Practical synthesis of Dirhodium(II) tetrakis[N-phthaloyl-(S)-tert-leucinate

An efficient and reliable procedure for the preparation of dirhodium(II) tetrakis[N-phthaloyl-(S)-tert-leucinate], Rh2(S-PTTL)(4), a universally effective catalyst for a range of enantioselective carbene transformations, is described. The N-phthaloylation of (S)-tert-leucine by the method of Bose with essentially no racemization is a key to this process.     

Catalyzed intramolecular olefin insertion into a carbon-carbon single bond

Intramolecular insertion of a C-C double bond into a C-C single bond was achieved by treatment of cyclobutanone bearing an o-styryl group at the 3-position with a catalytic amount of a cationic rhodium(I)-dppp complex. Initially, rhodium is inserted between the carbonyl carbon and the alpha-carbon of the cyclobutanone. Intramolecular coordination of the vinyl group results in its migratory insertion into the C-Rh linkage. Reductive elimination affords benzobicyclo[3.2.1]octan-3-one. Notably, a ring-opened alpha,beta-unsaturated ketone was obtained when dppe was used instead of dppp. In this reaction, rhodium cleaved the bond between the alpha sp3 carbon and the beta sp3 carbon of the cyclobutanone. The coordinating vinyl group directs this new regioselectivity of cleavage observed with the dppe ligand.     

Stereocontrolled syntheses of alpha-C-mannosyltryptophan and its analogues

The total synthesis of alpha-C-mannosyltryptophan (C-Man-Trp), a naturally occurring C-glycosylamino acid, was achieved from a commercially available alpha-methyl-D-mannoside in 10 steps including the following key steps: the C-glycosidation of a mannose derivative with a stannylacetylene, Castro indole synthesis, and Sc(ClO4)3-promoted coupling with L-serine-derived aziridine carboxylate. The glucose- and galactose-analogues of C-Man-Trp were also synthesized in a similar manner. Conformational analyses of the synthesized C-glycosyltryptophan and its synthetic intermediate are briefly discussed.     

Novel use of organotin halide-base complex in organic synthesis. Cycloaddition reaction of oxetane with isocyanates.

Cycloadditions of oxetanes with isocyanates were markedly accelerated by the complex of Bu₂SnI2 and Ph₃P=O which could be readily handled and hardly caused a trimerization of isocyanates, yielding oxazin-2-ones under neutral and mild reaction conditions.     

Ladderlike ferromagnetic spin coupling network on a pi-conjugated pendant polyradical

A poly(9,10-anthryleneethynylene)-based polyradical with two pendant stable phenoxyls in one anthracene skeleton was newly synthesized via polymerization of the corresponding bromoethynylanthracene monomer using a Pd(0) catalyst. The average molecular weight of the polymer reached M(n) = 5 x 10(3) and was soluble in common organic solvents. The polyradical was prepared from the corresponding hydroxyl precursor polymer and was appropriately stable at room temperature. The ESR spectrum of the corresponding monomeric radical suggested an effectively delocalized spin density distribution on the backbone anthracene. The magnetization and the static magnetic susceptibility of the polyradical were measured using a SQUID magnetometer. The large average spin quantum number (S = (5)/(2)) of the polyradical indicated that the ferromagnetic spin coupling network of the polyradical had spread throughout the pi-conjugated chain and that it was considerably insensitive to spin defects.     

Photochemical reactions of high polymers. XIV. Syntheses and photochemical reactions of copolymers bearing O-acyloxime groups

Copolymers bearing pendant O-acyloxime groups were synthesized by two methods: copolymerizations of oxime acrylate (methyl β-naphthyl ketone oxime acrylate or benzophenone oxime acrylate) and styrene, condensation of acrylic acid—styrene copolymer with oximes (benzophenone oxime, p-nitrobenzophenone oxime, methyl β-naphthyl ketone oxime, benzalacetone oxime or 9-fluorenone oxime). The photochemical behavior of the O-acyloxime copolymers changed markedly with the irradiation conditions: irradiation of benzene solutions led to degradation in air and crosslinking under nitrogen, while irradiation of solid films in air resulted in simultaneous degradation and crosslinking. Photolysis of methyl β-naphthyl ketone oxime acetate, a model for the O-acyloxime copolymer, in benzene solution under nitrogen resulted in scission of the N? O bond. The same reaction was observed in the irradiation of the O-acyloxime copolymers. It is suggested that formation of free radicals on the polymer chains via scission of the N? O bond is followed by decarboxylation. In the absence of oxygen, crosslinking of the polymer by recombination of the free radicals competes with degradation via β-scission. In the presence of oxygen, autoxidative degradation predominates.     

