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).     

Androstane alkaloids from musk of Moschus moschiferus

Two androstane alkaloids were isolated from the musk of Moschus moschiferus. The structures were elucidated to be 3alpha-ureido-androst-4-en-17-one (1) and 3alpha-ureido-androst-4-en-17beta-ol (2) by two-dimensional NMR analysis (HMQC, 1H-1H COSY, HMBC, and NOESY).