Unique charge-separated pyridinium-barbituric acid zwitterions

A synthetic procedure for the preparation of the unusual charge-separated pyridinium barbiturate zwitterion 2 from 1,3-dimethylbarbituric acid and 2-pyridinecarbaldehyde in methanol was developed. The structure of the compound was confirmed with X-ray analysis to demonstrate the strong charge separation throughout the molecule. One would expect that this charge separation would increase its reactivity; however, contrary to this expectation, the compound is very stable in acidic media, and in the presence of a base, decarbonylation occurs on one barbituric acid while the zwitterionic moiety of the molecule stays intact.     

A study of oligoprenyl coupling reactions with allylic stannanes

All-E or E,Z,E-oligoprenols may be synthesized from allylic stannanes by reaction with prenyl aldehydes. [reaction: see text]     

Intersecting all edges of centrally symmetric polyhedra by planes

A1 least three planes are needed in order to cut all edges of a 3-dimensional centrally symmetric convex polytope by planes which miss all vertices of the polytope. In contrast, there exist centrally symmetric convex tessellations of the 2-sphere for which two planes are sufficient.     

über die Darstellung von kondensierten Azolo-[1,2,4]-triazinen aus heterocyclischen Diazoverbindungen

Diazotized 3-amino-1,2,4-triazole reacted with 1,3-cyclohexanedione or its 5,5-dimethyl derivative to give the tricyclic 1,2,4-triazine derivatives1 a and1 b. With 1,3-indanedione the tetracyclic compound8 was obtained. Compound1 a or the diacetyl derivative4 a are transformed in an acid catalyzed reaction into the fully aromatic system6 a with simultaneous rearrangement. Chemical reductions of systems1, 10 and12 have been investigated and the compounds9, 11 and13 were isolated and identified. Diazotized 2-aminothiazole readily formed the coupling products with reactive methylene compounds, but only14 could be prepared pure by cyclodehydration.     

Complexation of metals with piperazine-containing azamacrocyclic fluorophores

Azamacrocyclic fluorophores containing piperazine units were synthesized using sequential rhodium-catalyzed regioselective hydroformylation-reductive amination. A piperazine unit is introduced into the macrocycles to act simultaneously as electron donor and binding site. The macrocycles chelate divalent cations, either Zn2+ or Co2+, which considerably enhanced fluorescence. Complexation with Zn2+ was additionally confirmed by NMR.     

Synthesis of (S)‐3‐heteroaryl‐2‐hydroxy‐l‐propyl benzoates by ‘ring switching’ methodology

(S)‐5‐Benzoyloxymethyl‐3‐[(E)‐(dimethylamino)methylidene]tetrahydrofuran‐2‐one (6), prepared in 5 steps from L‐glutamic acid (1), was used as precursor in a one step ‘ring switching’ synthesis of (S)‐2‐hydroxy‐3‐heteroaryl‐l‐propyl benzoates 13‐18, 23, 24. In the reaction of 6 with 2‐aminopyridine (21) and 2‐amino‐4,6‐dimethylpyrimidine (22) the corresponding dimethylamine substitution products (25, 26) were obtained.     

Heats of formation of C(6)H(5)(•), C(6)H(5)(+), and C(6)H(5)NO by threshold photoelectron photoion coincidence and active thermochemical tables analysis

Threshold photoelectron photoion coincidence has been used to prepare selected internal energy distributions of nitrosobenzene ions [C(6)H(5)NO(+)]. Dissociation to C(6)H(5)(+) + NO products was measured over a range of internal energies and rate constants from 10(3) to 10(7) s(-1) and fitted with the statistical theory of unimolecular decay. A 0 K dissociative photoionization onset energy of 10.607 ± 0.020 eV was derived by using the simplified statistical adiabatic channel model. The thermochemical network of Active Thermochemical Tables (ATcT) was expanded to include phenyl and phenylium, as well as nitrosobenzene. The current ATcT heats of formation of these three species at 0 K (298.15 K) are 350.6 (337.3) ± 0.6, 1148.7 (1136.8) ± 1.0, and 215.6 (198.6) ± 1.5 kJ mol(-1), respectively. The resulting adiabatic ionization energy of phenyl is 8.272 ± 0.010 eV. The new ATcT thermochemistry for phenyl entails a 0 K (298.15 K) C-H bond dissociation enthalpy of benzene of 465.9 (472.1) ± 0.6 kJ mol(-1). Several related thermochemical quantities from ATcT, including the current enthalpies of formation of benzene, monohalobenzenes, and their ions, as well as interim ATcT values for the constituent atoms, are also given.