Mechanisms of mass spectrometric fragmentations: X–Interaction between remote or-groups in decalin-1,5-diols and their dimethyl ethers

The mass spectra of the five stereoisomers of decalin-1,5-diol and its dimethyl ether have been investigated. The differences in the mass spectra of stereoisomers I to III with a trans- decalin ting system are small. The differences are much larger in the mass spectra of the two isomers IV and V of the cis-decalin series and the elimination of CH₂O, formed by interaction between the two methoxy groups, from the molecular ion is only observed in the mass spectrum of Vb.     

Zum Mechanismus massenspektrometrischer Fragmentierungsreaktionen—IXSterische Effekte in den Massenspekten der Stereoisomeren von Decalin-2,3-diolen,Decalin-2,4-Diolen und Ihen Dimethyläthern

The mass spectra of all stereoisomers of decalin-2,3-diol, the corresponding dimethyl ethers and of some deuterated derivatives are discussed. The mass spectra of isomeric decalin-2,3-diols differ only slightly in ion intensities. The mass spectra of the stereoisomeric 2,3-dimethoxy-decalins are nearly identical within the series of transand cisderivatives. A mass spectrometric identification of the stereoisomers of these compounds is therefore diffucult. Stereoselective eliminations from the molecular ion are not observed. The mass spectra -of stereoisomeric decalin-1,4-diols show characteristic differences in the intensities of the[M ? H₂O]⁺˙-ions, which can be related to the geometry of the molecules in a similiar mode as was the case with cyclohexane-1,4-diols, The sterechemical control of the elimination of H₂O from the molecular ions has been confirmed by deuterium labelling. The mass spectra of stereoismeric 1,4-dimethoxy-decalins also differ characteristically in the intensities of the [M ? CH₃OH]⁺˙ ions. Furthermore peak due to the [M ? CH₂O]⁺˙ ions are only observed in the mass spectra of those stereoisomers, which have at least one conformation with a short distance between the two methoxy. The stereospecifity of the CH₃OH- and CH₂O-eliminationjs has also been determined by deuterium labelling.     

Stereoselective syntheses and transformations of chiral 1,3-aminoalcohols and 1,3-diols derived from nopinone

A library of 1,3-difunctionalized pinane derivatives were synthesized and applied as chiral catalysts in the addition of diethylzinc to benzaldehyde. 1,3-Aminoalcohol 6a was prepared from (−)-nopinone 2 via stereoselective Mannich condensation and reduction of the resulting β-amino ketone 4. The key aminoalcohol 6a was transformed into primary, secondary and tertiary substituted aminoalcohols in order to study the effect of the substituent on catalytic activity. Starting from (−)-nopinone, cis- and trans-β-hydroxy esters 15 and 16 were prepared in a two-step stereoselective synthesis. Reduction of the hydroxy esters resulted in pinane-based 1,3-diols, while hydrolysis of the esters, followed by DCC-mediated amidation and subsequent reduction, led to cis- and trans-N-benzyl-1,3-aminoalcohols 8 and 23. trans-N-Benzyl-1,3-aminoalcohol 8 was also prepared by selective mono-debenzylation of 6a via a continuous-flow process in an H-Cube® system. The resulting aminoalcohols and diols were applied as chiral catalysts in the reaction of diethylzinc and benzaldehyde.     

Acid catalyzed rearrangements in bicyclo[3.3.1]nonanes : 2-Substituted-6-(1,3-dioxolan-2-yl)-cyclooctanones from 1-substituted-2-hydroxy-9,9-(ethylenedioxy)-bicyclo[3.3.1]-nonanes

Treatment of endo-2 or exo-2-hydroxy-1-substituted ketals 1a–d with p-toluensulfonic acid in dry benzene results in a reversible C₉ bridge cleavage and affords equilibrium mixtures where 2-substituted-6-(1,3-dioxolan-2-yl)cyclooctanones 6a–d are present as main products. Yields in 6a–d are present as the steric hindrance of the substituents at C₁ in the substrate increases as well. Deuterium exchange experiments are in favour of an intramolecular 1,3-hydride shift from C₂ to C₉.     

