Photochromism of o-Nitrophenyl-Substituted Oxazabicycles

Investigation of Triangle Terthiophene and Hydroxyphenylbenzothiazole Configured Fluorescent Dye with a Triple Bond Bridge

A photochromic dye was constructed by incorporation of a carbon-carbon triple bond spaced triangle terthiophene skeleton and hydroxyphenylbenzothiazole. Regular photochromic behavior was investigated with alternated UV (254 nm) and visible light (≥ 400 nm) irradiation. The color of dye in solution can be cycled between pink and colorless. Additionally, the dye solution strongly fluoresces in THF with the absolute quantum yield (QY) being 0.56. When irradiation with 254 nm light, the emissive solution can be effectively quenched to photo-stationary sate (Φ = 0.05). An emission "on-off" cycle could be established based on the UV/visible light irradiation cycle. The photochromic dye also exhibits good photo- and thermal-stability at room temperature. The emission decay profile indicates typical single component character with the fluorescence lifetime being 6.68 ns. The emission color was determined by the CIE 1931 coordinates of x = 0.14, y = 0.25 in the blue region.

Regiodivergent Synthesis of Bis(4-oxycoumarin)-based Dioxabicycles: Exploration of [4 + 4] (Heterocyclo)reversion/addition and 1,5-Hydrogen Shift Photochromism

Two isomeric dioxabicyclic molecular skeletons were constructed by employing the concepts of divergent synthesis. A base-mediated and an acid-catalyzed pseudo-three-component reaction of two equivalents of 4-hydroxycoumarin and (Z)-3-chloro-3-phenylacrylaldehyde yielded the corresponding bis(4-oxycoumarin)-based 2,6- and 2,8-dioxabicycles, respectively. The prepared colorless 2,6-dioxabicycles turned red upon UV irradiation and underwent the reverse reaction when exposed to visible light. The photochromism was proposed to proceed via a sequential [4 + 4] (heterocyclo)addition/reversion and 1,5-hydrogen shift on the basis of photogenerated product-trapping experiments.

Light/inductive effect induced isomerization of chromeno-5-methyl-2,6,9-trioxabicyclo[3.3.1]nonadienes

An efficient rearrangement of coumarin-based trioxabicycles and the effect of UV light and electron-withdrawing substituents on this transformation are reported.

One-Pot Construction of 1-Phenylchromeno[3,4- b]pyrrol-4(3 H)-one: Application to Total Synthesis of Ningalin B and a Pyrrolocoumarin-Based Electrochromic Switch

An efficient construction of 1-phenylchromeno[3,4- b]pyrrol-4(3 H)-one via coupling of 1-styrylpyrrolidine and 4-chloro-3-nitrocoumarin as a key step is reported. This reaction is further applied to the total synthesis of the natural product ningalin B in five linear steps with an overall yield of 41.5% and a pyrrolocoumarin-based electrochromic switch.

Multicomponent synthesis of pyrano[2,3-c]coumarins

A base-catalyzed, pseudo-four-component reaction of 4-hydroxycoumarin, two molecules of acetone, and amine towards the synthesis of pyrano[2,3-c]coumarins is reported. The mechanism of this multicomponent reaction is proposed. The reaction is further extended to the preparation of coumarin-substituted pyrano[2,3-c]coumarins by a base-catalyzed, pseudo four-component reaction of two molecules of 4-hydroxycoumarin and two molecules of acetone.

A base-catalyzed, pseudo-four-component reaction of 4-hydroxycoumarin, two molecules of acetone, and amine towards the synthesis of pyrano[2,3-c]coumarins is reported.

Catalyst-free one-pot domino reactions for selective synthesis of functionalized 2,8-oxazabicyclo[3.3.1]-nonanes and 5H-indeno[1,2-b]pyridin-5-ones

A simple and efficient method for one-pot selective synthesis of functionalized 2,8-oxazaxabicyclo[3.3.1]nonanes and hydroxy-containing 5H-indeno[1,2-b]pyridin-5-ones under catalyst-free conditions has been developed.