Visible-Light-Induced Dehydrohalogenative Coupling for Intramolecular α-Alkenylation: A Way to Build Seven- and Eight-Membered Rings

Abstract

Scheme 1. Overview of C(sp 2 )−C(sp 2 ) Coupling Reactions Letter pubs.acs.org/OrgLett

Visible Light‐Induced Synthesis of Functionalized Coumarins

“…Very recently, Guo's group reported the synthesis of seven‐membered ring bearing coumarin adducts 163 from 4‐(4‐bromobut‐3‐ene‐1‐yl)oxycoumarins 162 via an energy transfer process (Scheme 46). [83] Here, thioxanthone (TX) worked as a photocatalyst and MeCN as a solvent. Despite narrow substrates scope, this protocol opened a potential route for the synthesis of seven‐membered ring bearing coumarin adducts in excellent yields.…”

Multi‐Photocatalyst Cascades: Merging Singlet Oxygen Photooxygenations with Photoredox Catalysis for the Synthesis of Alkaloid Frameworks

“…Despite the well-established advantages of cascade reactions (in whatever form they take;d omino,t andem or telescoped sequences), [11] photocascades have remained underdeveloped. [12] Photocascades have been limited to the use of just one photocatalyst; thereby,restricting the range of reactions that can be included in the cascade,a sw ell as,t he series in which they can be employed. There are examples of multiple oxidative or reductive quenches,o r, more,r arely mixed redox or energy/ electron transfer steps;b ut, as ingle photocatalyst is always employed.…”

“…There are examples of multiple oxidative or reductive quenches,o r, more,r arely mixed redox or energy/ electron transfer steps;b ut, as ingle photocatalyst is always employed. [12] Then on-productive energy and electron transfer between photocatalysts (inter-catalyst quenching) is thought to present an insurmountable hurdle to the use of multiple catalysts within the same cascade sequence.D ual catalysis,i ncluding one photocatalytic step,h as been recorded; [12a, 13, 14] however,t he second catalytic entity brings something else to the transformation (such as,u se of an organocatalyst to induce enantioselectivity alongside the photochemical process [13,14] ). In the investigations described herein, we provide two solutions to this conundrum.…”

Visible Light-Induced Pericyclic Cascade Reaction for the Synthesis of Quinolinone Derivatives with an Oxabicyclo[4.2.0]octene Skeleton

“…Developing tandem reactions on the ground of these transformations is rewarding. Recently, we reported a cascade reaction that undergoes [2 + 2]-photocycloaddition, hydrogen halide elimination, and retro-4π-electrocyclization to construct seven-or eight-membered rings under visible light catalysis (Scheme c) . In the investigation of the construction of the eight-membered ring, a rearrangement product with an oxabicyclo[4.2.0]­octene skeleton was found after extended reaction time.…”

“… a A solution of 1a (0.1 mmol), thioxanthone (10 mol %), and base in anhydrous solvent (10 mL) was irradiated by 30 W violet LEDs (410–420 nm) at rt under argon atmosphere for 12 h. b Yields were determined by 1 H NMR analysis of the crude reaction mixture using CH 2 Br 2 (0.1 mmol) as internal standard. c A solution of 1a (0.1 mmol), thioxanthone (5 mol %), and NaOMe (0.12 mmol) in anhydrous MeCN (10 mL) was irradiated by 5 W violet LEDs (390–410 nm) at rt under argon atmosphere for 4 h. d Yield of 2a , ref . e Some unidentified byproducts were formed. f Isolated yield of 3a . g 5 mol % of thioxanthone was applied. h The reaction was carried out under exclusion of light. i No thioxanthone was applied. …”