NO₃ chemistry of wildfire emissions: a kinetic study of the gas-phase reactions of furans with the NO₃ radical

Furans are emitted to the atmosphere during biomass burning from the pyrolysis of cellulose. They are one of the major contributing VOC classes to OH and NO3 reactivity in biomass burning plumes. The major removal process of furans from the atmosphere at night is reaction with the nitrate radical, NO3. Here we report a series of relative rate experiments in the 7300 L indoor simulation chamber at CNRS-ICARE, Orléans, using a number of different reference compounds to determine NO3 reaction rate coefficients for four furans, two furanones, and pyrrole. In the case of the two furanones, this is the first time that NO3 rate coefficients have been reported. The recommended values (cm3 molecule−1 s−1) are: furan (1.50 ± 0.23) × 10−12, 2-methylfuran (2.37 ± 0.55) × 10−11, 2,5-dimethylfuran (1.10 ± 0.33) × 10−10, furan-2-aldehyde (9.28 ± 2.3) × 10−14, 5-methyl-2(3H)-furanone (3.00 ± 0.45) × 10−12, 2(5H)-furanone < 1.410−16, and pyrrole (7.35 ± 2.06) × 10−11. The furan-2-aldehyde + NO3 reaction rate is found to be an order of magnitude lower than previously reported. We also recommend a faster rate for the α-terpinene+NO3 reaction ((2.70 ± 0.81) × 10−10 cm3 s−1). These experiments show that for furan, alkyl substituted furans, 5-methyl-2(3H)-furanone, and pyrrole, reaction with NO3 will be the dominant removal process at night, and may also contribute during the day. For 2(5H)-furanone, reaction with NO3 is not an important atmospheric sink.

IntraMolecular Diels–Alder Reactions of Vinylarenes and Alkynyl Arenes (the IMDAV Reaction)

This comprehensive review summarizes the published literature data concerning the intramolecular Diels–Alder reactions of vinylarenes (the IMDAV reaction) and alkynyl arenes from 1970 to 2019, and covers mainly intramolecular [4+2] cycloaddition reactions of vinyl- or acetylene-substituted furans, thiophenes, pyrroles, indoles, imidazoles, benzenes, and naphthalenes, in which the unsaturated substituent is linked directly to an arene moiety. The selected area of the Diels–Alder reaction differs from other forms of [4+2] cycloadditions due to the uniqueness of the diene fragment, which, along with an exocyclic multiple bond, includes the double bond of an aromatic or heteroaromatic nucleus in its system. Thus, during the formation of the [4+2] cycloaddition intermediate, the aromaticity of furan, thiophene and even benzene rings is broken, leading, as a rule, to the formation of heterocyclic structures rarely accessible by other methods, in contrast to the majority of intermolecular Diels–Alder reactions, with the highest degree of chemo-, regio-, and diastereoselectivity. Therefore, the IMDAV approach is often used for the synthesis of naturally occurring and bioactive molecules, which are also discussed in this review alongside other applications of this reaction. Whenever possible, we have tried to avoid examples of radical, photochemical, oxidative, precious-metal-complex-catalyzed cyclizations and other types of formal [4+2] cycloadditions, focusing on thermal Diels–Alder reactions in the first step, according to the classical mechanism. The second stage of the process, aromatization, is unique for many initial substrates, and hence considerable attention in this overview is given to the detailed description of the reaction mechanisms.1 Introduction2 IMDAV Reactions of Vinylfurans2.1 Alkenes as Internal Dienophiles2.2 Alkynes and Allenes as Internal Dienophiles3 IMDAV Reactions of Vinylthiophenes3.1 Alkenes as Internal Dienophiles3.2 Alkynes as Internal Dienophiles4 IMDAV Reactions of Vinylbenzothiophenes5 IMDAV Reactions of Vinylpyrroles6 IMDAV Reactions of Vinylindoles6.1 Alkenes as Internal Dienophiles6.2 Alkynes as Internal Dienophiles7 IMDAV Reactions of Styrenes and Vinylnaphthalenes7.1 Alkenes as Internal Dienophiles7.2 Alkynes as Internal Dienophiles7.3 Alkynes as Internal Dienophiles in Aryl Acetylenes (the Intramolecular Dehydro Diels–Alder Reaction)8 IMDAV Reactions of Vinylimidazoles, Vinylisoxazoles and Vinylpyridines9 Conclusion10 Abbreviations

Photocatalytic Synthesis of Tetra-Substituted Furans Promoted by Carbon Dioxide

We report a simple protocol for the transition metal-free, visible-light-driven conversion of 1,3-diketones to tetra-substituted furan skeleton compounds in carbon dioxide (CO2) atmosphere under mild conditions. It was found that...