High pressure thermal and the photosensitized dimerizations of 2-pyrones

Pressure effects on the radical–radical recombination reaction of photochromic bridged imidazole dimers

“…High pressure effects on chemical reactions are essential to understand the behaviour of biological functions and the origin of life in the deep sea. This has inspired many researchers and the pressure effects on the various chemical reactions and photochemical properties have been reported, such as cycloadditions, [1][2][3][4][5] Z-E isomerizations, [6][7][8][9] intermolecular interactions, [10][11][12] asymmetric photoreactions, 13,14 photochromic reactions [15][16][17][18][19] and so on. [20][21][22] Since the effects of pressure on chemical reaction rates are generally correlated with the difference in the partial molar volumes between the reactant and the transition state, these studies have revealed that not only enthalpy but also entropy are important factors to control chemical reactions.…”

tert-Butyl(2-oxo-2H-pyran-5-yl)carbamate as the First Chameleon Diene Bearing an Electron-Donating Substituent

“…The ready formation of a dimer during the cycloadditions of pyrones is precedented. Unsubstituted 2( H )pyran-2-one is reported to undergo dimerization under photochemical and high-pressure conditions [ 62 , 63 , 64 ]. To the best of our knowledge, however, this is the first example of the dimerization of pyrones under thermal conditions.…”

Inverse‐Electron‐Demand Diels–Alder Reactions of 2‐Pyrones: Bridged Lactones and Beyond

“…Therefore, 2‐pyrone can react with both electron‐rich and electron‐poor dienophiles, making them ambiphilic. However, the cycloaddition of unsubstituted 2‐pyrone is usually plagued by self‐polymerization under thermal conditions [5] . Fortunately, substituted 2‐pyrones are suitable for DA reactions, and the electronic property of the substituent on the pyrone ring decides which type of DA reaction happens.…”

“…However, the cycloaddition of unsubstituted 2-pyronei su sually plagued by self-polymerization under thermalc onditions. [5] Fortunately, substituted 2-pyrones are suitable for DA reactions, and the electronic property of the substituent on the pyrone ring decides which type of DA reactionh appens.I th as been recognized that electron-rich 2-pyrones are good dienes for NEDDA reactions. On the other hand, electron-poor 2-pyrones participate in IEDDAr eactions as electrophilic dienes with higher reactivity because the electron-withdrawingg roup on the pyrone ring destroys the internal electron delocalization (less aromaticity) and lowerst he LUMO level.I ts hould be noted that bromo-and dibromo-substituted 2-pyrones can carry out both NEDDA reactions and IEDDA reactions flexibly (Scheme 2).…”