The first highly substitutionally labile dipalladium (I) complexes are synthesized. The reaction of these reactive dipalladium (I) complexes with unsaturated hydrocarbons such as alkynes, 1, 3-dienes and 1, 3, 5-trienes is surveyed. Unique one-dimensional sandwich compounds made of a palladium chain and polyene ligands are prepared and structurally characterized.
Selenoaldehydes have been generally considered to be highly reactive species as a dienophile for cycloaddition reactions because of long bond length and poor overlap in the carbon-selenium π bond, so they are one of the important intermediates in the synthesis of selenium-containing heterocycles. Selenoaldehydes, directly generated by the reaction of aromatic and aliphatic aldehydes with bis (dimethylaluminum) selenide as a selenating reagent, were in situ effectively trapped by anthracene to give [4 + 2] cycloadducts (1) in good yields as a stable solid in the most cases. 1 decomposed quantitatively via thermal retro Diels-Alder reaction to regenerate the corresponding selenoaldehydes under neutral conditions. Thus 1 can serve as convenient and clean precursors of selenoaldehydes. Cycloadducts 1 were heated with 2-trimethylsilyloxy-1, 3-butadiene in toluene at reflux temperature, followed by addition of trifluoroacetic acid to afford a mixture of 3-and 4-selenacyclohexanones in good yields. The regiochemistry in this cycloaddition reaction was influenced by electronic character of a substituent on selenoaldehydes. Thermally generated selenoaldehydes from 1 reacted with 2-methoxyfuran to give 5-substituted penta-2, 4-dienoates as a mixture of four geometrical isomers in excellent yields along with the deposition of elemental selenium. On the other hand, the reaction of selenoaldehydes with 5-alkoxyoxazoles afforded 1 : 1 adducts having 3-selenazoline structure as a mixture of diastereomers in good yields, regioselectively. Furthermore, aromatic selenoaldehydes reacted with nitrile oxides or nitrile imines under neutral conditions to afford the [3 + 2] cycloadducts with a complete regioselectivity in excellent yields.
Preparation and properties of organic radicals directed toward spin systems with multi-property are described, in which aminoxyl (nitroxide) radicals are incorporated as the crucial building blocks. Those include such organic radicals that exhibit the magnetic properties responding to or correlating with outer stimuli as heat (liquid crystalline property), light (photo-functionality), electron/hole (conducting property), or pressure (pressure-responsive property).
Synthetic studies of imidazole C-nucleoside derivatives and their application to novel histamine H3- and H4-ligands are described, in which the following items are covered. 1) Stereoselective synthesis of imidazole C-nucleosides via diazafulvene intermediates. 2) Synthesis of tetrahydrofuranylimidazoles using efficient use of a PhSe group and its application to novel histamine H3-ligands. 3) Histamine H3- and H4-agonistic activities of imifuramine derivatives. 4) Efficient synthesis of imifuramine and its stereoisomer via diazafulvene intermediates. 5) Difference between diazafulvene cyclization and intramolecular Mitsunobu reaction of 1, 4-diols.
Using highly cross-linked polystyrene-supported chiral phosphine-phosphite (R, S) -BINAPHOS-Rh (I) complexes, olefins were hydroformylated to give the corresponding iso-aldehydes in high ee's in benzene suspension. The efficiency in catalytic activity and selectivity is at the highest level among the heterogeneous catalysis recorded to date. In a batch equipped with a fixed bed of a polystyrene-supported (R, S) -BINAPHOS-Rh (I), gaseous substrates, cis-2-butene and 3, 3, 3-trifluoropropene, were smoothly converted into the corresponding iso-aldehydes with high selectivities (100 % regioselectivity and 80 % ee for cis-2-butene, 93 % regioselectivity and 90 % ee for 3, 3, 3-trifluoropropene) under vapor-phase reaction conditions. When the asymmetric hydroformylation of 3, 3, 3-trifluoropropene was carried out in a continuous vapor-flow column reactor, 2-trifluoromethylpropanal was obtained with 95 % regioselectivity and 90 % ee. Such less volatile olefins as styrene, vinyl acetate, 1-alkenes, polyfluorinated alkenes, were also converted into the corresponding aldehydes with high selectivities comparable to those obtained under homogeneous conditions, when they were injected through scCO2-flow column reactor in a stepwise manner. Substituents were incorporated at the phenyl groups of (R, S) -BINAPHOS. Using Rh catalysts complexed by 3-methoxy substituted ligand, olefins were hydroformylated to give iso-aldehydes, whose regio- and enantioselectivities were improved as compared with the unsubstituted ligand. Asymmetric hydroformylation of styrene with Rh (I) - (un) substituted ligands was monitored by in situ high pressure IR to disclose the aldehyde-production rate was robs = kobs [Rh] 1.0 [styrene] 0.6 [ligand] -0.1PCO-0.9 (kobs : a constant under isothermal conditions). Higher catalytic activity observed with 3-methoxy substituted ligand compared to that with normal ones is attributed to higher concentration of an active species. An alkoxy-substituted ligand was incorporated into polystyrene, and the resulting polymer-supported (R, S) -BINAPHOS-Rh (I) complex was successfully used for asymmetric hydroformylation of various olefins.
We have exploited the novel strategies for construction of N-heterocycles using Chloramine-T as an N 1 unit. Copper (I) chloride or iodine was found to be a good catalyst for aziridination of various alkenes with Chloramine-T. The combination of Chloramine-T and silver nitrate directly led to not only aziridines from alkenes including α, β-unsaturated carbonyl compounds but also bicyclic pyrrolidines from 1, 6-dienes. The synthesis of pyrrolidine derivatives was achieved efficiently and stereoselectively from alkenyl iodides and Chloramine-T, in which the iodo group of the substrates has multiple functions to perform the cyclization. Furthermore, organic-solvent-free aziridination of alkenes was developed by utilizing Chloramine-T-I2 system under phase-transfer catalyst conditions or under the reaction media of silica and water.
In recent years, much attention has been focused on the catalytic activity of iridium complexes bearing a pentamethylcyclopentadienyl (Cp*) as a supporting ligand. We and other several groups have revealed the catalytic activity of Cp* iridium complexes toward hydrogen transfer reactions. In this article, these new catalytic hydrogen transfer reactions are surveyed.