Synthesis, structure, and reactions of novel acyclic and cyclic disilenes are discussed in detail. Due to the distinctive electronic and steric effects of trialkylsilyl substituents, tetrakis (trialkylsilyl) disilenes show interesting structural features around Si=Si bonds, electronic spectra, and reactions. Photochemical and thermal interconversion among Si4R6 isomers including a cyclotetrasilene, a silylcyclotrisilene, and a bicyclo [1.1.0] tetrasilane occurs without apparent participation of the corresponding tetrasila-1, 3-diene. In contrast to parent spiropentadiene, which is the simplest spiro-conjugation system but has been missing as an isolable molecule in carbon chemistry, a synthesized spiropentasiladiene is thermally very stable and shows remarkable spiroconjugation between the two ring π systems. In contrast to carbon allenes, the skeleton of a trisilaallene, the first stable silicon compound with formally sp-hybridized silicon atom, is significantly bent and remarkably fluxional. Tetrasilyldisilenes are useful reagents for the synthesis of novel types of organosilicon compounds such as η2-disilene transition metal complexes and a 1, 3-disilabicyclo [1.1.0] butane.
Octasilacubane is an intriguing polyhedral polysilane because of its unique electronic properties arising from highly strained Si-Si σ-bonded framework. The first octasilacubane, octakis (t-butyldimethylsilyl) octasilacubane was reported by our group in 1988, as the first example of Platonic solid compounds comprising Group 14 elements other than carbon. We then prepared the alkyl-substituted one (ThexSi)8 (Thex = 1, 1, 2-trimethylpropyl) in 1992. These octasilacubanes are fairly stable, and various reactions, e.g., halogenation, oxidation, and photoreaction have been reported. Thus, the reaction of (ThexSi)8 with PCl5 leading to dichlorides via skeletal, rearrangement, the halogenation with Br2 or I2 leading to dibromides or diiodides, and the reductive dehalogenation of these dihalides with sodium to regenerate (ThexSi)8. Photo-initiated partial oxidation with DMSO gave monooxaoctasilahomocubane and dioxaoctasilabishomocubane. In this paper, in addition to these reactions, structure, thermal property, photoluminescent property, and UV property of octasilacubanes were summarized.
Various aqueous oxidation reactions have been developed since economic and environmental concerns encourage the use of water as a reaction medium. Hypervalent iodine compounds have been used extensively in organic synthesis due to not only low toxicity, ready availability, and easy handling, but also reactivities similar to those of heavy metal reagents or anodic oxidation. However, most of the hypervalent iodine oxidation reactions have been carried out only in limited organic solvents because both the solubility and the reactivity of organo-iodine (III or V) compounds have remarkably been decreased in water. In this article, we report novel activation methods of hypervalent iodine species in water and their application to the development of environmentally benign oxidation reactions using polymer-supported iodine (III) reagents. Furthermore, these methods enabled us to replace iodine (V) reagents, such as Dess-Martin periodinane (DMP) and ο-iodoxybenzoic acid (IBX) with much safer (non-explosive) and commercially available iodine (III) reagents.
tert-Butanesulfinyl imines are exceedingly versatile intermediates for the asymmetric synthesis of amines. Aldimines 15 and ketimines 16 are prepared in high yields under mild conditions by condensing enantiomerically pure tert-butanesulfinamide 10, either enantiomer of which is readily synthesized in large scale from inexpensive reagents, with a wide range of aldehydes and ketones. The tert-butanesulfinyl group activates the imines for the addition of many different classes of nucleophiles, serves as a powerful chiral directing group, and after nucleophilic addition function as a versatile protecting group of the amines, which is readily cleaved by treatment with acid. A wide range of highly enantioenriched amines, including α-branched amines, α, α-dibranched amines, α- and β-amino acids, 1, 2- and 1, 3-amino alcohols, and α-trifluoromethylamines are efficiently synthesized using this methodology.
Stable 4, 7-disubstituted benzotrichalcogenoles containing sulfur, selenium, and tellurium atoms in the five-membered ring were systematically and selectively prepared in good yields by reaction, of the corresponding benzodichalcogenastannoles or benzodichalcogenatitanoles, synthetic equivalents of benzenedichalcogenols, with an S1 or Se1 source. Characterization of these new trichalcogenole frameworks was performed by multi-nuclear 119Sn, 77Se, 125Te NMR studies and X-ray crystallographic analyses. The cyclic voltammograms of the trichalcogenoles showed well-defined reversible electrochemical redox couples with low oxidation potential. Novel radical ions were isolated in quantitative yields in the one-electron oxidation of the trichalcogenoles with 1 equiv. of NOPF6 as a one-electron oxidant. The structures of the radical cation salts were analyzed by 31P NMR and ESR spectroscopies, and elemental analyses. The salts underwent one-electron reduction on treatment with 1 equiv. of samarium (II) iodide to give the neutral starting trichalcogenoles quantitatively.
The recent development of selenium-containing tetrathiafulvalene (TTF) -type electron donors is described, in terms of the synthetic chemistry and thus developed new electron donors and (super) conductors. Introduction of two breakthrough reactions, the one-pot preparation of 1, 3-dichalcogenole-2-chalcogenones from terminal alkynes and the formation of heterocyclic rings via transalkylation on a chalcogen atom, has made it possible, in combination with conventional trialkyl phosphite-promoted coupling reaction, to synthesize various selenium-containing TTF-type electron donors. In particular, the synthetic method is very useful for the synthesis of various tetraselenafulvalene (TSF) derivatives so far inaccessible. Such new electron donors include methylenedithiotetraselenafulvalene (MDT-TSF) and methylenedithiodiselenadithiafulvalene (MDT-ST), both of which produce a series of unique organic superconductors with Tc = 3.2-5.5 K.