Photolytic decarbonylation of o-benzoquinones

It was established that photodecarbonylation of o-benzoquinones occurs by irradiation not only by UV-light, but visible light (λ>520 nm) too. Study of the series of 4,5-di-substituted 3,6-di-tert-butyl-o-benzoquinones detected that the only product of photoreaction is the corresponding 3,4-di-substituted 2,5-di-tert-butyl-cyclopentadienone, which is formed in a yield close to quantitative. NMR monitoring of reaction of photodecarbonylation of o-benzoquinones detected that this is a two-stage process. In the first stage the photoexcited molecule of quinone rearranges into bicyclo compound (bicyclo[1.3.0]hexa-3-en-2,6-dione) containing five- and three- membered cycles, which spontaneously decomposes during the following dark stage into cyclopentadienone and a molecule of CO.     

One-pot synthesis of cyclopentadienones through ring contraction of 2H-pyran-2-ones

A one-pot synthesis of 2,3,5-trisubstituted cyclopentadienones has been delineated through ring contraction of suitably functionalized 2H-pyran-2-ones using either cyanoacetamide or methyl cyanoacetate.     

DABCO-triggered mild cascade reaction of electron-deficient cyclopentadienone: facile and efficient synthesis of condensed carbocycles

2,5-Bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone (1) reacts with 4-phenylbut-3-yn-2-one (2b) in the presence of DABCO to give the bicyclic carbocycles (6b) and the tetracyclic carbocycle (7b) under extremely mild reaction conditions.     

Cyclopentadiene combustion in a plug flow reactor near 1150 K

Cyclopentadienyl (CPDyl) was generated for study by oxidizing and pyrolizing 1,3-cyclopentadiene (CPD) in Princeton’s adiabatic, atmospheric pressure flow reactor. This study used nitrogen carrier gas, initial CPD concentrations from 1000 to 3000 ppm by volume (ppmv), equivalence ratios from fuel lean (? = 0.6) to pyrolytic conditions (? = 100) and initial temperatures from 1100 to 1200 K. The reaction progress was followed from 5 to 150 ms using a water cooled sample probe and GC-FID analysis of C₁-C₁₄ species. The oxidation results show that CPD and CPDyl react via 19 pathways to yield 22 hydrocarbon intermediates. Analysis of the oxidative CPDyl ring opening pathways reveals the importance of the 2,4-cyclopentadienoxy (c-C₅H₅O) β-scission reaction: c-C₅H₅O ↔ CHCH-CHCH-CHO. The fastest theoretical mechanism has a calculated unimolecular high-pressure rate constant of 2.00 × 10¹³e^−7215/T s⁻¹ which is seven orders of magnitude larger at 1150 K than the previous literature estimate. Cyclopentadienone (CPDone) has been assumed to be an important intermediate in C₅ ring oxidation even though it has not been unambiguously identified in the combustion environment. A detection limit of 20 ppmv for CPDone in the present apparatus failed to note any CPDone. A set of mechanistic pathways for the C₅ ring oxidation includes steps to avoid unrealistic CPDone production is presented. The complex mechanism illustrates the need for detailed models to understand the combustion of aromatics and soot precursors. The article stresses the importance of CPDyl in the formation of aromatic rings during combustion, which subsequently leads to polycyclic aromatic hydrocarbons (PAH) and soot precursors.     

Stereoselective conjugate additions of Grignard reagents to cyclopentadienones

Conjugate addition reactions of Grignard reagents with cyclopentadienones having trimethylsilyl groups at the α and α′ positions, and 1-hydroxyethyl substitutents at the β and β′ positions, are reported; excellent stereoselectivity was observed and the relative stereochemistry of three of the products was determined by X-ray methods.     

Chiral (cyclopentadienone)iron complexes with a stereogenic plane as pre-catalysts for the asymmetric hydrogenation of polar double bonds

In this paper, we describe a small library of easy-to-prepare chiral (cyclopentadienone)iron pre-catalysts for enantioselective CO and CN hydrogenations. Starting from readily accessible achiral materials, six chiral (cyclopentadienone)iron complexes (1a-f) possessing a stereogenic plane were synthesized in racemic form. Based on the screening of pre-catalysts (±)-1a-f in the hydrogenation of ketones and ketimines, we selected two complexes (1a and 1d) for resolution by semipreparative enantioselective HPLC. The absolute configuration of the separated enantiomers of 1a and 1d was assigned by XRD analysis (1a) and by comparison between experimental and DFT-calculated ECD and ORD spectra (1d). The enantiopure pre-catalysts (S)-1a and (R)-1d were tested in the asymmetric hydrogenation of several ketones and ketimines and showed good activity and modest enantioselectivity, the e.e. values ranging from very low to moderate (54%).     

Breaking the symmetry in the molecular motor family: synthesis of a dissymmetrized pentaphenyl cyclopentadienyl ligand and its ruthenium tris(indazolyl)borate complex

In order to demonstrate a movement of rotation in a family of rotary molecular motors, 1-bromo-1-(4-tolyl)-2,3,4,5-tetra(4-bromophenyl) cyclopentadiene has been synthesized. The coordination of this C_2v cyclopentadiene to a ruthenium trisindazolylborate complex and the quadruple coupling reaction with ethynylferrocene led to the dissymmetrized motor (1).     

(Cyclopentadienone)iron Complexes: Synthesis,Mechanism and Applications in Organic Synthesis

(Cyclopentadienone)iron tricarbonyl complexes are catalytically active, inexpensive, easily accessible and air-stable that are extensively studied as an active pre-catalyst in homogeneous catalysis. Its versatile catalytic activity arises exclusively due to the presence of a non-innocent ligand, which can trigger its unique redox properties effectively. These complexes have been employed widely in (transfer)hydrogenation (e. g., reduction of polar multiple bonds, Oppenauer-type oxidation of alcohols), C−C and C−N bond formation (e. g., reductive aminations, α-alkylation of ketones) and other synthetic transformations. In this review, we discuss the remarkable advancement of its various synthetic applications along with synthesis and mechanistic studies, until February 2021.     

Directed synthesis of symmetric and dissymmetric molecular motors built around a ruthenium cyclopentadienyl tris(indazolyl)borate complex

This article focuses on the synthesis of a family of rotary molecular motors based on a penta-substituted cyclopentadienyl tris(indazolyl)borate ruthenium(II) complex. In order to demonstrate a movement of rotation in this family of molecular motors, dissymmetric derivatives with one ferrocene missing have also been synthesized. The molecules have been prepared with ester and thioether-functionalized tris(indazolyl)borate ligands in view of studying them as single molecules on various surfaces by STM or AFM techniques.