A study of the fragmentation of cyclopentane-1,3-diols and of cyclopentane-1,2,4-triols

The mass spectra of the two cyclopentane-1,3-diol and of the three cyclopentane-1,2,4-triol stereoisomers have been studied. Extensive deuterium labelling allows the detection of complex processes, especially for the elimination of water from the [M – H_2OO]⁺· and [M]⁺· ions.     

Synthesis of 2-phenyl-1,3-di(4-pyridyl)naphthvalene by photoinduced reversible valence isomerization of 2-phenyl-1,3-di(4-pyridyl)naphthalene

2-Phenyl-1,3-di(4-pyridyl)naphthvalene 3a was synthesized by the photoinduced reversible valence isomerization of 2-phenyl-1,3-di(4-pyridyl)naphthalene 2a. Then, 3a was converted into 3-phenyl-1,2-di(4-pyridyl)naphthalene 4a and 2a simultaneously. The t_1/2 of 3a in DMSO-d₆ at 90 °C was 2 h, while that at 110 °C was approximately 10 min.     

Easy and efficient deracemization of all trans-1,3-diphenyl-2,4-bis-[α-hydroxybenzyl]-cyclobutane and its bisphenylsulfanyl derivative and the assignment of the absolute configuration

An effective deracemization of all trans-1,3-diphenyl-2,4-bis-[α-hydroxybenzyl]-cyclobutane 1 was achieved by the application of the (R)-(?)-O-acylmandelic acid as a resolving agent, followed by the crystallization of the diastereomeric esters. The kinetic resolution was also observed in the esterification. Racemic 1 was transformed into bisphenylsulfanyl derivative 3. Enantioselective oxidation of 3 with a VO(acac)₂-chiral Schiff Base catalytic system led to a kinetic resolution, and highly enantiomerically enriched bissulfides/bissulfoxides were isolated. Assignment of the absolute configuration was made by spectroscopic methods and chemical correlation. Due to the rigid C₂-symmetric framework, chiral compounds 1 and 3 have strong steric requirements and may be useful in chiral recognition.     

Lipase mediated enantiomer and diastereomer separation of 2,2′-[1,2- and 1,3-phenylenebis(oxy)]dicyclohexanols

Separation of diastereomeric and enantiomeric mixtures of 2,2′-[1,2- and 1,3-phenylenebis(oxy)]dicyclohexanols rac-3a and meso-3a, and rac-3b and meso-3b—resulting from the reactions of pyrocatechol 1a and resorcinol 1b with cyclohexene oxide 2—were performed using acetylation catalyzed by the highly stereoselective Candida antarctica lipase B (Novozym 435). The absolute configurations of the resulting diols (S,S,S,S)-3a,b, monoacetates (R,R,S,S)-4a,b and diacetates (R,R,R,R)-5a,b were assigned on the basis of the steric analogy to the acetylation of racemic trans-2-phenoxycyclohexanol rac-6 with the same enzyme resulting in the known acetate (−)-(R,R)-7.     

Synthesis and structure of 1,3-bis(hydroxysilyl)-2,4-dimethyl-2,4-diphenylcyclodisilazane

Trans-silylation reactions of (Me₃Si)₂NH with PhRSiCl₂ (R = Me, Ph) gave HN(SiMePhCl)₂ (1) or ClMePhSiNHSiPh₂Cl (2). The treatment of 1,3-dichlorodisilazane (1 or 2) with an equimolar amount of n-BuLi led to the formation of 1,3-bis(chloro-silyl)-2,4-dimethyl-2,4-diphenylcyclodisilazane (ClSiMePh)₂(NSiMePh)₂ (3) or (ClSiPh₂)₂(NSiMePh)₂ (4), which was allowed to hydrolyze to form 1,3-bis(hydroxysilyl)-2,4-dimethyl-2,4-diphenylcyclodisilazane (HOSiMePh)₂(NSiMePh)₂ (5) or (HOSiPh₂)₂(NSiMePh)₂ (6), respectively. The cyclodisilazane monomers were characterized by elemental analysis, NMR and IR spectroscopy. Compound 3 was obtained as a 4:6 cis/trans mixture while 4 adopted trans-structure considering the hindrance of pendent groups. In addition, the molecular structures of trans-5 and trans-6 were determined by X-ray crystallographic analysis and discussed in detail.     

