Harnessing [1,4], [1,5], and [1,6] Anionic Fries‐type Rearrangements by Reaction‐Time Control in Flow

A series of anionic Fries‐type rearrangements of carbamoyl‐substituted aryllithium intermediates were controlled by using flow microreactor systems. For the [1,4] and [1,5] rearrangements, the aryllithium intermediate formed before carbamoyl migration and the lithium alkoxide formed after carbamoyl migration can be selectively subjected to subsequent reactions with electrophiles by precisely controlling the residence time and temperature (−25 to −50 °C). In contrast, the [1,6] rearrangement is rather slow even at −25 °C. The absence of crossover products indicates the intramolecular nature of the carbamoyl group migration.     

Control of Axial Chirality by Planar Chirality Based on Optically Active [2.2]Paracyclophane

Optically active X-shaped molecules based on the planar chiral [2.2]paracyclophane building block were prepared, in which di(methoxy)terphenyl units were stacked on the central benzene rings. At 25 °C, anisolyl rings freely rotate in solution, while in the crystal form, they are fixed by intramolecular CH–π interactions, thereby leading to the expression of the axial chirality, i.e., propeller chirality was exhibited by the planar chiral [2.2]paracyclophane moiety. The X-shaped molecule exhibited good circularly polarized luminescence (CPL) profiles with moderate Φ_PL and a large g_lum value in the order of 10⁻³ at 25 °C, in solution. In contrast, at −120 °C, dual CPL emission with opposite signs was observed. According to the theoretical studies, the rotary motion of the anisolyl units is suppressed in the excited states, and so emission from two isomers could be observed. These results demonstrate that the axial chirality was controlled by the planar chirality, leading ultimately to propeller chirality.     

Enantioselective 1,4-addition of aryllithium reagents to α,β-unsaturated tert-butyl esters in the presence of chiral additives

Reaction of t-BuLi with a mixture of aryl bromide and chiral diamine, amino ether or diether, in toluene at −78°C provided chiral aryllithium complexes efficiently. Reaction of these aryllithium complexes with α,β-unsaturated tert-butyl esters afforded the 1,4-addition products in up to 88% ee.     

[η3-methallyl-nickel-dad]PF6 complex: new catalyst precursor for ethylene polymerization

The complex [η³-methallyl-nickel-dad]PF₆ is a new catalyst precursor for ethylene polymerization. The system is active in the presence of usual organoaluminium compounds like diethylaluminium chloride, at low Al/Ni ratios and under mild reaction conditions (temperatures between −10°C and 25°C, ethylene partial pressure from 1 to 15 atm). The polymers show extensive methyl branching, whose content is controlled by reaction parameters like temperature and ethylene pressure.     

Studies on organolanthanide complexes: VIII. Synthesis and thermal decomposition of new σ-bonded 1,1′-trimethylenedicyclopentadienyl-early lanthanide complexes

1,1′-Trimethylenedicyclopentadienyl-early lanthanide chlorides, [C₅H₄CH₂)₃-C₅H₄]LnCl · THF, in THF at −70°C reacted with aryllithium or alkyllithium, producing seven new THF solvated LnC σ-bonded 1,1′-trimethylenedicyclopentadienyl-early lanthanide complexes. The yttrium analogue was also synthesized. Their structures were determined by elemental analysis, infrared spectra, mass spectra, ¹H NMR and thermoanalyses. The thermal decomposition of the complexes obtained was studied at ambient temperature or 100°C.     

The thermal rearrangement of endo-7-methyl-exo-7-vinylbicyclo[3.2.0]Hept-2-ene

Gas-phase thermolysis of the title compound in the temperature range of 150°–166°C yields predominantly cis-6-methyl-4,7,8,9-tetrahydroindene by tandem [1,3]–[3,3) sigmatropic shifts: however, we cannot exclude some direct conversion by an alternative [1,3] sigmatropic migration.     

