Comparison of photomacrocyclization reactions of trimethylsilyl- and tributylstannyl-terminated phthalimido- and maleimido-polyethers

SET-promoted photomacrocyclization reactions of trimethylsilyl- and tributylstannyl-terminated phthalimido- and maleimido-polyethers were investigated. The results indicate that the excited state cyclization processes, which take place via sequential SET-destannation pathways, produce macrocyclic polyethers more efficiently than those involving sequential SET-desilylation routes do. In addition, differences in product distributions obtained from photoreactions of trimethylsilyl- and tributylstannyl-terminated maleimido-polylethers suggest that more than one mechanistic pathway is followed in excited-state reactions of the tin-containing substrates.     

New synthetic method of o,s-thioacetals of formylphosphonates

The reaction of diethyl [(methylthio or arylthio)methyl]phosphonate with N-chlorosuccinimide (NCS) affords (α-chloromethanephosphonate(5), which can be converted into a variety of O,S-thioacetals of formylphosphonates(2) by reaction with alcohols.     

Dimeric compounds containing malonic acid as the central linking unit: synthesis and mesomorphic properties

Eight new dimeric compounds containing malonic acid as the central linking unit (series M- n - X ) have been synthesized and their mesomorphic properties studied. All these compounds are found to be liquid crystalline, forming mainly nematic and smectic phases. We have carried out microscopic textural observations, X-ray diffractometry as well as solid state NMR studies on these compounds.     

An optimized multislice acquisition sequence for the inversion-recovery MR imaging

An optimized multislice data acquisition scheme for inversion-recovery MR imaging is proposed and experimental results are presented. In this new scheme, instead of forming a set of multislice inversion-recovery sequences in series for a given phase encoding step, 180° inversion pulses corresponding to different slices are interwoven with the spin echo data acquisition sequence in an optimal way depending on the desired inversion-recovery time. For example, between the 180° inversion RF pulse and the spin-echo imaging sequence, a number of imaging and inversion sequences are inserted with different slice combinations, i.e., long inversion-recovery time is effectively utilized for the other slice pre-inversion and data acquisition. With the optimized sequence, imaging time has been reduced by as much as a factor of four compared with the existing methods.     

Phenylenedioxydiacetamide—End group effect

A series of neutral ligands featuring ether and amide groups were prepared. The complexation studies suggest a strong participation of the extra terminal amide group.Taken in part from the Master's Thesis of Antonio Paulo Altoé, Instituto Militar de Engenharia, Rio de Janeiro, Brasil (1979).