Syntheses and conformational analyses of new naphth[1,2-e][1,3]oxazino[3,2-c]quinazolin-13-ones

The syntheses of naphth[1,2-e][1,3]oxazino[3,2-c]quinazolin-13-one derivatives (3a–f) were achieved by the solvent-free heating of benzyloxycarbonyl-protected intermediates (2a–f) with MeONa. For intermediates 2a–f, prepared by the reactions of substituted aminonaphthols with benzyl N-(2-formylphenyl)carbamate, not only the expected trans ring form B and chain form A¹, but also the rearranged chain form A² as a new tautomer were detected in DMSO at room temperature. The quantity of A² in the tautomeric mixture was changed with time.Conformational analyses of the target heterocycles 3a–f by NMR spectroscopy and accompanying theoretical calculations at the DFT level of theory revealed that the oxazine ring preferred a twisted chair conformation and the quinazolone ring was planar. Besides the conformations, both the configurations at C-7a and C-15 and the preferred rotamers of the 1-naphthyl substituent at C-15 were assigned, which allowed evaluation of the aryl substituent-dependent steric hindrance in this part of the molecules. Configurational assignments were corroborated by quantifying the ring current effect of 15-aryl in terms of spatial NICS.     

Stereochemical studies-XXXIII. Saturated heterocycles-IX: Synthesis and conformations of stereoisomeric cis- and troans-tetramethylene- and pentamethylenedihydro-1,3-oxazines

By the reaction of cis- and trans-2-aminomethylcyclohexanol (1, 2), cis- and trans-2-hydroxymethyl-cyclohexylamine (3,4) and the homologous cycloheptane derivatives (5-8) with ethyl p-chlorobenzimidate (11), cis- and trans-5,6-tetramethylene- and pentamethylene-2,3,5,6-tetrahydro-4H-1,3-oxazines (12,13,16,17) and cis- and trans-4,5-tetramethylene- and pentaimethylene-4,5-dihydro-6H-1,3-oxazines (14, 15, 18, 19) were prepared. The amidine intermediate of the ring-closure reaction was isolated, and the mechanism of the acid-catalysed reaction is discussed. It follows from the ¹H NMR data that in the preferred conformations of the cis-tetramethylene-tetrahydrooxazines the methylene group of the hetero ring is equatorial and the hetero atom (O or N) axial. In contrast, the conformation equilibria of the cis pentamethylene derivatives, in accordance with earlier X-ray analysis, are shifted towards the conformer containing the methylene group in isoclinal and the hetero atom in equatorial position. The preferred conformations 12a and 14a of the tetramethylene derivatives 12 and 14 were also determined by X-ray crystal analysis.     

Polymerization of 1,3-Butadiene Catalyzed by Cobalt(Ⅱ) and Nickel(Ⅱ) Complexes Bearing Pyridine-2-imidate Ligands

Cobalt and nickel complexes (1a-1d and 2a-2d, respectively) supported by 2-imidate-pyridine ligands were synthesized and used for 1,3-butadiene polymerization. The complexes were characterized by IR and element analysis, and complex 1a was further characterized by single-crystal X-ray diffraction. The solid state structure of complex 1a displayed a distorted tetrahedral geometry. Upon activation with ethylaluminum sesquichloride (EASC), all the complexes showed high activities toward 1,3-butadiene polymerization. The cobalt complexes produced polymers with high cis-1,4 contents and high molecular weights, while the nickel complexes displayed low cis-1,4 selectivity and the resulting polymers had low molecular weights. The catalytic activities of the complexes highly depended on the ligand structure. With the increment of polymerization temperature, the cis-1,4 content and the molecular weight of the resulting polymer decreased.     

