On treatment of alkyl aryl sulfoxides with alkylmetals (alkyllithium or Grignard reagent) sulfuralkyl or sulfur-aryl bond-cleavage takes place to give new alkylmetals or arylmetals. This reaction is called sulfoxide-metal exchange reaction. In this paper, the author mainly reviews the new methods for the generation of magnesium carbenoids and alkylmagnesiums having a heteroatom on their a-position by the sulfoxide-magnesium exchange reaction. When the alkyl aryl sulfoxides have a heteroatom (such as Cl, O, N) on the α-position in the alkyl group, the reaction with alkylmetals results in the sulfur-alkyl bond cleavage to give a carbenoids and/or α-heteroatom-substituted carbanions at low temperature in high yields. Especially, magnesium carbenoids are quite interesting compounds and some novel synthetic reactions have been developed via the carbenoids. The sulfoxide-magnesium exchange reaction of sulfinylaziridines gave the stable aziridinylmagnesiums, from which a new synthesis of both enantiomers of the optically active amines having a quaternary chiral center was realized. A new synthesis of olefins and allenes, including optically active form, from sulfoxides and alkenyl sulfoxides, and carbonyl compounds by the sulfoxide-magnesium exchange reaction is also reviewed.
The reaction of 3-chloro-2-chloromethyl-l-propene with 2 equimolar phenolic compounds gave isobutenyl bis (aryl) ether compounds. The thermal or Lewis acid-assisted Claisen rearrangement of the ether compounds results in generating phenolic compounds having plural hydroxyl groups at one step reaction. We named this reaction as “tandem Claisen rearrangement, ” where the Claisen rearrangement successively occurs two times at each isobutenyl ether moiety. This reaction can be applied not only to acyclic, but also to macrocyclic compounds having isobutenyl ether moiety. Tetradentate ligands with two quinolinol moieties, tripodal hexadentate ligands with either three quinolinol or catechol moieties, etc. have been synthesized as acyclic rearranged products. As macrocyclic rearranged products, various kinds of novel crownophane and cyclophane derivatives having plural hydroxyl groups have been synthesized. These compounds prepared via tandem Claisen rearrangement have been found to be able to work as ionophore, fluorophore, host molecules for neutral organic molecules, chiral ones, ligands for transition metal ions and so on.
This review describes our recent results on rhodium-catalyzed carbon-carbon bond forming reactions. We have developed two types of multi-component coupling starting from the oxidative addition of a hydrosilane to a low-valent rhodium complex. One type is followed by the insertion of α, β-unsaturated carbonyl compounds into the resultant Rh-H bond to give a rhodium enolate intermediate which shows sufficient nucleophilicity toward aldehydes, aldimines, isocyanates, and allylic alcohol derivatives to form coupling products. The other type includes the insertion step of alkynes into the Rh-Si bond. This sequence is relayed to silylformylation of an acetylenic bond, selective formation of 2-silylmethylalkenals, silylative lactonization of alkynylalcohols, silylative lactamization of alkynylamines, silylative bicyclocarbonylation of 1, 6-diynes, and transannular silylformylation of 1, 6-enynes under CO pressure (20 atm).
Rearrangements of 1, 2-epoxy alcohol derivatives having electron-withdrawing protective groups such as acyl or sulfonyl group have been developed leading to the asymmetric construction of chiral quaternary carbon centers and spiro centers. The success of the novel rearrangements here depends on the electron-withdrawing property of the protective groups. The methods were applied to the asymmetric syntheses of several natural products such as fredericamycin A, (+) - (S) -sporochnol A, (-) -aphanorphine, and (-) -a-herbertenol.
Recent development in the use of high-precision quantum chemical calculations for the investigation of the mechanisms of synthetically important organometallic reaction is reviewed. The review is focused on the following issues that have be the subject of much discussion in the society of synthetic organic chemists for many years : (1) Nucleophilic addition to carbonyl compounds, (2) osmium-tetraoxide-catalyzed dihydroxylation, (3) organocopper reactions, and (4) Simmons-Smith cyclopropanation.
The myxomycetes (true slime molds) are an unusual group of primitive organisms that may be assigned to one of the lowest classes of eukaryotes. As their fruit bodies are very small and it is very difficult to collect much quantity of slime molds, few studies have been made on the chemistry of myxomycetes. Cultivation of the plasmodium of myxomycetes in a practical scale for natural products chemistry studies is known only for very limited species such as Physarum polycephalum. We recently studied the laboratory-cultivation of myxomycetes and several species have been successfully cultured in agar plates. Chemical constituents of cultured plasmodia of several species of myxomycetes of the genera Didymium and Physarum were examined to obtain several sterols, new lipid, or pyrroloiminoquinone derivatives. Studies on the chemical constituents of the field-collected myxomycetes as well as synthetic studies of myxomycetes metabolites by other groups are also described here.