The dimer,trimer and 1,2,4‐tri­thiol­ane of adamantane­thione

The mol­ecules of di­spiro­[1,3‐dithietane‐2,2′:4,2′′‐diadamantane], C₂₀H₂₈S₂, have crystallographic C_i symmetry, as well as local D_2h symmetry, and a planar 1,3‐dithietane ring. The mol­ecules of tri­spiro­[1,3,5‐tri­thia­ne‐2,2′:4,2′′:6,2′′′‐triadamantane], C₃₀H₄₂S₃, have approximate C₂ symmetry and the 1,3,5‐tri­thia­ne ring has a twist–boat conformation. The C—S—C bond angles within the ring are about 8° larger than observed in most related 1,3,5‐tri­thia­ne structures. In di­spiro­[1,2,4‐tri­thiol­ane‐3,2′:5,2′′‐diadamantane], C₂₀H₂₈S₃, the mol­ecules have local C₂ symmetry and the 1,2,4‐tri­thiol­ane ring has a half‐chair conformation.     

A new interpretation of chlorine leaving group kinetic isotope effects; a theoretical approach

The chlorine leaving group kinetic isotope effects (KIEs) for the S(N)2 reactions between methyl chloride and a wide range of anionic, neutral, and radical anion nucleophiles were calculated in the gas phase and, in several cases, using a continuum solvent model. In contrast to the expected linear dependence of the chlorine KIEs on the C(alpha)-Cl bond order in the transition state, the KIEs fell in a very small range (1.0056-1.0091), even though the C(alpha)-Cl transition state bond orders varied widely from approximately 0.32 to 0.78, a range from reactant-like to very product-like. This renders chlorine KIEs, and possibly other leaving-group KIEs, less useful for studies of reaction mechanisms than commonly assumed. A partial explanation for this unexpected relationship between the C(alpha)-Cl transition state bond order and the magnitude of the chlorine KIE is presented.     

Thermal decomposition of cadmium succinate dihydrate

Thermal decomposition of cadmium succinate dihydrate, CdC₄H₄O₄·2H₂O, was studied in dynamic helium and air atmospheres by means of simultaneous TG, DTA and MS analysis. It was found that dehydration of CdC₄H₄O₄·2H₂O takes place in the temperature range 80–165°C and at low heating rates formation of monohydrate was stated. The anhydrous cadmium succinate decomposes at about 350°C to metallic cadmium. The gaseous products of cadmium succinate decomposition are CO₂ and H₂O. Formation of small amounts of 3-phenylpropanal and 1,7-octadiene during decomposition in helium was revealed. In helium cadmium evaporates at the temperature of decomposition and the residue consists of small amount of elementary carbon formed in result of pyrolysis of succinate groups. In air cadmium oxidizes and the final solid product of decomposition is CdO.     

Nitroaldol-reaction of aldehydes in the presence of non-activated Mg:Al 2:1 hydrotalcite; a possible new mechanism for the formation of 2-aryl-1,3-dinitropropanes

Commercially available, non-activated 2:1 Mg:Al hydrotalcite catalyzes the nitroaldol reaction between a variety of aromatic and aliphatic aldehydes and simple nitroalkanes such as nitromethane and nitroethane. A new mechanism is proposed for the formation of the 1,3-dinitropropanes. The threo/erythro diastereoselectivity of the nitroethane-adducts was determined by ¹H NMR spectroscopy and was found to range from 50:50 to 70:30. The substituents of the aromatic aldehydes influenced the isomer ratio.     

Coulomb-assisted dissociative electron attachment: application to a model peptide

The fragmentation of positively charged gas-phase samples of peptides is used to infer the primary structure of such molecules. In electron capture dissociation (ECD) experiments, very low-energy electrons attach to the sample and rupture bonds to effect the fragmentation. It turns out that ECD fragmentation tends to produce cleavage of very specific types of bonds. In earlier works by this group, it has been suggested that the presence of positive charges produces stabilizing Coulomb potentials that allow low-energy electrons to exothermically attach to sigma orbitals of certain bonds and thus to cleave those bonds. In the present effort, the stabilizing effects of Coulomb potentials due to proximal positive charges are examined for a small model peptide molecule that contains a wide range of bond types. Direct attachment of an electron to the sigma orbitals of eight different bonds as well as indirect sigma bond cleavage, in which an electron first binds to a carbonyl C=O pi orbital, are examined using ab initio methods. It is found that direct attachment to and subsequent cleavage of any of the eight sigma bonds is not likely except for highly positively charged samples. It is also found that attachment to a C=O pi orbital followed by cleavage of the nitrogen-to-alpha-carbon bond is the most likely outcome. Interestingly, this bond cleavage is the one that is seen most commonly in ECD experiments. So, the results presented here seem to offer good insight into one aspect of the ECD process, and they provide a means by which one can estimate (on the basis of a simple Coulomb energy formula) which bonds may be susceptible to cleavage by low-energy electron attachment.     

