Navigating Visible‐Light‐Triggered (aza and thia) Paternò‐Büchi Reactions for the Synthesis of Heterocycles

Abstract

Harnessing visible light to trigger (aza and thia) Paternò‐Büchi reaction injects new vitality into [2+2] photocyclization reaction and enable impressive reactivity modes. The popular (aza and thia) Paternò‐Büchi reaction is one of the most efficient ways to synthesize strained four‐membered heterocycles. Recently, visible‐light‐triggered (aza and thia) Paternò‐Büchi reactions have received considerable attentions as this strategy has overcome some long‐standing challenges, and remarkable achievements have been made within this field. Strained four‐membered heterocyclics with favorable properties provide a perfect combination of stable skeletons for pharmaceutical chemistry and raction intermediates for further transformation. In this review, we highlight the most recent advances in visible‐light‐triggered (aza and thia) Paternò‐Büchi reaction with an emphasis on reaction mechanism and applications. Organization of the review follows a subdivision according to reaction type and substrate classes.

Visible photons as ideal reagents for the activation of coloured organic compounds

“…The achievements in visible-light photocatalysis in the last few decades have also brought traditional photochemical processes into focus, including Paternò–Büchi cycloadditions. 89–92 However, the visible-light mediated, photocatalyst-free synthesis of oxetanes has only been sparsely reported in the literature. Benzyls ( 6.1a and b , Scheme 6), which exhibit a weak absorption in the visible region (400–450 nm), were successfully employed in both regio- and stereoselective [2+2] cycloaddition with simple olefins ( e.g.…”

Sustainable Synthesis through Catalyst‐Free Photoinduced Cascaded Bond Formation

“…[40] Thia-Paternò-Büchi reaction is a prominent classic photochemical reaction used to synthesize various S-containing heterocycles. [41] In 2020, Aitken and co-workers reported a solvent concentration-dependent cascade reaction to synthesize tetrahydrothiophenes 13 d or thietane 13 c from thiobenzophenone 13 a and alkene moiety 13 b under irradiation of an Hg lamp (Scheme 13). [42] When a lower concentration of cyclohexane solvent i. e., 25 mM was used selectively tetrahydrothiophenes product 13 d was formed, whereas in the case of a higher concentration of the solvent i. e., 130 or 260 mM thietane 13 c was formed.…”

Regioselective Diels–Alder Reactions of Anthracenes with Olefins via Visible Light Photocatalysis in a Homogeneous Solution

“…For 9-substituted anthracenes, the poor regioselectivities of [4 + 2] photocycloadditions provide mixtures containing head-to-head and head-to-tail mutual orientation except for some intramolecular examples . In the past decades, visible-light sensitization has been successfully applied for photocycloadditions of aryl olefins, enones, 1,3-dienes, and even heteroaromatics . Particularly, Iwasawa and co-workers used a constrained host–guest system to realize the [4 + 2] photocycloaddition of anthracene derivatives with several dienes and alkenes under visible light irradiation .…”