Formation of Allenyl Ketones, 3-Ethynylcoumarins, and Arylfurans, Furylfurans, and Furylthiophenes by Flash Vacuum Thermolysis of 3-Methylidenefuran-2(3H)-ones

Abstract

Flash vacuum thermolysis (FVT) of 3-methylidenefuran-2(3H)-ones 3 causes cheletropic extrusion of CO with formation of allenyl ketones 4. o-Chloro- and o-bromophenylmethylidenefuranones also afford allenyl ketones upon flash vacuum thermolysis, but in addition, 3-ethynylcoumarins 6 are formed via E/Z isomerization of the methylidenefuranones, cyclization, halogen atom migration, and HCl (HBr) elimination. The presence of strongly electron-withdrawing groups (nitroaryl or acetyl) on the acylallene moiety causes rearrangement to give 2-arylfurans 10 and 13 as well as 2-furylfurans and 2-furylthiophenes 16 by cyclization of the allenyl ketones. The reaction mechanisms are supported by calculations at the M06-2X/6-311+G(d,p) level of theory.

V-Shaped Bis-Coumarins: Synthesis and Optical Properties

“…Interestingly, the oxapyrenone skeleton has been found in the metabolites of various orchids and lichens − and recently the first total synthesis of santiagonamine, isolated from stems and branches of the South American shrub Berberis darwinii, was reported . Regardless of their presence in nature , and their well-documented biological activity, − the growing interest in the synthesis of new coumarins has mainly been driven by their applications to photonics. − As a result of their strong light absorption, , high fluorescence quantum yield, and large Stokes shift, − coumarins have been widely investigated as optical brighteners, as fluorescent probes, , as emitter layers in organic light emitting diodes (OLEDs), , and as photosensitizers in organic solar cells , and they have also been successfully incorporated into energy- and electron-transfer arrays. − An increasing number of possible applications has accelerated recent progress in coumarin synthesis. , …”

Chemo‐selective Synthesis of 4‐Chloro‐3‐(arylethynyl)coumarins and their Synthetic Transformations

“…[5] A few synthetic methods are known for the preparation of 3-(arylethynyl)coumarins (Scheme 1). Some of these methods involve Sonogashira coupling (Scheme 1a), [6] CÀ H activation (Scheme 1b), [7] flash vacuum thermolysis (Scheme 1c), [8] and visible light induced on/off method (Scheme 1d), [9] etc. for the synthesis of 3-(arylethynyl)coumarin derivatives.…”

Photophysics of Derivatives of 3-Hydroxybenzo[c]coumarin

“…Coumarins are well-known heterocycles, which have been extensively explored for various photonic applications, − including use as fluorescence probes, , optical brighteners, and as emitter layers in organic light emitting diodes (OLEDs). , They have also been successfully incorporated into energy- and electron-transfer arrays , and have served as initiators in two-photon polymerization . Because of their importance, many synthetic strategies have been developed for the preparation of coumarins. − Although the first π-expanded coumarins were synthesized by Pechmann in 1884, it was not until recently that this field started to burgeon. Numerous new types of π-expanded coumarins have been synthesized in the past decade. − Ahn and co-workers recently revealed the superb optical properties of benzo­[ g ]­coumarins and employed them in fluorescence imaging. , Although coumarins have attracted attention for 100 years, , their optical properties are still puzzling the researchers .…”