Synthesis of 1,3-diaryl-1H-benzo[g]indazoles

A facile three-step synthetic route toward 1,3-diaryl-1H-benzo[g]indazoles 1a–1n starting with 3,4-dimethoxy-2-allylbenzaldehyde (6) in modest total yield is described. The facile route was carried by aldol condensation of aldehyde 6 with aryl methyl ketones 5a–5d in alkaline MeOH at reflux, Knorr pyrazole synthesis of the resulting chalcones 4a–4d with aryl hydrazines 3a–3e in EtOH at reflux followed by DDQ-mediated aromatization in toluene at reflux, and oxidative cleavage annulation of olefins 2a–2n with the one-pot combination of OsO₄/NaIO₄/HOAc in the aqueous THF at reflux.     

Syntheses and coordination behaviour of 2-(ortho-phosphinophenyl)-functionalised 1,3-dioxolanes and 1,3-dioxanes towards a [(COD)Rh]-complex fragment - models for immobilised complexes

The syntheses are reported of the ether-phosphine ligands: 2-(ortho-diphenylphosphinophenyl)-1,3-dioxolane (1a), 2-(ortho-diisopropylphosphinophenyl)-1,3-dioxolane (1b), 2-(ortho-diphenylphosphinophenyl)-1,3-dioxane (1c), 2-(ortho-diisopropylphosphinophenyl)-1,3-dioxane (1d). Their reaction with [(COD)RhCl]₂ (COD: 1,5-cyclooctadiene) results in the formation of the mononuclear complexes: {chloro(COD)[2-(ortho-diphenylphosphinophenyl)-1,3-dioxolane]rhodium(I)} (2a), {chloro(COD)[2-(ortho-diisopropylphosphinophenyl)-1,3-dioxolane]rhodium(I)} (2b), {chloro(COD)[2-(ortho-diphenylphosphinophenyl)-1,3-dioxane]rhodium(I)} (2c), and {chloro(COD)[2-(ortho-diisopropylphosphinophenyl)-1,3-dioxane]rhodium(I)} (2d). The chloride ligands of compounds 2a and 2b were abstracted with TlPF₆, with accompanied insertion of an acetal oxygen atom of the ligands 1a and 1b into the coordination sphere of the metal centre, producing {(COD)[η²-P,O-2-(ortho-diphenylphosphinophenyl)-1,3-dioxolane]rhodium(I)}PF₆ (3a∗PF₆) and {(COD)[η²-P,O-2-(ortho-diisopropylphosphinophenyl)-1,3-dioxolane]rhodium(I)}PF₆ (3b∗PF₆). In contrast the dioxane analogues of 3, 3c∗BF₄ and 3d∗BF₄, were formed by reacting the ligands 1c, 1d with [Rh(COD)₂]BF₄. The ligands 1 and the complexes 2 serve as model compounds for their via acetalation to a polyvinylalcohol resin bound analogues. The complexes synthesised were employed as pre-catalysts in the hydroformylation reaction of 1-octene.     

Chemoselective conversion of aromatic epoxide and 1,2-diol to 1,3-dioxane derivatives with phenyltrimethylammonium tribromide in the presence of a catalytic amount of antimony(III) bromide

trans-Stilbene oxide was oxidatively converted to 2-phenyl-1,3-dioxanes with phenyltrimethylammonium tribromide in the presence of various 1,3-diols and a catalytic amount of SbBr₃ in DMSO at room temperature. Aromatic 1,2-diol, such as hydrobenzoin, was similarly converted to 2-aryl-1,3-dioxane derivatives under the same reaction conditions.     

