Single-molecule electronics have attracted a great deal of attention in terms of the bottom-up construction and ultimate miniaturization of electronics. Development of novel materials for this application has become an active area of research. We have designed and synthesized new π-conjugated systems for the use in “anchor” and “insulated molecular wire” units, which are essential components of single-molecule electronics. The tetraphenylmethane-based tripodal structures with anchoring functional groups were developed to function as anchor units, that is, these molecules fulfill not only the electronic communication between electrodes and molecules but also robust attachment to electrodes with controlling the molecular orientation. Structurally well-defined oligothiophenes were utilized as a key framework of molecular wires. The combination of cyclopenta [c] thiohene with orthogonally introduced bulky substituents accomplished the encapsulation of derived oligothiophene backbones without disturbing effective conjugation, leading to the construction of insulated molecular wires.
Biofouling is adverse growth of marine organisms on manmade submersible structures such as ships’ hulls and cause significant economic and environmental problems. As a fouling inhibitor, tributyltin (TBT) has been widely used for controlling the sessile organisms since the early 1960s. Unfortunately, serious pollution of the marine environment due to the deleterious effect of TBT prompted the International Maritime Organization (IMO) to call in 2008 for a ban on the use of tributyltin (TBT) on ships. Since marine invertebrates prevent settlement of other benthic marine organisms through the use of natural substances with antifouling properties without causing serious environmental problems, natural antifouling products with good antifouling properties but without biocidal properties have attracted considerable attention. Among these, 10-isocyano-4-cadinene and omaezallene show promise as lead compounds for the development of new environmentally friendly antifouling agents due to its potent antifouling activity against the cypris larvae of the barnacle Amphibalanus amphitrite and low toxicity. 10-Isocyano-4-cadinene, an isocyanosesquiterpene, was isolated from nudibranchs of the family Phyllidiidae. On the other hand, omaezallene is a bromoallene-containing C15-acetogenin isolated from the red alga Laurencia sp. Herein, we wish to describe our research on the isolations, structure elucidations, total syntheses, and evaluation of the antifouling activities of the natural products and their derivatives. The absolute configurations of the natural products were unambiguously established through our asymmetric total syntheses.
Imines are among the most ubiquitous species in organic and bioorganic chemistry; however, the reactivities of N-alkyl unsaturated imines have not been thoroughly explored due to their instability profiles. We describe the novel reactivity of the N-alkyl-unsaturated imines derived from substituted aldehydes, aminoalcohol or diamine, and paraformaldehyde to produce 2,6,9-triazabicyclo [3.3.1] nonanes, 1,5-diazacyclooctanes, hexahydropyrimidines and 1,3,5-triazacyclooctanes through a formal [4+4], [4+2] and [4+2+2] cycloaddition reaction. When using the chiral aminoalcohol, the iminocycloaddition reaction proceeded in a stereocontrolled manner. The reaction products were successfully transformed via simple functional group manipulations to the variously substituted chiral 1,3-diamines, which could not be simply accessed by the other methods. Furthermore, we synthetically demonstrated that eight-membered heterocycles, namely, 2,6,9-triazabicyclo [3.3.1] nonanes and 1,5-diazacyclooctanes, are the exclusive products of the reaction of acrolein with biologically relevant amines, e.g., polyaimes. These compounds are produced in much higher amounts and efficiencies than the acrolein biomarker in current use. Our results not only indicate that eight-membered heterocycles may potentially be used as new biomarkers, but also strongly suggest the involvement of these heterocycles in various important biological phenomena, e.g., an acrolein-mediated mechanism underlying oxidative stress or inhibitory effects of amyloid peptide fibrillization.
Novel synthesis of chiral polymers containing catalytic active sites is described. Precise control of the chiral polymer structure gives specific chiral microenvironment suitable for an asymmetric catalysis. These polymeric chiral catalysts often show higher enantioselectivities in asymmetric reactions compared with the corresponding original low-molecular-weight catalysts. Many of chiral organocatalysts consist of ionic structure, which act as phase transfer catalysts. Ionic bond formation reaction such as quaternary ammonium sulfonate formation was used for the synthesis of chiral polymers. Typical reaction between chiral bis(quaternary ammonium halide) and disodium disulfonate gives chiral ionic polymers. This simple chiral polymer synthesis enable us to prepare various kinds of polymeric chiral phase transfer catalysts. Cinchona alkaloids and their derivatives have been vigorously developed as excellent chiral catalysts. Polymerization of cinchona derivatives have been described. Not only chiral ionic polymers, chiral polyethers and polythioethers have also been synthesized from cinchona alkaloid. Mizoroki-Heck polymerization of cinchona alkaloid was also established. These cinchona polymers exhibited powerful tool in asymmetric synthesis. Another important organocatalyst is chiral imidazolidinones developed by MacMillan. The polymerization of MacMillan catalysts was investigated. Highly enantioselective MacMillan polymers have been developed. Some chirally modified transition metal catalysts have been polymerized to give chiral polymer catalysts. Asymmetric transfer hydrogenation of imines was demonstrated.
The design of a chiral organocatalyst is very important for achievement of a high optical purity in a catalytic asymmetric reaction. Recently, we developed various chiral β-amino alcohol organocatalysts. These organocatalysts showed high levels of catalytic activity in the asymmetric Diels-Alder (DA) reactions of some dienes with dienophiles and 1,3-dipolar cycloaddition of some nitrones with α,β-unsaturated aldehydes, respectively. Especially, β-amino alcohols worked as organocatalyst in the DA reaction of 1,2-dihydropyridines with acroleins to afford the useful synthetic intermediate of Tamiflu. The review summarizes these our studies.
A nucleophilic amination strategy allows for expeditious access to various N-substituted α-amino carbonyl compounds. However, development of catalytic method remained unexplored in compared to an electrophilic amination strategy. The present review focused on the recent reports of a nucleophilic amination strategy for catalytic synthesis of α-amino carbonyl compounds.