Highly chemo-, regio- and/or stereoselective addition of organic dichalcogenides to carbon-carbon unsaturated bonds has been achieved based on two different methodologies for activation of the chalcogen-chalcogen bonds, i.e., by the aid of transition metal catalysts and by photoirradiation. The former is the novel transition metal-catalyzed reactions of organic dichalcogenides with acetylenes via oxidative addition of dichalcogenides to low valent transition metal complexes such as Pd (PPh3) 4. The latter is the photoinitiated radical addition of organic dichalcogenides to carbon-carbon unsaturated bonds via homolytic cleavage of the chalcogen-chalcogen bonds to generate the corresponding chalcogen-centered radicals as the key species.
A series of functionalized porphyrins were prepared to show their potential for the models of various types of receptors. Atropisomerization was controlled by the combination of meso substituents and β-substituents. Chiral porphyrins were also prepared according to several different approaches. Molecular recognition functions of these functional porphyrins are also described. Perfluoroalkylporphyrins showed characteristic oxidation potential and can serve as a 19F NMR probe. They are applied to anovel catalyst and to the study of heme-protein interactions.
The lithium salt of trimethylsilyldiazomethane (TMSC (Li) N2) smoothly reacts with alkyl aryl ketones and aldehydes to give the corresponding homologous alkynes via alkylidene carbene intermediates. In the case of aliphatic ketones, the resulting alkylidene carbenes can be trapped by an amine to afford enamines which are efficiently converted to the homologous aldehydes. TMSC (Li) N2 can also be effectively used for the preparation of heterocycles such as 2, 3-dihydrofurans, cyclohepta [b] pyrrol-2-ones, and 3-pyrrolines from the corresponding β-siloxyketones, N-methylanilides of α-keto acids, N, N-dialkylamides of α-keto acids, and N, N-disubstituted α-amino ketones, respectively.
By utilizing the characteristic features of vinylsulfides, 2- (alkylthio) allyl silyl ethers were designed as efficient ene substrates, and their use led to exploration of general carbonyl and imine ene reactions. By using 3- (alkylthio) -2-siloxyallyl acetates, a useful [3 + 2] cyclopentane annulation methodology was developed. Further, a tandem C-C bond formation/cleavage methodology was also designed.
Intra- and inter-molecular Michael addition of allenecarboxylates, derived from penicillins, may offer straightforward synthetic routes to 2-exo-methylenepenams and C (3) - substituted Δ3-cephems. Thus obtained 2-exo-methylenepenams are divergent intermediates for penem and penam families of antibiotics or potent β-lactamase inhibitors. The intermolecular Michael addition of the allenecarboxylates can achieve construction of the cephem framework as well as introduction of various C (3) -substituents, e.g., amino, sulfenyl, chloro, and alkenyl groups. In place of the allenecarboxylates, 3, 4-disubstituted 2- [4- (phenylsulfonylthio) -2-oxoazetidin- 1 -yl] -2-butenoates work as a promising precursor of both the 2-exo-methylenepenams and 3-chloro-Δ3-cephems.
This article discloses self-assembling finite and infinite coordination compounds with unique structures and properties. Macrocycles, catenanes, and cages selfassemble quantitatively from a cis protected Pd (H) complex and appropriate pyridine-based bridging ligands. These discrete structures are expanded to infinite frameworks when the same ligands are complexed with a non-protected Cd (II) ion.
By oxidation of β-keto acids, cyclopropanols, and acyl chromate complexes with tris (2-pyridinecarboxylato) manganese (III) (Mn (pic) 3), α-keto, β-keto, and alkyl radicals are generated respectively, which react with olefinic compounds to afford intermolecular addition products in good yield. On the other hand, the cation radicals can be generated from α-stannylalkyl sulfides, α-stannylalkyl amine derivatives, and α-stannyl carboxylic esters by oxidation with ammonium hexanitratocerate (N) (CAN). These cation radicals of stannyl compounds readily cleave into carbocation or radical species, which are utilized as reactive intermediates for carbon-carbon bond formation.
Recent synthetic work on typical cell surface glycoconjugates of bacteria which activate the immunological system of higher animals is described. Lipid A, previously proved to be the active entity of lipopolysaccharide of Gram-negative bacteria, was subjected to further study and novel efficient routes were established for its structural analogs and a 3H-labeled derivative. Proposed structures of lipoteichoic acids from Gram-positive bacteria were also synthesized to lead to the conclusion that not the major components corresponding to the proposed structures but other minor ones are responsible for the activity.
The full potential of rhodium (II) -catalyzed intramolecular C-H insertion reactions of α-diazo carbonyl compounds as a powerful tool for the construction of both carbocycles and heterocycles has been developed by variation of the bridging ligands of the dirhodium (II) catalysts : (1) Dirhodium (II) tetrakis (triphenylacetate) featured by the steric bulk of the bridging ligands on the rhodium has been demonstrated to exhibit an exceptionally high order of selectivity for C-H insertion into methylene over methine on a cycloalkane ring as well as for aromatic substitution over aliphatic C-H insertion. (2) Dirhodium (II) complexes incorporating N-phthaloyl- (S) -amino acids as bridging ligands have proven to be the chiral catalysts of choice for allowing high levels of differentiation of enantiotopic methylene C-H bonds and enantiotopic benzene rings, affording optically active cyclopentanone, 2-azetidinone, and 2-indanone derivatives in up to 80%, 96%, and 98% ee, respectively.
The stereochemical features and synthetic potentials are described of the classic [1, 2] -Wittig rearrangement which is now recognized to proceed via the radical cleavagerecombination mechanism. First, the [1, 2] -Wittig rearrangement of enantio-defined α-benzyloxypropyllithium and its (R) -α-methylbenzyloxy analogs is shown to proceed predominantly with inversion of configuration at the Li-bearing terminus and retention of configuration at the migrating carbon. Second, the [1, 2] -Wittig rearrangement of O-glycosides of both acetal and ketal types, including those derived from D-ribose and D-glucose, is demonstrated to proceed with complete retention of either the α- or β-anomeric configuration, along with efficient stereocontrol over the newly created chiral center on the side chain to afford the novel classes of stereo-defined C-glycosides in good yields.