Stopped-flow determination of 2-mercaptopyrimidines as inductors of the iodine-azide reaction

A stopped-flow method for the determination of 2-mercaptopyrimidine and its 14 derivatives by the iodine-azide has been elaborated. Spectrophotometric detection was applied and the decrease in the absorbance of the iodine-starch complex was monitored at 595 nm within 5 s. The effect of the concentration of the reagents on the rate of the reaction was investigated and a kinetic method for determination of compounds is proposed. 2-Mercaptopyrimidines can be determined at 10⁻⁶ to 10⁻⁵ mol L⁻¹ level and the relative standard deviation is below 1%. The elaborated method has been applied to the determination of 6-methyl- and 6-propyl-2-thiouracil in drugs.     

Complexes of bivalent metal cations in electrospray mass spectra of common organic compounds

In the standard electrospray ionization mass spectra of many common, low molecular mass organic compounds dissolved in methanol, peaks corresponding to ions with formula [3M + Met](2+) (M = organic molecule, Met = bivalent metal cation) are observed, sometimes with significant abundances. The most common are ions containing Mg(2+), Ca(2+) and Fe(2+). Their presence can be easily rationalized on the basis of typical organic reaction work-up procedures. The formation of [3M + Met](2+) ions has been studied using N-FMOC-proline methyl ester as a model organic ligand and Mg(2+), Ca(2+), Sr(2+), Ba(2+), Fe(2+), Ni(2+), Mn(2+), Co(2+) and Zn(2+) chlorides or acetates as the sources of bivalent cation. It was found that all ions studied form [3M + Met](2+) complexes with N-FMOC-proline methyl ester, some of them at very low concentrations. Transition metal cations generally show higher complexation activity in comparison with alkaline earth metal cations. They are also more specific in the formation of [3M + Met](2+) complexes. In the case of alkaline earth metal cations [2M + Met](2+) and [4M + Met](2+) complex ions are also observed. It has been found that [3M + Met](2+) complex ions undergo specific fragmentation at relatively low energy, yielding fluorenylmethyl cation as a major product. [M + Na](+) ions are much more stable and their fragmentation is not as specific.     

Intramolecular hydrogen bonds in crystals of thiophosphorylbenzopyrane derivatives – X-ray and FT-IR studies

The crystal structures of two new benzopyrane derivatives are analyzed and compared with previous X-ray investigations on related compounds. A particular attention is focused on intramolecular interactions. For the chromone derivatives (1 and 3) only one kind of interaction is possible, i.e., N–HO, whereas for the coumarine derivatives (2 and 4) two types of intramolecular hydrogen bonding are observed – N–HO and O–HN. Two types of H-bond for coumarine derivatives are the result of the existence of two tautomeric forms – enamine and iminoenol. Combined spectroscopic, NMR and IR measurements confirm such tautomeric equilibrium in solution. The influence of the additional intermolecular hydrogen bonds on the stabilization of tautomeric forms in crystals is also discussed here.     

A benzopyran derivative substituted at position 3

In (E)‐3‐{[(di­phenoxy­phospho­ryl)­methyl­hydrazono]­methyl}‐4H‐1‐benzo­pyran‐4‐one, C₂₃H₁₉N₂O₅P, the benzo­pyran–methyl­hydrazone moiety is planar and the two phenoxy phenyl rings are inclined at angles of 21.29 (6) and 89.33 (5)°. Weak C—H?O and C—H?N intramolecular interactions exert some influence on the planarity and orientation of that moiety.     

A three-component reaction for diversity-oriented synthesis of polysubstituted piperidines: solution and solid-phase optimization of the first tandem aza[4+2]/allylboration

This article describes the design and optimization of a simple three-component aza[4+2]/allylboration reaction to access polysubstituted alpha-hydroxyalkyl piperidines in a highly diastereocontrolled fashion from maleimides, 4-boronohydrazonodienes, and aldehydes. The aldehyde component does not interfere with the first aza[4+2] step, and it was found that this tandem reaction provides better yields of piperidine products 5 when carried out in one-pot. The required 4-borono-hydrazonodienes 1 are synthesized efficiently from the condensation of 3-boronoacrolein pinacol ester (4) with hydrazines. Overall, the three-component process using N-substituted maleimides as dienophiles produces four stereogenic centers and is quite general. It tolerates the use of a wide variety of aldehydes and hydrazine precursors with different electronic and steric characteristics. By allowing such a wide substrate scope and up to four elements of diversity, this reaction process is particularly well adapted towards applications in diversity-oriented synthesis of polysubstituted piperidine derivatives. The suitability of the aza[4+2]/allylboration reaction for use in solid-phase chemistry was also demonstrated using a N-arylmaleidobenzoic acid functionalized resin. This novel multicomponent reaction thus offers a high level of stereocontrol and versatility in the preparation of densely functionalized nitrogen heterocycles.