In this review we describe syntheses, structures, electronic states, physical properties, reactivities, and functionalities of the compounds which contain metalladichalcogenolene rings consisting from one transition metal atom, two chalcogen atoms, and two unsaturated carbon atoms. The ring shows characteristic reactivities mainly at the metal-chalcogen bond and undergoes some characteristic addition reactions with diazo compounds, quadricyclane, dimethyl acetylenedicarboxylate etc. The reactions of the addition products are also described.

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Various cyclic polysulfides, especially cyclic polysulfides bearing many sulfur-sulfur linkages such as benzopentathiepins, 5H-benzo [f] -1, 2, 3, 4-tetrathiepin, and 4, 8-dialkylbenzo [1, 2-d; 4, 5-d'] bis [1, 2, 3] trithioles, were efficiently synthesized by treating 1, 2- benzenedithiols and related compounds with elemental sulfur in liquid ammonia. The reaction of these cyclic polysulfides with olefins or active methylene compounds under acidic or basic conditions gave some interesting heterocyclic compounds. In this review, details of these reactions are described and versatility of cyclic polysulfides as useful reagents for synthesis of sulfur-containing heterocyclic compounds is emphasized.

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2, 3-Dimethylbutene-2 (DMB-2) is a key olefin for the synthesis of Danitol®, which is a high perfomance pyrethroid insecticide invented by Sumitomo in 1976. At that time, DMB-2 was too expensive for the development of Danitol®. Therefore, we studied the simplest way to DMB-2, that is, the dimerization of propylene to DMB-1 followed by isomerization to DMB-2, and succeeded in developing the efficient dimerization catalyst. This catalyst consists of six components ; nickel naphthenate (Ni (naph)₂) /PR₃/diene/AlEt₃/chlorinated phenol/ H₂O. The characteristics of this catalyst are as follows. (1) The content of DMBS in dimers (DMBS selectivity) is high as 86%. (2) DMB-1 and DMB-2 can be produced at will only by controlling the molar ratio of catalyst components. (3) A small amount of water enhances the catalytic activity remarkably. Using this catalyst, we started the commercial production of DMB-2 in 1983.

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This article describes new methods to introduce a variety of substituents into the α, β or γ position of a piperidine ring by utilizing anodic oxidation as a key reaction. The following patterns of anodic oxidation were exploited to activate the α and, β positions of N-methoxycarbonylpiperidines A; (1) anodic oxidation of A in methanol containing Et₄NOTs to give the α-methoxylated products B, (2) anodic oxidation of A in acetic acid to give the a, /9-bisacetoxylated products C, (3) anodic oxidation of A to afford β-halogenated α-hydroxy-or α-methoxy-piperidine derivatives D, and (4) anodic decarboxylation of pipecolinic acid derivatives to afford B or C. The γ- position of A was activated by converting B or D into β, γ-unsaturated a-methoxypiperidine derivatives E. The activated compounds B, C, D and E were used as useful precursors to introduce substituents into the desired positions of piperidine ring, and some alkaloids containing a piperidine skeleton such as coniine, optically active N-methylconiine, conhydrine, and eburnamonine were synthesized from these precursors.

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The studies on the chemistry of mitomycins are described : i) identification and structural elucidation of mitomycins D, E, F, G, I, J, K, L, M, albomitomycin A, and isomitomycin A from the fermentation broth; ii) derivation of mitomycins structurally close to naturally occurring mitomycins; iii) mitomycin rearrangement, the interconversion between mitomycin A, albomitomycin A, and isomitomycin A;iv) chemical con-version of isomitomycin A from mitomycin A; v) 3α-alkoxymitomycins, unexpected by-products in decarbamoylation of mitomycins;vi) the configuration of mitiromycin.

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Highly selective cross-coupling reaction of organosilanes with organic halides and organic triflates promoted by palladium catalyst and fluoride ion is described. Organosilicon compounds like (E) - or (Z) -alkenyl, alkynyl, allyl, and arylsilanes smoothly react with alkenyl, allyl and aryl halides to give coupled products with high chemoselectivity and stereospecificity. Under similar conditions, silylation of alkenyl iodides by hexa-methyldisilane and methylation of aryl iodides by (Et₂N)₃S⁺Me₃SiF₂^- take place. The one-pot double cross-coupling of trimethylstannyl (trimethylsilyl) acetylene with two alkenyl iodides is achieved to afford isomerically pure dienynes. The cross-coupling of chiral 1-phenyl-1-trifluorosilylethane with aryl triflates occurrs stereo-specifically, providing optically active coupled products. The stereochemistry of the products is influenced decisively by reaction temperature and solvent used. A transition state model for the transmetallation step in catalytic cycle is proposed on the basis of substituent effect and stereochemical study of this reaction.

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