Palladium-catalyzed intermolecular three-component coupling of aryl iodides, alkynes, and alkenes to produce 1,3-butadiene derivatives

[reaction: see text] The sequential three-component coupling of aryl iodides, diarylacetylenes, and monosubstituted alkenes effectively proceeds in the presence of Pd(OAc)(2), LiCl, and NaHCO(3) as catalyst, promoter, and base, respectively, in DMF-H(2)O to produce the corresponding 1,3-butadiene derivatives.     

Absolute structures of some naturally occurring isopropenyldihydrobenzofurans,remirol, remiridiol,angenomalin, and isoangenomalin

The absolute structures of some naturally occurring chiral 2-isopropenyl-2,3-dihydrobenzofurans, (+)-remirol (1a), (+)-remiridiol (1b), (+)-angenomalin (2), and (+)-isoangenomalin (3), were studied by respective chiral synthesis. Kinetic resolutions of racemic 2-isopropenyl-2,3-dihydrobenzofurans, 2-isopropenyl-4,6-dimethoxy-2,3-dihydrobenzofuran (4), 4-hydroxy-2-isopropenyl-2,3-dihydrobenzofuran-5-carbaldehyde (8), and 2-isopropenyl-6-(MOM)oxy-2,3-dihydrobenzofuran-5-carbaldehyde (11c), by Sharpless dihydroxylation using (DHQ)(2)AQN or (DHQD)(2)AQN gave the corresponding chiral 2-isopropenyl-2,3-dihydrobenzofurans. Chiral (S)-(+)-4 (99% ee, using (DHQD)(2)AQN) was converted to natural remirol (S)-(+)-1a and then to natural remiridiol (S)-(+)-1b. (S)-(+)-8 (97% ee, using (DHQD)(2)AQN) was converted to natural angenomalin (S)-(+)-2. (R)-(-)-11c (>99% ee, using (DHQ)(2)AQN), was converted to natural isoangenomalin (R)-(+)-3. Thus, the absolute structures of natural remirol (+)-1a and remiridiol (+)-1b and angenomalin (+)-2 were determined to be S, and the structure of natural isoangenomalin (+)-3 was R.     

A helical amplification system composed of artificial nucleic acids

Herein we report an amplification system of helical excess triggered by nucleic acid hybridization for the first time. It is usually impossible to prepare achiral nanostructures composed of nucleic acids because of their intrinsic chirality. We used serinol nucleic acid (SNA) oligomers for the preparation of achiral nanowires because SNA oligomers with symmetrical sequences are achiral. Nanowire formation was confirmed by atomic force microscopy and size exclusion chromatography. When a chiral nucleic acid with a sequence complementary to SNA was added to the nanostructure, helicity was induced and a strong circular dichroism signal was observed. The SNA nanowire could amplify the helicity of chiral nucleic acids through nucleobase stacks. The SNA nanostructures have potential for use as platforms to detect chiral biomolecules under aqueous conditions because SNA can be readily functionalized and is water-soluble.

Herein we report an amplification system of helical excess triggered by nucleic acid hybridization for the first time.     

Selective extraction and recovery of cytochrome c by liquid-liquid extraction using a calix[6]arene carboxylic acid derivative

Recently, we reported that a calix[6]arene carboxylic acid derivative can selectively extract the lysine-rich protein cytochrome c by interacting with amino groups on the protein surface. In the present article, quantitative extraction and recovery of cytochrome c using this calix[6]arene carboxylic acid derivative are described. Both adjustment of the pH under acidic conditions and addition of an alcohol are necessary to strip the extracted protein from an organic solution to an aqueous solution. Separation of cytochrome c and lysozyme using the calix[6]arene was achieved under the optimal conditions. In the forward extraction stage, 93% of the cytochrome c was extracted, while lysozyme remained in the solution. In the subsequent stripping stage, the extracted cytochrome c was quantitatively recovered in an aqueous solution. Finally, separation of these proteins, which have similar molecular weights and isoelectric points, was accomplished.