Atmospheric Chemistry of CH3CH2OCH3: Kinetics and Mechanism of Reactions with Cl Atoms and OH Radicals

The atmospheric chemistry of methyl ethyl ether, CH₃CH₂OCH₃, was examined using FT‐IR/relative‐rate methods. Hydroxyl radical and chlorine atom rate coefficients of k (CH₃CH₂OCH₃+OH) = (7.53 ± 2.86) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and k (CH₃CH₂OCH₃+Cl) = (2.35 ± 0.43) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ were determined (297 ± 2 K). The Cl rate coefficient determined here is 30% lower than the previous literature value. The atmospheric lifetime for CH₃CH₂OCH₃ is approximately 2 days. The chlorine atom–initiated oxidation of CH₃CH₂OCH₃ gives CH₃C(O)H (9 ± 2%), CH₃CH₂OC(O)H (29 ± 7%), CH₃OC(O)H (19 ± 7%), and CH₃C(O)OCH₃ (17 ± 7%). The IR absorption cross section for CH₃CH₂OCH₃ is (7.97 ± 0.40) × 10⁻¹⁷ cm molecule⁻¹ (1000–3100 cm⁻¹). CH₃CH₂OCH₃ has a negligible impact on the radiative forcing of climate.     

(C6F5)3B Catalyzed Chemoselective and ortho‐Selective Substitution of Phenols with α‐Aryl α‐Diazoesters

The development of an efficient method for the site‐selective substitution of unprotected phenols has long been considered as an attractive but challenging task. Herein, we describe a highly chemo‐ and ortho‐selective substitution reaction of phenols with α‐aryl α‐diazoacetates with commercially available (C₆F₅)₃B as the catalyst. This reaction proceeds under simple and mild conditions with high efficiency, it features a wide substrate scope and can be easily scaled up.     

Interception of Cobalt‐Based Carbene Radicals with α‐Aminoalkyl Radicals: A Tandem Reaction for the Construction of β‐Ester‐γ‐amino Ketones

The interception of cobalt‐based carbene radicals with α‐aminoalkyl radicals was combined with the Kornblum–DeLaMare reaction and provides β‐ester‐γ‐amino ketones, which are otherwise difficult to obtain in high chemoselectivity. Mechanistically, this transformation is an interplay of cobalt‐based carbene radicals, organoradicals, and ionic intermediates and involves the construction of two C? C bonds and one C?O bond in a one‐pot process. The reaction also features a wide substrate scope and is highly efficient and insensitive to moisture and air.     

The Stability of α‐Hydroperoxyalkyl Radicals

High‐level ab initio and Born–Oppenheimer molecular dynamic calculations have been carried out on a series of hydroperoxyalkyl (α‐QOOH) radicals with the aim of investigating the stability and unimolecular decomposition mechanism into QO+OH of these species. Dissociation was shown to take place through rotation of the C?O(OH) bond rather than through elongation of the CO?OH bond. Through the C?O(OH) rotation, the unpaired electron of the radical overlaps with the electron density on the O?OH bond, and from this overlap the C=O π bond forms and the O?OH bond breaks spontaneously. The CH₂OOH, CH(CH₃)OOH, CH(OH)OOH, and α‐hydroperoxycycloheptadienyl radical were found to decompose spontaneously, but the CH(CHO)OOH has a decomposition energy barrier of 5.95 kcal mol^?1 owing to its steric and electronic features. The systems studied in this work provide the first insights into how structural and electronic effects govern the stabilizing influence on elusive α‐QOOH radicals.     

The Chemistry of α-Carbonyl Azo Compounds

α-Carbonyl azo compounds such as diesters of azodicarboxylic acids, diacylazo compounds, and esters of arylazocarboxylic acids are highly reactive. They add e.g. to amines, aromatic compounds, olefins, CH acids, Grignard and diazo compounds, aldehydes, ketones, and ketenes. These reactions can be used for the preparation of triazanes, hydrazones, oxa-diazoline, azomethinimine, and diazetidine derivatives, etc. α,α′-Dicarbonyl azo compounds are among the strongest dienophiles known.     

