Synthesis of 4,5-diaryl-1,2,3-benzenetricarboxylates by reaction of 4-hydroxycyclopent-2-en-1-one-2-carboxylates with dimethyl acetylenedicarboxylate

On the absolute photoionization cross section and threshold photoelectron spectrum of two reactive ketenes in lignin valorization: fulvenone and 2-carbonyl cyclohexadienone

We report the absolute photoionization cross section (PICS) of fulvenone and 2-carbonyl cyclohexadienone, two crucial ketene intermediates in lignin pyrolysis, combustion and organic synthesis. Both species were generated in situ by pyrolyzing salicylamide and dectected via imaging photoelectron photoion coincidence spectroscopy. In a deamination reaction, salicylamide loses ammonia yielding 2-carbonyl cyclohexadienone, a ketoketene, which further decarbonylates at higher pyrolysis temperatures to form fulvenone. We recorded the threshold photoelectron spectrum of the ketoketene and assigned the ground state (X̃⁺²A′′ ← X̃¹A′) and excited state (Ã⁺²A′ ← X̃¹A′) bands with the help of Franck–Condon simulations. Adiabatic ionization energies are 8.35 ± 0.01 and 9.19 ± 0.01 eV. In a minor reaction channel, the ketoketene isomerizes to benzpropiolactone, which decomposes subsequently to benzyne by CO₂ loss. Potential energy surface and RRKM rate constant calculations agree with our experimental observations that the decarbonylation to fulvenone outcompetes the decarboxylation to benzyne by almost two orders of magnitude. The absolute PICS of fulvenone at 10.48 eV was determined to be 18.8 ± 3.8 Mb using NH₃ as a calibrant. The PICS of 2-carbonyl cyclohexadienone was found to be 21.5 ± 8.6 Mb at 9 eV. Our PICS measument will enable the quantification of reactive ketenes in lignin valorization and combustion processes using photoionization techniques and provide advanced mechanistic and kinetics insights to aid the bottom-up optimization of such processes.

The absolute photoionization cross section (PICS) of these crucial ketene intermediates supports their quantification in lignin pyrolysis, combustion and organic synthesis.

Diastereoselective construction of cyclopent-2-enone-4-ols from aldehydes and 1,2-allenones catalyzed by N-heterocyclic carbene

Cyclopent-2-enone-4-ols have been prepared highly diastereoselectively from readily available aromatic aldehydes and 1,2-allenones catalyzed by N-heterocyclic carbene. Mechanistic studies showed that there are four possible pathways.

4-Hy-droxy-2-methyl-3,4-diphenyl-cyclo-pent-2-en-1-one

The asymmetric unit of title compound, C₁₈H₁₆O₂, contains two mol­ecules with slightly different conformations. In the first mol­ecule, the two phenyl rings make dihedral angles of 84.98 (11)° and the five-membered ring makes dihedral angles of 84.80 (12) and 73.00 (12)° with the phenyl rings; the corresponding angles for the second mol­ecule are 86.74 (11), 81.20 (13) and 71.36 (12)°. O—H⋯O hydrogen bonds between the hy­droxy and carbonyl groups are a feature of the crystal packing, which results in chains extending parallel to [100]. Weak C—H⋯O and C—H⋯π inter­actions are also observed.

Diversity-oriented synthesis of 1-hydroxy-2,4-benzodioates by regioselective [3+3] cyclocondensations of 1,3-bis(silyloxy)-1,3-butadienes with 3-alkoxy- and 3-silyloxy-2-alkoxycarbonyl-2-en-1-ones

1-Hydroxy-3,5-dimethyl-2,4-benzodioates (4-hydroxyisophthalates) were prepared by [3+3] cyclocondensation of 1,3-bis(silyloxy)-1,3-butadienes with 3-ethoxycarbonyl-4-trimethylsilyloxy-3-penten-2-one which is synthesized from (symmetrical) ethyl 2-acetylacetoacetate. The [3+3] cyclization of 1,3-bis(silyloxy)-1,3-butadienes with 3-alkoxy-2-alkoxycarbonyl-2-en-1-ones, readily available by reaction of beta-ketoesters with trialkyl orthoformiates, provide a convenient and regioselective approach to a great variety of 3-substituted 1-hydroxy-2,4-benzodioates that are not readily available by other methods.