Dimethylenebicyclo[1.1.1]pentanone

The highly strained and reactive dimethylenebicyclo[1.1.1]pentanone (I), was prepared as follows. Treatment of 1,5-bis(chloromethyl)tricyclo[2.1.0.0^{2, 5}]pentan-3-one diethyl ketal (III) with di-t-butyl hydrazodicarboxylate (VII), followed by pyridinium p-toluenesulfonate and trifluoroacetic acid, yielded the keto hydrazine X which was oxidized to the desired ketone I. The ketone I decomposes very rapidly above −30°C.     

Degenerate and nondegenerate rearrangements of the 7-borabicyclo[..1]heptadiene system: Twofold [1,3] supra-facial sigmatropic migrations and anionic [1,] carbon-boron shifts

Two notable skeletal rearrangements of the 7-borabicyclo[..1]heptadiene system (III) have been uncovered: (1) a facile, degenerate, net twofold [1,] suprafacial sigmatropic migration of the 7-substituted boro group, observable by NMR spectroscopy when the carbon centers of the borole (I) and alkyne (II) bear suitable groups; and () a nondegenerate, anionic [1,] aryl shift from carbon to boron, converting the 7,7-dimethylborate salt of III into an aryl(dimethyl)pentaarylborate salt. Thus, the degenerate rearrangement was revealed when pentaphenylborole (Ia) was allowed to react with di-p-tolylacetylene (IIb) at 5°C; the resulting 7-borabicyclo[..1] heptadiene (III) formed displayed NMR methyl signals characteristic of p-tolyl groups located at both C⁵ and C⁶, as well as C⁴ and C⁵. Similarly, the nondegenerate, disruptive anionic isomerization of the 7,7-dimethylborate salt of IIIe or IVe was found to involve migration of either phenyl or p-tolyl groups from carbon to boron, showing that both phenyl (IIIe) and p-tolyl groups (IVe) were located at the bridgeheads in the precursors to VI.     

Equilibria in aqueous solution between Be(II) and iminodiacetic,N-methyliminodiacetic,N-ethyliminodiacetic and N-propyliminodiacetic acids

The complex species formed in aqueous solution between Be(II) and iminodiacetic, N-methyliminodiacetic, N-ethyliminodiacetic and N -propyliminodiacetic acids were studied at 25°C and ionic strength 0.5 M in Na ClO₄. The application of the least-squares computer program LETAGROP to the experimental potentiometric data, taking into account hydrolysis of the Be(II) ion, indicates that, upon varying the ligand-metal relationship, only the monohydroxide complex [Be(OH)C]⁻ (H₂C ligand) is formed in significant amounts for the four systems studied. The formation constants β_pr (11, − 11 and −21) of the protonated species of the ligands, β_pq(− 12 and − 33) of the hydrolytic species of Be(II), and β_pqr(− 311) of the complex [Be(OH)C]⁻ were determined.     

Kinetics of the thermal decomposition of 1,2-dioxaspiro[2,5]octane

The products and kinetics of the thermolysis of 1,2-dioxaspiro[2,5]octane in cyclohexanone and cyclohexanone-CCl₄ mixtures are studied. 1,2-Dioxaspiro[2,5]octane is consumed via two parallel routes: isomerization to oxepan-2-one and solvent (cyclohexanone) oxidation with the partial escape of radicals from the cage (17% at 25 °C). Under an inert atmosphere, the alkyl radicals formed by solvent oxidation initiate the chain radical decomposition of 1,2-dioxaspiro[2,5]octane. The mechanism of 1,2-dioxaspiro[2,5]octane thermolysis is discussed on the basis of the results obtained. The activation parameters of 1,2-dioxaspiro[2,5]octane isomerization to oxepan-2-one and reactions of dioxaspiro[2,5]octane with cyclohexanone are discussed.     