Heteroleptic [n]Chromoarenophanes: ansa Complexes Derived from [Cr(η5‐C5H5)(η6‐C6H6)]

The synthesis of ansa complexes has been studied intensively owing to their importance as homogeneous catalysts and as precursors of metal‐containing polymers. However, paramagnetic non‐metallocene derivatives are rare and have been limited to examples with vanadium and titanium. Herein, we report an efficient procedure for the selective dilithiation of paramagnetic sandwich complex [Cr(η⁵‐C₅H₅)(η⁶‐C₆H₆)], which allows the preparation of a series of [n]chromoarenophanes (n=1, 2, 3) that feature silicon, germanium, and tin atoms at the bridging positions. The electronic and structural properties of these complexes were probed by X‐ray diffraction analysis, cyclic voltammetry, and by UV/Vis and EPR spectroscopy. The spectroscopic parameters for the strained and less strained complexes (i.e., with multiple‐atom linkers) indicate that the unpaired electron resides primarily in a d orbital on chromium(I); this result was also supported by density functional theory (DFT) calculations. We did not observe a correlation between the experimental UV/Vis and EPR data and the degree of molecular distortion in these ansa complexes. The treatment of tin‐bridged complex [Cr(η⁵‐C₅H₄)(η⁶‐C₆H₅)SntBu₂] with [Pt(PEt₃)₃] results in the non‐regioselective insertion of the low‐valent Pt⁰ fragment into the C_ipso? Sn bonds in both the five‐ and six‐membered rings, thereby furnishing a bimetallic complex. This observed reactivity suggests that ansa complexes of this type are promising starting materials for the synthesis of bimetallic complexes in general and also underline their potential to undergo ring‐opening processes to yield new metal‐containing polymers.     

Titanyl Acetylacetonate as an Efficient Catalyst for Regioselective 1,2‐Reduction of α,β‐Unsaturated Carbonyl Compounds and Conversion of α‐Diketones & Acyloins to Vicinal Diols with Sodium Borohydride

α,β‐Unsaturated aldehydes and ketones were reduced readily and exclusively to their corresponding allylic alcohols with NaBH₄ and catalytic amounts of titanyl acetylacetonate at room temperature. Reduction reactions were carried out in CH₃CN or THF. This reducing system was also efficient for the reduction of α‐diketones and acyloins to their corresponding vicinal diols in CH₃CN.     

Novel Synthesis of α‐Diketones from Bisbenzimidazolium Salt and Grignard Reagents

The reaction of bisbenzimidazolium salt with Grignard reagents and a new synthetic method of a‐diketones from bis‐benzimidazolium salt and Grignard reagents are reported. The structures of all a‐diketones are characterized by elemental analyses, infrared spectroscopy and ¹H NMR spectroscopy. The influences of the various Grignard reagents on the yield of a‐diketones and the mechanism are discussed, and a new convenient synthetic method for a‐diketones is provided.     

3β‐Acetoxy‐5α,6β‐di­hydroxybisnorcholanic acid 2216 lactone

In the title compound, C₂₄H₃₆O₆, the ester linkage in ring A is equatorial. The six‐membered rings A, B and C have chair conformations. The five‐membered ring D adopts a 13β,14α‐half‐chair conformation and the E ring adopts an envelope conformation. The A/B, B/C and C/D ring junctions are trans, whereas the D/E junction is cis.     

6β‐Azido‐7α‐hydroxy‐17‐oxo‐5α‐androstan‐3β‐yl acetate

In the title compound, C₂₁H₃₁N₃O₄, a potential inhibitor of aromatase, all rings are fused trans. Rings A, B and C have chair conformations which are slightly flattened. Ring D has a 14α‐envelope conformation. The steroid nucleus has a small twist, as shown by the C19—C10⋯C13—C18 torsion angle of 6.6 (2)°. Ab initio calculations of the equilibrium geometry of the mol­ecule reproduce this small twist, which appears to be due to the steric effect of the 6β‐azide substituent rather than to packing effects.     

