 17 – 18 ] in 89% yield. A following nucleophilic addition reaction of aldehyde 3 by methylmagnesium bromide (MeMgBr) gave alcohol 4 in 99% yield, which was oxidized by pyridinium chlorochromate (PCC) leading to the formation of ketone compound and the deprotection of the silyl group was accomplished in the presence of potassium carbonate (K 2 CO 3 ) and methanol to provide the terminal alkyne 5 in 96% yield in two steps.…”

Radical annulation using a radical reagent as a two-carbon unit

“…Equally within the visible light system, in 2021, Li's group studied γ,σ-unsaturated N -(acyloxy)phthalimides to form electron donor–acceptor (EDA) complexes, which then underwent decarboxylative [4 + 2] annulation with enynals to synthesize fused ketones (Scheme 18). 31 In this method, the inexpensive and readily available NaI/PPh 3 system was utilized to avoid using any transition-metal catalysts or oxidants, with selectivity and environmental friendliness. Simultaneously, based on the previous studies and control experiments, a possible mechanism is proposed in Scheme 18.…”

Synthesis of quinazoline by decarboxylation of 2-aminobenzylamine and α-keto acid under visible light catalysis

“…Visible light, a clean, environmentally friendly, and sustainable energy source with high atomic efficiency, has attracted increasing attention from researchers. 13 Visible-light photocatalysis has been demonstrated to realize redox catalysis through a single-electron transfer process under very mild conditions. 14 In 2016, Tang et al 15 synthesized quinazoline directly through amide by using visible light mediated C(sp 3 )–C(sp 2 ) bond formation.…”