Stereochemistry and 13C NMR investigation of 9-halotetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones

It was shown that the halogen atom occupies the quasi-axial position in the predominant conformer of the 9-halo derivatives of tetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones. When R³ = Me, the conformational equilibrium is determined by the latter substituent which is always quasi-axial. The effects of the methyl group and the halogen atoms on the ¹³C chemical shifts (SCS values) were used for the identification of cis and trans isomers. Interesting non additivity of substituent effects was found in derivatives bearing quasi-axial substituents at C-6 and C-9: and this was caused by the ring flattening.     

Studies on inclusion complexes of calix[4]arenes capped by diamide bridges with small organic molecules

The inclusion of small neutral organic guests (acetonitrile, toluene, pyrazine, butylamine, nitromethane) by cyclic calix[4]arene diamide receptors was studied by (1)H NMR spectroscopy. The binding constants determined by (1)H NMR titration, and the results obtained by T(1) relaxation measurements and DOSY confirm the importance of the acidity of the C-H bond of the guests and highlight the role of steric interactions including conformational properties of the receptors in the recognition process.     

Nitrogen-containing carbon nanotubes as solid base catalysts

Nitrogen-containing carbon nanotubes (NCNT) are effective re-usable solid base catalysts, their activity for a Knoevenagel condensation being related to the amount of pyridinic nitrogen incorporated in the NCNT structure, which could be tuned by the synthesis parameters of the catalyst.     

Studies on Calix(aza)crqwns,III. Synthesis of 1,3-Alternate Calix[4]arenes Capped by Diamide Bridges

The akylation of calix[4]arenes 1 capped by diamide bridges gave fully substituted compounds 5 and 6 of 1,3-alternate conformation. Diesters 6 were cyclized with diamines to afford doubly capped derivatives 7.