Transition‐Metal‐Free Formal Decarboxylative Coupling of α‐Oxocarboxylates with α‐Bromoketones under Neutral Conditions: A Simple Access to 1,3‐Diketones

A transition‐metal‐free formal decarboxylative coupling reaction between α‐oxocarboxylates and α‐bromoketones to synthesize 1,3‐diketone derivatives is presented. In this reaction, a broad scope of substrates can be employed, and neither a metal‐based reagent nor an additional base is required. DFT calculations reveal that this reaction proceeds through a coupling followed by decarboxylation mechanism and the α‐bromoketone unprecedentedly serves as a nucleophile under neutral conditions. The rate‐determining step is an unusual hydrogen‐bond‐assisted enolate formation by thermolysis.     

Synthesis of Conjugated Polyphenylene Dendritic β-Diketones

An efficient synthesis of high generation conjugated polyphenylene dendrimer-based β-diketones was investi- gated using simple synthetic methods. The new dendrimer-based β-diketones were characterized by NMR, MS and elemental analysis. The UV-Vis and fluorescence spectra of these β-diketones in different solvents were investigated The photoluminescent （PL） quantum yield and TG and DSC curves were also investigated. A new intermediate, 1-bromo-3,5-diiodobenzene, was developed to synthesize high generation dendrimers with good yields.     

Molecular Diversity of Three‐Component Reaction of β‐Enamino Imide,Malononitrile and Cyclic α‐Diketones

The base promoted three‐component reaction of β‐ enamino imide, malononitrile and various cyclic α‐ diketones in acetonitrile showed interesting molecular diversity. The reactions with acenaphthylene‐1,2‐dione and ninhydrin afforded functionalized spiro[indene‐2,4'‐pyrrolo[3,4‐b ]pyridines] and spiro[acenaphthylene‐1,4'‐pyrrolo[3,4‐b ]pyridines] in good yields. The similar reaction of phenanthrene‐9,10‐dione resulted in the formation of the unexpected complex phenanthro[9',10':4,5]furo[2,3‐c ]pyrrolo[3,4‐b ]pyrroles in satisfactory yields.     

5β,6β‐Epoxy‐17‐oxoandrostan‐3β‐yl acetate and 5β,6β‐epoxy‐20‐oxopregnan‐3β‐yl acetate

In the title compounds, C₂₁H₃₀O₄, (I), and C₂₃H₃₄O₄, (II), respectively, which are valuable intermediates in the synthesis of important steroid derivatives, rings A and B are cis‐(5β,10β)‐fused. The two molecules have similar conformations of rings A, B and C. The presence of the 5β,6β‐epoxide group induces a significant twist of the steroid nucleus and a strong flattening of the B ring. The different C17 substituents result in different conformations for ring D. Cohesion of the molecular packing is achieved in both compounds only by weak intermolecular interactions. The geometries of the molecules in the crystalline environment are compared with those of the free molecules as given by ab initio Roothan Hartree–Fock calculations. We show in this work that quantum mechanical ab initio methods reproduce well the details of the conformation of these molecules, including a large twist of the steroid nucleus. The calculated twist values are comparable, but are larger than the observed values, indicating a possible small effect of the crystal packing on the twist angles.     

Reactions of α,β‐Unsaturated Thioamides with Diazo Compounds

Several reactions of the α,β‐unsaturated thioamide 8 with diazo compounds 1a – 1d were investigated. The reactions with CH₂N₂ ( 1a ), diazocyclohexane ( 1b ), and phenyldiazomethane ( 1c ) proceeded via a 1,3‐dipolar cycloaddition of the diazo dipole at the C?C bond to give the corresponding 4,5‐dihydro‐1H‐pyrazole‐3‐carbothioamides 12a – 12c , i.e., the regioisomer which arose from the bond formation between the N‐terminus of the diazo compound and the C(α)‐atom of 8 . In the reaction of 1a with 8 , the initially formed cycloadduct, the 4,5‐dihydro‐3H‐pyrazole‐3‐carbothioamide 11a , was obtained after a short reaction time. In the case of 1c , two tautomers 12c and 12c ′ were formed, which, by derivatization with 2‐chlorobenzoyl chloride 14 , led to the crystalline products 15 and 15 ′. Their structures were established by X‐ray crystallography. From the reaction of 8 and ethyl diazoacetate ( 1d ), the opposite regioisomer 13 was formed. The monosubstituted thioamide 16 reacted with 1a to give the unstable 4,5‐dihydro‐1H‐pyrazole‐3‐carbothioamide 17 .