Generation and synthetic utilization of highly reactive fluorinated intermediates, which include chemistries of trifluoroacetimidoyl halides, electrochemical activation of fluorinated organic compounds, and chalcogen molecule mediated fluorinations, are discussed. Synthesis of optically active trifluoroalanine via trifluoroacetimidoyl palladium intermediates, generation of trifluoroacetimidoyl radicals, electrochemical synthesis of 2-CF3-benzimidazoles, chemistry of benzeneselenenyl fluoride, and SET process between benzeneselenolate anion and fluorinated alkylhalides are highlight of this overview.
A series of selenothioic acid S-esters and diselenoic acid esters have been synthesized by the following three types of methods : (1) reactions of terminal acetylenes with n-butyllithium, selenium and thiols; (2) reactions of selenoic acid O-methyl esters with aluminum chalcogenolates; (3) reactions of selenothioacetic acid S-esters with aldehydes and/or allylic bromides in the presence of a base. On the basis of synthetic results, the general trends for the relative stability of the esters have been proposed. Among several types of esters, one of the most simple esters, i.e., selenium and sulfur counterparts of acetic acid esters are the most stable. The introduction of aromatic substituents does not necessarily enhance the stability of the esters. Reactions of the esters toward heavy metal salts, such as nickel chloride, zinc iodide, and cadmium acetate, electron deficient alkynes, and reducing agents provided new synthetic methods of a variety of organoselenium compounds.
Historical background of alkene metathesis is briefly reviewed. The introduction of the Schrock Mocarbene complex and the Grubbs Ru-carbene complexes has initiated rapid development of synthetic utility of alkene metathesis. Many functional groups are tolerated without protection in the Mo and Ru catalysed metathesis. Among several synthetic applications of the alkene metathesis, the ring closing metathesis offers an extremely useful method for cyclization to give carbo-and hetero-cyclic compounds from medium to large sizes. A number of naturally occurring macrocyclic compounds have been synthesized in shorter steps by the ring closing metathesis using the Ru complex as key reaction. The alkene metathesis has brought in a dramatic change in synthetic designs of complex cyclic compounds.
Manzamines, β-carboline alkaloids having unique heterocyclic systems from marine sponges, are of considerable current interest as compounds generated through unprecedented biosynthetic path or as a challenging target for total synthesis. Recently many manzamine-related alkaloids have been isolated from marine sponges, indicating the unique biogenetic path of manzamines.
Determination of significantly populated conformers in an extremely flexible molecule such as macrocycles is a matter of long standing interest. We have developed a useful and very reliable method for the conformational analysis using a combination of molecular mechanics calculations and chemical shift simulation method. The method utilizes the calculation of the change in chemical shift of a proton produced by nearby substituents. The induced chemical shifts due to anisotropy effect of aromatic ring have been proven to be a useful geometrical probe of structures. Examples of the successful conformational analysis for macrocyclophane and supramolecular complexes of calixarenes with apolar guests including C60 and C70 are presented.
For understanding the interactions between marine organisms, we focused on larval settlement (attachment and metamorphosis) of sessile marine organisms, where chemical substances (chemical signals) play important roles. Here we report firstly the settlement inhibiting substances against barnacles (Balanus amphitrite). More than 300 marine invertebrates were screened for antifouling activity, and more than 60 antifouling compounds including almost 30 new ones were obtained. Some of these compounds [especially with isocyanide, isothiocyanate, and/or formamide group (s)] show strong antifouling activity without toxicity at the very low concentrations. Secondly, we report the metamorphosis inducing substances for ascidians (mainly Halocynthia roretzi). Almost 40 compounds which induce/promote larval metamorphosis were obtained from marine organisms. The real cue for metamorphosis has been isolated from conspecific conditioned water and identified as lumichrome.