Dense compounds of C,H, N,and O atoms: Nitramine derivatives of diimino- and dioxodecahydro-1 h,5h-diimidazo-[4,5-b:4′,5′-e]pyrazine

Guanidine condensed with 1,4-diformyl-2,3,5,6-tetrahydroxypiperazine 1 to give 2,6-diiminodecahydro-1H,5H-diimidazo[4,5-b:4′,5′-e]pyrazine 3 isolated as the tetrahydrochloride salt. nitric acid (100%) at −40°C converted the bisguanidine 3 to 2,6-dinitrimino-4,8-dinitrodecahydro-1H,5H-diimidazo[4,5-b:4′,5′-e]- pyrazine 8 isolated as a dihydrate, whereas nitration by nitronium tetrafluoroborate at 0° to 25°C afforded 2,6-diimino-4,8-dinitrodecahydro-1H,5H-diimidazo[4,5-b:4′,5′-e]pyrazine 9 isolate as the monohydrated bistetrafluoroborate salt, and treatmetn with nitric acid (100%) and acetic anhydride or phosphorus pentoxide converted the bisguanidine 3 to 2,6-dioxo-1,3,4,5,7,8-hexanitrodecahydro-1H,5H-diimidazo[4,5-b:4′,5′-e]pyrazine 4 , also obtained from the tetra N-nitro compound 8 · 2 H₂O and from the dinitramine 9 · 2 BHF₄ · H₂O after similar treatment. The cis-syn-cis- configuration of the tricyclic bisurea 4 and bisguanidine 9 was confirmed by X-ray crys-tallographic analysis. Nitrosation by nitrous acid or by dinitrogen tetroxide converted the bisguanidine 3 to a hydrated 2,6-dinitrosimino-4,8-dinitrosodecahydro-1H,5H-diimidazo[4,5-b:4′,5′-]pyrazine 10 · 2.5 H₂O, whereas treatment with nitrosonium tetrafluo-roborate afforded the bistetrafluoroborate salt of 4,8-dinitroso derivative 11 · 2 BHF 4 . The nitrosamines 10 and 11 were converted to the tetranitro compound 8 · 2 H₂O on treatment with nitric acid (100%) at −40°C. Treatmnt with fluoroboric acid etherate in acetonitrile converted nitroimino groups in compound 8 · 2 H₂O and nitrosimino groups in compound 10 · 2.5 H₂O to imino groups in compounds 9 · 2 BHF₂ · H₂O and 11 · 2 HBF₄ respectively.     

Umsetzung von C(NMe2)4 mit Ni(CO)4 – Synthesen und Strukturen von [C(NMe2)3][(CO)3NiC(O)NMe2], [C(NMe2)3]2[Ni5(CO)12] und [C(NMe2)3]3[Ni6(CO)12][O2CNMe2]

Reaction of C(NMe₂)₄ with Ni(CO)₄ – Syntheses and Structures of [C(NMe₂)₃][(CO)₃NiC(O)NMe₂], [C(NMe₂)₃]₂[Ni₅(CO)₁₂], and [C(NMe₂)₃]₃[Ni₆(CO)₁₂][O₂CNMe₂] The reaction of C(NMe₂)₄ with Ni(CO)₄ in THF produces the carbamoyl complex [C(NMe₂)₃][(CO)₃NiC(O)NMe₂] ( 1 ); side products are the purple cluster compound [C(NMe₂)₃]₂[Ni₅(CO)₁₂] · THF ( 2 · THF) and the red cocristallization product [C(NMe₂)₃]₃[Ni₆(CO)₁₂][O₂CNMe₂] ( 3 ). All compounds were studied by X‐ray diffraction analyses. The cations of 3 are all disordered but not those of 1 and 2 . The unit cell of 1 contains two crystallographically independent anions (I and II) which differ in the dihedral angle between the plane of the carbamoyl ligand and the plane defined by the atoms C_Carbamoyl–Ni–CO amounting 0° in the anion I and 18° in the anion II.     

