Diacetoxylation of conjugated dienes with thallium(III) acetate in acetic acid

The reaction of conjugated dienes such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2,5-dimethyl-2,4-hexadiene, 1,3-cyclopentadiene, and 1,3-cyclohexadiene, with thallium(III)acetate in acetic acid at 10–65° for 0.5–15 hr affords an isomeric mixture of the corresponding diacetoxyalkenes (1,2- and 1,4-addition products) in 10–92% yields. The 1,2-addition products are predominantly formed in all cases examined except the case of 1,3-cyclopentadiene. The reaction is assumed to proceed through acetoxythallation and dethallation steps, the latter step being accompanied and/or followed by an attack of acetoxyl group. An initial attack of thallium moiety is proposed to occur mainly at C-1 and C-2 carbons in the cases of linear terminal dienes and cyclic dienes, respectively.     

Ruthenium-catalyzed propargylic substitution reactions of propargylic alcohols with oxygen-, nitrogen-, and phosphorus-centered nucleophiles

The scope and limitations of the ruthenium-catalyzed propargylic substitution reaction of propargylic alcohols with heteroatom-centered nucleophiles are presented. Oxygen-, nitrogen-, and phosphorus-centered nucleophiles such as alcohols, amines, amides, and phosphine oxide are available for this catalytic reaction. Only the thiolate-bridged diruthenium complexes can work as catalysts for this reaction. Results of some stoichiometric and catalytic reactions indicate that the catalytic propargylic substitution reaction proceeds via an allenylidene complex formed in situ, whereby the attack of nucleophiles to the allenylidene C(gamma) atom is a key step. Investigation of the relative rate constants for the reaction of propargylic alcohols with several para-substituted anilines reveals that the attack of anilines on the allenylidene C(gamma) atom is not involved in the rate-determining step and rather the acidity of conjugated anilines of an alkynyl complex, which is formed after the attack of aniline on the C(gamma) atom, is considered to be the most important factor to determine the rate of this catalytic reaction. The key point to promote this catalytic reaction by using the thiolate-bridged diruthenium complexes is considered to be the ease of the ligand exchange step between a vinylidene ligand on the diruthenium complexes and another propargylic alcohol in the catalytic cycle. The reason why only the thiolate-bridged diruthenium complexes promote the ligand exchange step more easily with respect to other monoruthenium complexes in this catalytic reaction should be that one Ru moiety, which is not involved in the allenylidene formation, works as an electron pool or a mobile ligand to another Ru site. The catalytic procedure presented here provides a versatile, direct, and one-step method for propargylic substitution of propargylic alcohols in contrast to the so far well-known stoichiometric and stepwise Nicholas reaction.     

Ruthenium-catalyzed propargylic substitution reaction of propargylic alcohols with thiols: a general synthetic route to propargylic sulfides

A novel cationic methanethiolate-bridged diruthenium complex [Cp*RuCl(mu2-SMe)2RuCp*(OH2)]OTf (1e) has been disclosed to promote the catalytic propargylic substitution reaction of propargylic alcohols bearing not only terminal alkyne group but also internal alkyne group with thiols. It is noteworthy that neutral thiolate-bridged diruthenium complexes (1a-1c), which were known to promote the propargylic substitution reactions of propargylic alcohols bearing a terminal alkyne group with various heteroatom- and carbon-centered nucleophiles, did not work at all. The catalytic reaction described here provides a general and environmentally friendly preparative method for propargylic sulfides, which are quite useful intermediates in organic synthesis, directly from the corresponding propargylic alcohols and thiols.     

New cyclic tellurides. Synthesis, reaction and ligand properties of 2,2,6,6-tetramethyl-1-oxa-4-tellura-2,6-disilacyclohexane (C6H16OSi2Te). X-Ray structure determination of C6H16OSi2TeI2

A new tellurium-containing heterocyclic compound, 2,2,6,6-tetramethyl-1-oxa-4-tellura-2,6-disilacyclohexane (C₆H₁₆OSi₂Te) (1), has been prepared by treatment of 1,3-bis(chloromethyl)-1,1,3,3-tetramethyldisiloxane with sodium telluride. Mononuclear and dinuclear palladium complexes of this telluride have been prepared by the reaction of 1 with PdCl₂(PhCN)₂ and Na₂PdCl₄, respectively. The following new derivatives of 1 have also been produced: C₆H₁₆OSi₂TeI₂ (2), C₆H₁₆OSi₂TeBr₂, C₆H₁₆OSi₂TeCl₂, C₆H₁₆OSi₂Te(CH₃)I, and C₆H₁₆OSi₂Te(CH₂Ph)Br. IR, ¹H and ¹³C NMR and mass spectral data of these new compounds are reported and discussed. ¹H NMR studies revealed that in CDCl₃ solution both telluronium salts reductively eliminate alkyl halide. The crystal structure of compound 2 has been determined by X-ray diffraction. The compound crystallizes in the monoclinic space group, P2₁/c, with four molecules in a unit cell of dimension a 12.960(3), b 8.846(2), c 13.754(4) Å, β 92.44(2)°, R = 0.049, and R_w = 0.067 for 3599 unique reflections with |F₀| > 3σ(F₀). The compound forms a six-membered ring of a slightly displaced boat type. The geometry about the Te atom is pseudo-octahedral, with two carbon atoms (Te-C = 2.156(7) and 2.137(6) Å) and two iodine atoms of the neighbouring molecules (weak intermolecular bonds, Te · I = 3.769 and 3.806 Å) in the equatorial positions and two iodine atoms (Te-I = 2.909(1) and 2.913(1) Å) in the axial positions.     

Highly Selective Asymmetric Intramolecular Selenocyclisation

Asymmetric intramolecular selenocyclisation of alkenoic acids, alkenols and alkenyl urethanes using chiral ferrocenylselenenyl cations proceeds smoothly to give the corresponding lactones, cyclic ethers and N-heterocyclic compounds, respectively, in moderate yields with very high diastereoselectivities.     

Chiral Bis(oxazoline)-copper Catalyzed Enantioselective Imidation of Sulfides

Prochiral sulfides reacted with Phl=NTs in the presence of a catalytic amount of Cu(I) salt together with a chiral 4,4′-disubstituted bis(oxazoline) ligand to afford the corresponding chiral sulfimides.     

Retrospect of Se and Te Chemistry

Retrospect of organoselenium and tellurium chemistry for these 30 years is described focusing on our novel findings in this field: (1) telluroxide elimination leading to alkenes and allylic compounds, (2) Pd-catalyzed or –mediated carbodetelluration for a new C–C bond formation, (3) synthesis of chiral diferrocenyl dichalcogenides and their use as chiral auxiliaries, (4) asymmetric selenoxide elimination for making optically active allenes and alkenes, (5) meta chloroperbenzoic acid (MCPBA) oxidation of organic selenides and tellurides leading to a substitution of a PhSe or PhTe moiety, as well as (6) preparation of chalcogen-bridged diruthenium complexes and their catalytic use for propargylic substitution reactions.     

Beam-size measurement with optical diffraction radiation at KEK accelerator test facility

An experiment on the investigation of optical diffraction radiation (ODR) from a slit target as a possible tool for noninvasive electron beam-size diagnostics has been performed at the KEK accelerator test facility. The experimental setup has been installed at the diagnostics section of the extraction line. We have performed the first incoherent ODR observation from a slit target. The measured angular distributions are in reasonable agreement with the theoretical expectation. The beam-size effect onto the ODR angular pattern has been observed. Moreover, the sensitivity to the beam size as small as 14 microm has been achieved.