Mass spectral study of differently substituted 2-oxo- and 2-thioxo-1,3,4-benzotriazepines

The mass spectra of seven 2-thioxo- and four 2-oxo-1,3,4-benzotriazepines were recorded under electron ionization, and the fragmentation patterns were elucidated by exact mass measurement and metastable ion analysis. Some variations in the nature and position of the substituents greatly affected the mass spectra, allowing easy differentiation of isomeric compounds. The most characteristic feature of the mass spectral behavior of the compounds was the large number of ring contraction and complicated rearrangement reactions.     

Electron impact induced fragmentation of dihydro-1,4-dithiines. 2,3-Substituted 5,6-dihydro-l,4-dithiines

In the electron impact induced fragmentation of 2,3-disubstituted 5,6-dihydro-1,4-dithiines, the most important cleavage of the heterocyclic ring occurs via the retro-Diels-Alder type of reaction. The further fragmentation of the resulting radical cation gives rise to substitutes thiocarbonyl cations. This fragmentation favours formations of ions in which the electron-deficient carbon-sulphur triple bond is stabilized by an electron-releasing group. The ring fragmentation was observed to be dependent on the nature of the 3- and 2-substituents of the ring when a series of 3- and 2-substituted 5,6-dihydro-l,4-dithiines was investigated. The fragmentation of dihydro-l,4-dithiines partly resembles the fragmentation of the corresponding dihydro-l,4-oxathiines. The presence of the two sulphur atoms in dihydro-l,4-dithiines give rise to more stable molecular ions than observed in the case of the dihydro-1,4-oxathiine analogues. Fragmentations of dihydro-l,4-dithiines can also involve extrusions of alkylradicals or HS-radical from the heterocyclic rings of molecular ions.     

Alkali metal mediated resorcarene capsules: an ESI-FTICRMS study on gas-phase structure and cation binding of tetraethyl resorcarene and its per-methylated derivative

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) with additional ab initio calculations were used to examine the alkali metal cation binding selectivity (i.e., molecular recognition) and host properties of tetraethyl resorcarene (1) and its per-methylated derivative (2). The significance of intramolecular hydrogen bonding for the crown conformation was demonstrated. The presence of intramolecular flip-flop hydrogen bonding in 1 was confirmed both with calculations and in ND3-exchange experiments. All the alkali metal cations formed host-guest complexes by docking inside the cavity of the host. Complexation with the larger cations, especially Cs+, was favored. All the alkali metal cations also formed dimeric resorcarene capsules with 1. The capsules were directly H-bonded species, with no linking solvent molecules. ND3-exchange experiments and molecular modeling revealed the significance of direct intermolecular H-bonding for the crown conformation of 1 and stability of the capsule structure.     

The formation of complexes by tetraethylresorcarene with planar guest ions studied by electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry

Resorcarenes have become a popular subject of study in the field of supramolecular chemistry. In this work the formation of host-guest complexes between a synthetic macrocyclic host, tetraethylresorcarene, and various eligible planar guests, was studied by mass spectrometric methods. The size and nature of the guest ion strongly influenced the complex formation. Collision-induced dissociation experiments revealed the fragmentation patterns of the resorcarene skeleton and the differences in fragmentation induced by the guest ions.     

Electron impact ionization mass spectra of some substituted dipyrido[1,2-a:4,3-d]pyrimidinones

The electron impact ionization mass spectra of dipyrido [1,2-a:4,3-d]pyrimidinones are strongly influenced by the degree of aromaticity of the fused rings. The molecular ions of the compounds are fairly stable. The main routes of fragmentation involve formation of the [M – H]⁺ ion and loss of substituents, H₂CN˙, CO and alkyl radicals.     

Mass spectrometric investigation of noncovalent complexation between a tetratosylated resorcarene and alkyl ammonium ions

Noncovalent complexation between tetratosylated tetraethyl resorcarene (1) and primary, secondary, and tertiary alkyl ammonium ions (mMe, dMe, tMe, mEt, dEt, tEt, dBu, and dHex) was studied by electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry. Interactions of the noncovalent complexes were investigated by means of competition experiments, collision-induced dissociation (CID) experiments, ion-molecule reactions with tripropylamine and gas phase H/D-exchange reactions with deuteroammonia. Gas phase ion-molecule reactions gave especially valuable information about the structure and properties of the complexes. Resorcarene 1 formed relatively stable 1:1 complexes with all aliphatic alkyl ammonium ions. Steric properties of the alkyl ammonium ions and proton affinities of the conjugate amines noticeably affected the complexation properties, indicating the importance of hydrogen bonding in these complexes. According to the competition experiments, the thermodynamically most stable host-guest complexes were formed with alkyl ammonium ions that were most substituted and had the longest alkyl chains. In CID experiments, release of an intact free guest ion or dissociation of the host was observed to depend on the proton affinity of the amine and the strength of the hydrogen bond that was formed. In ion-molecule reactions with tripropylamine, a guest exchange reaction occurred with all alkyl ammonium ion complexes with reaction rates mostly dependent on the steric properties of the original guest ion. In H/D-exchange reactions the N-H hydrogen atoms of the guest ion were exchanged with deuterium, whereas the resorcinol hydrogen atoms remained unchanged.     

