Aromatic polyketone is one of the most highly performed super engineering plastics With the progress of clarification of the exact feature of structure and thermal behavior of the polymers, a lot of novel aromatic polyketones have appeared and various synthetic approaches were undertaken in these years The recent advances of polyketones are reviewed from synthetic interests. (1) New synthetic reactions, introduction and removal of tentative auxiliary groups in order to maintain the flexibility of polymer chain during chain elongation reaction, and uses of transition metals as a highly effective catalyst were developed for achievement of high-molecular-weight polymer skeleton. (2) Fundamental structural perturbation was undertaken by introduction of crankshaft rings and additional conjugated moieties. (3) Introduction of side groups and their chemical transformation were undertaken to perform new structures and advanced properties. (4) Fine syntheses and reactions of designed oligomers and polymer precursors both for model studies and reactive oligo/polyketones were also investigated. The reports in 1992 and later were mainly surveyed.
The rate-limiting enzyme in the cholesterol biosynthesis has been shown to be 3-hydroxy-3-methylglutarylcoenzyme A reductase (HMG-CoA reductase), which converts HMG-CoA to mevalonic acid. Inhibition of the enzyme is proved to be an effective method for therapeutic intervention in hypercholesterolemia. For example, treatment of atherosclerosis has been convincingly established by recent clinical success of lovastatin, pravastatin, simvastatin or its relative. Accordingly, efforts have been made to discover more potent and better tolerating synthetic analogs, having trans-4-hydroxytetrahydro-2-pyrone ring or its seco acid form 3, 5-dihydroxy-pentanoic acid moiety in common. Although earlier syntheses suffered from low overall yields along with many steps and low selectivity, efficient and highly stereoselective syntheses have been developed last few years. Herein is reviewed recent progress in synthetic efforts of HMG-CoA reductase inhibitor with the emphasis on (1) connection of an aryl unit with the mevalonic acid moiety through multistep synthesis, Wittig-Horner-Emmons reaction, elimination reaction, or cross-coupling reaction and (2) synthesis of optically active lactone moiety by optical resolution, asymmetric reaction, or use of a chiral synthon.
New sigmatropic and intermolecular hydrogen-bonded liquid crystals with a tropone core such as 2- (4-alkoxybenzoyloxy) -5-alkoxytropones, 2- (4-alkoxybenzyloxy) -5-alkoxytropones, 2-acyloxy-5-alkoxytropones, 2, 5-diacyloxytropones, 2- (2-alkenyloxy) -5-alkoxytropones, 5-alkylamino-2- (4-alkoxybenzoyloxy) tropones, and 5-alkoxy-2- (4-alkylaminobenzoyloxy) tropones were prepared to evaluate their properties. Although the fact that the tropone ring is wider than the benzene ring should predict an inferior thermal stability for the troponoid mesophase, this was not the case as the tropone carbonyl group played important roles when these compounds exhibit mesophases ; it worked as an accepter of an intramolecular acyl migration, a polar lateral substituent, and an accepter of an intermolecular hydrogen bond. These behaviors are solely characteristic of troponoids.
Maitotoxin was first discovered as one of the causative toxins responsible for ciguatera, which is a form of seafood poisoning prevalent in coral reef area. The structure (1) has been elucidated to be a polyketide compound with a molecular weight of 3422 Da, which makes the toxin the largest natural non-biopolymer known to date. The structure is partly reminiscent of brevetoxins or ciguatoxins, which comprise trans-fused polycyclic ethers, though maitotoxin possesses about three times as many ether rings as does brevetoxin B. In this paper we review the structure elucidation of maitotoxin with the main focus on spectroscopic methodology, particularly on tandem mass spectrometry (MS/ MS), three-dimensional NMR spectra, and stereostructural analysis using NOE and 3J/H.H data coupled with force field calculations. Collisionally Activated Dissociation (CAD) MS/MS spectra with a negative FAB ionization were successfully measured for fragment B (MW. 2328 Da) of maitotoxin and revealed fragment ions from which the sizes and sequences of ether rings easily were derived. Three dimensional NOESY-HMQC with pulse field gradient was determined for a 13C-enriched specimen (at about 4%) and provided 64 13C-edited NOESY spectra, some of which brought essential NOE information regarding the mode of ether cyclization and stereochemistry.
This paper describes the reaction of phosphorus ylides with chalcogen compounds. Thioaldehydes were formed by the reaction of phosphorus ylides with thiirane or elemental sulfur, which further reacted with dienes to afford the corresponding cycloadducts. Thioaldehydes were also found to react with secondary amines to give the corresponding thioamides. 4, 4′-Dimethoxy-and 4, 4′-dimethylselenobenzophenone could be isolated in moderate yields by the reaction of diarylmethylenetriphenylphosphoranes with elemental selenium in toluene at 90°C. Attempted isolation of unsubstituted selenobenzophenone afforded only its dimer. The oxidation and thiation of 4, 4′-dimethoxyselenobenzophenone afforded the corresponding benzophenone and thiobenzophenone in good yields. The reaction of selenobenzophenone with cyclopentadiene afforded the corresponding cycloadducts (3, 3-diary1-2-selenabicyclo [2.2.1] hept-5-ene), whereas bicyclic diselenides (4, 4-diary1-2, 3-diselenabi-cyclo [3.3.0] oct-7-ene) were obtained by using excess selenium and higher temperature. The reaction of 4, 4′-dimethoxyselenobenzophenone with benzenediazonium carboxylate afforded 2, 2-di (4-methoxyphenyl) benzo-1, 3-oxaselenane. Other reactions were also described.