K2[O(HgSO3)3], a new sulfitomercurate with an [OHg3] core

The structure of dipotassium μ₃‐oxido‐tris[sulfitomercurate(II)], K₂[O(HgSO₃)₃], is characterized by segregation of the K⁺ cations and complex [O(HgSO₃)₃]²⁻ anions into layers parallel to (010). The anion has m symmetry and is a new example of a μ₃‐oxido‐trimercurate complex with a central [OHg₃] core. This unit adopts the shape of a flat, almost trigonal, pyramid (mean O—Hg = 2.072 Å and mean Hg—O—Hg = 110.8°). The two independent Hg—S bonds have nearly the same length (mean Hg—S = 2.335 Å). Due to intermolecular O...Hg donor–acceptor interactions greater than 2.65 Å, the O—Hg—S fragments are slightly bent. The [KO₉] coordination polyhedron of the K⁺ cation approaches a distorted tricapped trigonal prism with a [6+1+2] coordination.     

The bromination of 3-bromo-6,7-benzobicyclo[3.2.1]octa-2,6-diene

The bromination of 3-bromo-6, 7-benzobicyclo [3.2.1] octa-2, 6-diene at ?50°C has been found to give only one product, the tribromide(7) produced via Wagner-Meerwein rearrangement with accompanying aryl migration. The bromination at 0°C produced nonrearranged tribromides beside the rearranged product. The structures of the products were determined by means of spectral data. The addition mechanism is discussed in terms of exo- and endo-attack.     

Acyl- und Alkylidenphosphane. XII [1]. Synthese und Eigenschaften des 2,2-Dimethylpropionylphosphans und einiger Derivate

Acyl and alkylidene phosphines. XII. Syntheses and properties of 2,2-dimethylpropionylphosphine and of some derivatives At ?25°C bis(trimethylsilyl)phosphine 1b and 2,2-dimethylpropionyl chloride form (2,2-dimethylpropionyl)trimethylsilylphosphine 2b . As this compound is thermally more stable than similar acyltrimethylsilylphosphines, it might be treated at ?55°C with methyllithium to form the correspondig lithium phosphide 2d ; after the addition of chlorotrimethylsilane [2,2-dimethyl-1-(trimethylsiloxy)propylidene]-trimethylsilylphosphine 3c is obtained. At +20°C 2b rearranges to the E and Z isomer of [2,2-dimethyl-1-(trimethylsiloxy)propylidene]phosphine 3b . The NMR data of E- 3b and Z- 3b differ mostly in the coupling constants. Kept in the diffuse daylight for several days 3b dimerizes to form 2,4-di(tert.butyl)-2,4-bis(trimethylsiloxy)-1,3-diphosphetane 10 . In solution 10 is unstable and decomposes again to a mixture of the E und Z isomer of 3b . Reacting 3b or 3c with alcoholes all trimethylsilyl groups are replaced by hydrogen atoms and unstable 2,2-dimethylpropionylphosphane 4b is formed. Lithium(2,2-dimethylpropionyl)phosphide 4d , synthesized at ?60°C from 4b and methyllithium, crystallizes with one molecule 1,2-dimethoxyethane per formula unit and is dimeric in benzene. As shown by the NMR data 4d has the structure of an alkylidene-phosphine with the lithium atom bound to oxygen. At ?50°C 4d and chlorotrimethylsilane react to form 3b .     

Alternating copolymerization of ethylene and propene with the [ethylene(1-indenyl)(9-fluorenyl)]zirconium dichloridemethylaluminoxane catalyst system

The copolymerization of ethylene and propene was conducted at −40°C with the [ethylene(1-indenyl)(9-fluorenyl)]zirconium dichloride-methylaluminoxane catalyst system, and the microstructure of the resulting copolymers was analyzed in detail by ¹³C NMR. The content of alternating [EP] sequences increased markedly with an increase in the feed ratio of propene to ethylene. A poly(ethylene-co-propene) with a proportion of [EP] sequences over 95% was thus obtained under appropriate copolymerization conditions. It was also demonstrated that the alternating ethylene-propene copolymer is stereoregular and isotactic.     

