Photochemical Radical Cation Cycloadditions of Aryl Vinyl Ethers

Abstract

Radical cation cycloadditions have long been known as unique reactions and yet are intensively studied chemical transformations in the field of modern synthetic organic chemistry. The key to developing new reactions of this class is the generation and control of highly reactive radical cation intermediates. Herein, we report TiO2 photochemical [2+2] and [4+2] cycloadditions using aryl vinyl ethers as radical cation precursors. The constructions of various four‐ and six‐membered rings are made possible by these radical cation cycloadditions. Although detailed mechanistic aspects remain unclear, 2,3‐dimethyl‐1,3‐butadiene (3) is found to be more radicalophilic than 2‐ethyl‐1‐butene (2) and effectively traps the radical cation of the aryl vinyl ethers to construct six‐membered rings.

Ag3PO4 enables the generation of long-lived radical cations for visible light-driven [2 + 2] and [4 + 2] pericyclic reactions

“…3d). Okada et al used a substantial excess of TiO 2 (e.g., > 6 equiv) to minimize the accumulated electron per NP and extra LiClO 4 (1.0 M) to stabilize the radical cations 18,22,23,[25][26][27] . In contrast, Ag 3 PO 4 photocatalysis can harvest the visible spectrum of sunlight and achieve a high yield of the desired product without any additives.…”

“…From a practical standpoint, they are generally considered stable, recyclable, inexpensive, and environmentally friendly, making them an ideal choice for use in photosynthesis 25 . However, the efficiency of isPCs in the 1e-oxidative activation of non-polar and noncoordinative C = C moieties on their surfaces is typically low 17,20,[26][27][28][29][30][31][32][33] . One obstacle is the short lifetime of holes (fs to ns 34 ), which significantly slows down the 1e-oxidation of the C = C moieties (Fig.…”

Ag3PO4 Nanoparticles Enable the Generation of Long-lived Radical Cations for Visible Light-Driven [2+2] and [4+2] Pericyclic Reactions

“…Okada et al used a substantial excess of TiO 2 (e.g., > 6 eq) to minimize the accumulated electron per NP and extra LiClO 4 (1.0 M) to stabilize the radical cations. 18,[22][23][25][26][27] In contrast, Ag 3 PO 4 photocatalysis can harvest the visible spectrum of sunlight and achieve a high yield of the desired product without any additives.…”

“…However, the e ciency of isPCs in the 1eoxidative activation of non-polar and non-coordinative C=C moieties on their surfaces is typically low. 16,19,20,[24][25][26][27][28][29][30][31] One obstacle is the extremely short lifetime of holes (fs to ns 32 ), which signi cantly slows down the 1e-oxidation of the C=C moieties (Figure 1a). Moreover, even if some alkene radical cations are slowly generated at the surfaces of a traditional isPC like TiO 2 , they undergo few intermolecular C-C formation reactions.…”

Arene C–H Amination with N-Heteroarenes by Catalytic DDQ Photocatalysis

“…Photocatalytic DDQH 2 reoxidation is a promising option for DDQ photocatalytic chemistry, and such a dual photocatalytic system, composed of the photocatalyst for DDQH 2 reoxidation and DDQ itself, can maximize the photo energy to contribute to sustainable organic synthesis. We have been developing TiO 2 photocatalytic reactions that are promoted by initial SET oxidation. − While TiO 2 absorbs ultraviolet (UV) light, DDQ is excited by the same light source . We questioned whether TiO 2 photocatalysis has the potential to reactivate DDQH 2 to DDQ (Scheme ).…”