Mass spectrometric studies on pyridine-piperazine-containing ligands and their complexes with transition metals formed in solution

Electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) methods were used to study open-chain piperazine-containing ligands (L) and their complexes formed with transition-metal salts. ESI and MALDI measurements were performed with a Fourier transform ion cyclotron resonance (FT-ICR) and a time-of-flight (TOF) mass spectrometer, respectively. Only singly charged complexes, between one ligand and one or several metal ions, were formed in the ESI measurements. Because the net charge was always one, one or several counterions were attached to the complex. Under ESI conditions, the complexes formed between the ligands and metal (Co, Ni, Cu, and Cd) salts were [L + M + X](+), [L + H + M + X(2)](+) and [L + M(2) + X(3)](+) (M = metal ion, X = counterion). In collision induced dissociation reactions the [L + H + M + X(2)](+) complexes easily eliminated one proton and one counterion. Fragmentation pathways were more dependent on the metal ion than the ligand, and elimination of the second counterion occurred with one proton from copper and nickel complexes and with one proton and one hydrogen from cobalt complexes. Differences in the fragmentation of the complexes could be due to electronic configuration of the metal ion. In the MALDI measurements the ratio between the [L + H](+) and [L - H](+) ions varied with the matrix. Fragmentation of the ligands through elimination of 2-methylpyridine end groups occurred with the aromatic matrices containing carboxylic acid and hydroxyl substituents. Ionization of the complexes was not successful with MALDI as the matrix molecules were also attached to the complexes.     

Electron impact and ammonia chemical ionization mass spectra of n-azabicyclo[m.2.0]alkan-(n + 1)-ones (m = 3–6, n = 6–9)

Electron impact induced fragmentation of the title compounds obeys a route where the lactam moiety, OCNH, is cleaved first, with the accompanying formation of a cycloalkene ion. This can be verified by low-resolution, high-resolution, B/E and B²/E spectra as well as by collisional activation spectra of, for example, the ions m/z 82 and 67 from 7-azabicyclo[4.2.0]octan-8-one and from cyclohexene. The only, and fairly weak, fragment ions including O and N are [C₃H₃O]+, [C_kH_2k-2N]⁺ (k = 5–8) and [C₃H₆N]⁺. The ammonia chemical ionization spectra are also characteristic for all four lactams and show the same dominant ions in all cases, namely [M + 1]⁺, [M + 1 + NH₃]⁺˙ and [2 M + 1]⁺˙.     

Liquid‐phase synthesis of mixture‐based bicyclic β‐lactam libraries

Five sets of 27‐membered combinatorial libraries of alicyclic β‐lactams were prepared via liquid‐phase Ugi 4‐center 3‐component reactions (U‐4C‐3CR) utilizing 3 different cis β‐amino acids, 3 different isonitriles and 5×3 sets of aldehydes. Through combinations of the building blocks of one of these libraries, all of the possible sublibraries were also generated. A few azetidinone derivatives were synthesized individually by parallel synthesis.     

A comparative study on the behaviour of 1,3-diheterocyclopentanes (X = O,O; S,S; O,S) under electron impact. The formation of thioacetyl and thiiranyl cations

The electron-impact-induced mass spectra of 1,3-dioxolane (la), 1,3-dithiolane (2a) and 1,3-oxatbiolane (3a) and their 2-methyl (1b–3b) and 2,2-dimethyl [(CH₃)₂: 1c–3c or (CD₃)₂: 1d–3d] derivatives have been studied in detail to gain further insight into their ion structures and competing reaction pathways with low-resolution, high-resolution, metastable and collision-induced dissociation (CID) techniques. For compounds 1a–1d the most significant reaction is loss of H^˙ and CH₃^˙ by α-cleavage and a subsequent formation of CHO⁺ and C₂H₃O⁺ ions. The [M ? H]⁺ ions from 1a and 1b give a C₂H₃O⁺ ion which does not have the acyl cation structure as shown by their CID spectra. In compounds 3a–3d the sulphur-containing ions predominate, the C₂H₃O⁺ now having the acyl cation structure. 1,3-Dithiolanes (2a–2d) exhibit the most complicated fragmentation patterns. Furthermore the [M ? H]⁺ ion from 2a and [M ? CH₃]⁺ ion from 2b have different structures as well as the [M ? H]⁺ ion from 2b and [M ? CH₃]⁺ ion from 2c, as shown by their CID spectra. This can be utilized to explain why 3a–3c and 2a give principally a thiiranyl cation, whereas 2b gives a mixture of this and the thioacyl cation and 2c practically only the open-chain thioacetyl cation.