Bis‐Lactam Peptide [i,i + 4]‐Stapling

Even though the bis‐lactam peptide stapling with the [i, i + 7] and the [i, i + 11] systems has been known to be able to afford % α‐helicity values up to 100% (25°C), the performance of the bis‐lactam peptide stapling with the [i, i + 4] system in current literature has been mediocre (% α‐helicity ≦40%, 25°C). In the current study, we found that high % α‐helicity is also obtainable with the bis‐lactam [i, i + 4]‐stapling by demonstrating with our model peptide sequence that the bis‐lactam [i, i + 4]‐stapling with N^ε‐para‐phenylenediacetyl‐lysine was able to afford a % α‐helicity value of ~64.1% (25°C). Therefore, the bis‐lactam [i, i + 4]‐stapling could also be an efficacious peptide stapling mode that can be employed for biomedical applications.     

CH3--MoF], [CH2=MoHF], and [CH[triple bond]MoH2F] formed by reaction of laser-ablated molybdenum atoms with methyl fluoride: persistent photoreversible interconversion through alpha-hydrogen migration and agostic interaction

Simple molybdenum methyl, carbene, and carbyne complexes, [CH3--MoF], [CH2=MoHF], and [CH[triple chemical bond]MoH(2)F], were formed by the reaction of laser-ablated molybdenum atoms with methyl fluoride and isolated in an argon matrix. These molecules provide a persistent photoreversible system through alpha-hydrogen migration between the carbon and metal atoms: The methyl and carbene complexes are produced by applying UV irradiation (240-380 nm) while the carbyne complex is depleted, and the process reverses on irradiation with visible light (lambda>420 nm). An absorption at 589.3 cm(-1) is attributed to the Mo--F stretching mode of [CH3--MoF], which is in fact the most stable of the plausible products. Density functional theory calculations show that one of the alpha-hydrogen atoms of the carbene complex is considerably bent toward the metal atom (angle-spherical HCMo=84.5 degrees ), which provides evidence of a strong agostic interaction in the triplet ground state. The calculated C[triple chemical bond]Mo bond length in the carbyne is in the range of triple-bond values in methylidyne complexes.     

Formation of 3-Sulfonyl-Substituted Benzo[a]heptalene-2,4-diols from Heptalene-1,2-dicarboxylates and Lithiomethyl Phenyl Sulfones

On treatment with 6 mol-equiv. of lithiomethyl phenyl sulfone at −78° in THF, dimethyl 5,6,8,10-tetramethylheptalene-1,2-dicarboxylate ( 1′b ) gives, after raising the temperature to −10° and addition of 6 mol-equiv. of BuLi, followed by further warming to ambient temperature, the corresponding 3-(phenylsulfonyl)benzo[a]heptalene-2,4-diol 2b in yields up to 65% (cf. Scheme 6 and Table 2), in contrast to its double-bond-shifted (DBS) isomer 1b which gave 2b in a yield of only 6% [1]. The bisanion [ 9 ]²⁻ of the cyclopenta[a]heptalen-1(1H)-one 9 (cf. Fig. 1), carrying a (phenylsulfonyl)methyl substituent at C(11b), seems to be a key intermediate on the reaction path to 2b , because 9 is transformed in high yield into 2b in the presence of 6 mol-equiv. of BuLi in the temperature range of −10° to room temperature (cf. Scheme 7). Heptalene-dicarboxylate 1′b was also transformed into benzo[a]heptalene-2,4-diols 2c – g by a number of lithiated methyl X-phenyl sulfones and BuLi (cf. Scheme 9 and Table 3).     

Sequential thermal rearrangements of syn-9-vinyl-bicyclo[6.1.0]-nona-2,4,6-triene

The title compound 1-syn at 65°C undergoes a cascade of thermal rearrangements to yield tetracyclo[5.4.0.0.^2,11O^4,10]undeca-5, 8-diene (5). The kinetics for the isomerization of the intermediate bicyclo(4.3.2]-undeca-2,4,7,10-tetraene (3) have been measured.