Regioselectivity in the 1,3-dipolar cycloaddition of adamantylidenefulvene and its modification by inclusion in cyclodextrins' solutions

The 1,3-dipolar cycloaddition of adamantylidenefulvene (1) with 2 equiv of nitrile oxides 2a-d gave 1/1 cycloadducts, 3a-d and 4a-d, as the major products, and four other 1/2 minor cycloadducts 5-8a,b. The ratios of 1/1 cycloadducts 3a-d to 4a-d in THF solution were about 1/1 in the four different nitrile oxides 2a-d studied and microwave was found to accelerate the reactions and enhance their yields. It is noteworthy that the regioselectivity of 3a/4a was enhanced to 71/29 in β-cyclodextrin (β-CD) aqueous solution compared to that of 40/60 in the absence of β-CD. The regioselectivity of 3b/4b was further enhanced to 99/1 when 4-tert-butylphenyl hydroximinoyl chloride (9b) was complexed with β-CD and then proceeded to react with 1; this is in sharp contrast with that of 33/67 in the absence of β-CD. The binding constant of 1·β-CD in acetone-d₆/D₂O (1/1) was determined to be 188±9 M⁻¹ by ¹H NMR titration experiments. The binding mode of 1·β-CD was further determined by ROESY experiment. Furthermore, molecular dynamic simulations were carried out to provide information of the complexation modes of 1·β-CD, 3a·β-CD, 4a·β-CD, 9a·β-CD, and 9b·β-CD. It was found that both steric and electrostatic effects play important roles in determining the regio- and stereochemistry of 1,3-dipolar cycloaddition of 1. Finally, β-CD is shown to serve as a chiral shift reagent to differentiate the enantiomers of 4a in ¹H NMR.     

Structure-fluorescence relationship of push-pull 2-phenylbenzothiazole derivatives designed based on the firefly light-emitter

6-Dimethylamino-2-phenylbenzothiazole (1a) mimicking the firefly oxyluciferin structure and the derivatives with an electron-withdrawing substituent on the phenyl group were prepared, and their fluorescence properties were investigated in various solvents. 1a showed solvatochromic fluorescence with good fluorescence quantum yields (Φ_f >0.8). The introduction of an electron-withdrawing group led to a red-shift of the emission maximum. In particular, the derivatives with the 2,2-dicyanoethenyl and (1,3-dihydro-1,3-dioxo-2H-inden-2-ylidene)methyl groups showed near-infrared fluorescence in chloroform. In addition, the derivative with the phenylimine moiety showed efficient solid-state fluorescence, resulted from a molecular arrangement inhibiting intermolecular interactions for quenching the fluorescence state in crystals.     

Synthesis of tricyclic isoindoles and thiazolo[3,2-c][1,3]benzoxazines

The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac₂O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from l-cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The thermolysis of (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazine-3-carboxylic acid in Ac₂O gave 5-acetyl-2-phenyl-2,3-dihydrothiazole. The structures of methyl (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylate 1a and methyl (2R,4R)-N-chlorocarbonyl-2-(2-hydroxyphenyl)thiazolidine-4-carboxylate 9 were determined by X-ray crystallography.     

The n-orbital sequence in 1,3 diazaadamantane

The photoelectron spectra of 1,3-diazaadamantane (1) and 1,3-diaza-6-methyleneadamantane (2) have been measured. An analysis of the spectra based on a ZDO model indicates that the ordering of the n-orbitals in 1 is b₂(n?λσ) above a₁(n₊?λσ). The splitting of b₂ and a₁ in 1 is dominated by the through space interaction. These results are confirmed by semiempirical calculations of the Extended Hückel and MINDO/3 type. An analysis of the PE spectrum of 1,3-diazaadamantanone(6) (5) indicates that in 5 the inductive effect of the CO group is dominant.     

Substituent effects in the ring-chain tautomerism of 1,3-diaryl-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines

Condensation of Betti base analogue amino naphthols with substituted benzaldehydes led to 1,3-diaryl-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines (3-9) which proved to be three-component (r¹-o-r²) tautomeric mixtures in CDCl₃ at 300 K. The electronic effects of the 3-aryl groups on the ratios of the ring-chain tautomeric forms at equilibrium could be described by the equation log K_X=ρσ⁺+log K_X=H. The value of the intercept was found to be strongly influenced by the steric arrangement of the 1,3-diaryl substituents.