Photocycloaddition reaction of methyl 2- and 3-chromonecarboxylates with various alkenes

The irradiation of methyl 2- and 3-chromonecarboxylate in the presence of various alkenes afforded cyclobutane type adducts, whose structures were established by X-ray structural analysis. Methyl 2-chromonecarboxylate showed higher photochemical reactivity than methyl 3-chromonecarboxylate, in which endo adducts were yielded as major products.     

Diastereo‐ and Regioselective Addition of Thioamide Dianions to Imines and Aziridines: Synthesis of N‐Thioacyl‐1,2‐diamines and N‐Thioacyl‐1,3‐diamines

Addition reactions of thioamide dianions that were derived from N‐arylmethyl thioamides to imines and aziridines were carried out. The reactions of imines gave the addition products of N‐thioacyl‐1,2‐diamines in a highly diastereoselective manner in good‐to‐excellent yields. The diastereomeric purity of these N‐thioacyl‐1,2‐diamines could be enriched by simple recrystallization. The reduction of N‐thioacyl‐1,2‐diamines with LiAlH₄ gave their corresponding 1,2‐diamines in moderate‐to‐good yields with retention of their stereochemistry. The oxidative‐desulfurization/cyclization of an N‐thioacyl‐1,2‐diamine in CuCl₂/O₂ and I₂/pyridine systems gave the cyclized product in moderate yield and the trans isomer was obtained as the sole product. On the other hand, a similar cyclization reaction with antiformin (aq. NaClO) as an oxidant gave the cis isomer as the major product. The reactions of N‐tosylaziridines gave the addition products of N‐thioacyl‐1,3‐diamines with low diastereoselectivity but high regioselectivity and in good‐to‐excellent yields. The use of AlMe₃ as an additive improved the efficiency and regioselectivity of the reaction. The stereochemistry of the obtained products was determined by X‐ray diffraction.     

Copper‐Catalyzed CH Bond Direct Chalcogenation of Aromatic Compounds Leading to Diaryl Sulfides,Selenides, and Diselenides by Using Elemental Sulfur and Selenium as Chalcogen Sources Under Oxidative Conditions

The reactions of aromatic compounds and elemental chalcogens catalyzed by a copper salt with molecular oxygen as an oxidant were carried out. The reaction of 3‐substituted imidazo[1,5‐a]pyridines and elemental sulfur in the presence of CuTC (copper(I) thiophenecarboxylate) gave the corresponding bisimidazopyridyl sulfides in good to quantitative yields. The reaction proceeded even under aerobic oxidation conditions. The use of a polar solvent was crucial for the reaction, and DMSO (dimethyl sulfoxide) in particular stimulated the reaction. The reaction could be applied to common aromatic compounds, such as N‐methyl indole and dialkyl anilines. The reaction of indole proceeded at the nucleophilic C3 position rather than at the acidic C2 position. In addition, the reaction of dialkyl anilines proceeded with an ortho, para orientation. The reactions of imidazopyridines and elemental selenium under similar conditions gave the corresponding bisimidazopyridyl diselenides along with bisimidazopyridyl monoselenides. The resulting diselenides were readily converted to the corresponding monoselenides with unreacted imidazopyridines under the same conditions. The reaction could be applied to the copolymerization of bifunctional bisimidazopyridines and elemental sulfur to give oligomeric copolymers in quantitative yield.     

Grubbs carbene complex-catalyzed cleavage of allyl vic-diols to aldehydes with a co-oxidant: application to the selective cleavage of huge marine molecules

An oxidative cleavage of allyl vic-diols to aldehydes catalyzed by a Grubbs carbene complex using a co-oxidant has been established for the first time, with good yields. The utility of this selective cleavage reaction was demonstrated through the use of two huge marine molecules, symbiodinolide and N-p-BrBz palytoxin.     

Palladium(II)-catalyzed sequential hydroxylation-carboxylation of biphenyl using formic acid as a carbonyl source

[reaction: see text] A simultaneous hydroxylation-carboxylation of biphenyl occurred to give 4'-hydroxy-4-biphenylcarboxylic acid, which has wide potential application as a polyester monomer.     

A new ketone synthesis by palladium-catalyzed cross-coupling reactions of esters with organoboron compounds

[reaction: see text] The palladium-catalyzed coupling reaction of 2-pyridyl esters with organoboron compounds is described. The reaction is compatible with various functional groups and proceeds under mild reaction conditions. The coordination of the nitrogen atom to Pd is a key step for efficient reaction.     

Mammalian-specific genomic functions: Newly acquired traits generated by genomic imprinting and LTR retrotransposon-derived genes in mammals

Mammals, including human beings, have evolved a unique viviparous reproductive system and a highly developed central nervous system. How did these unique characteristics emerge in mammalian evolution, and what kinds of changes did occur in the mammalian genomes as evolution proceeded? A key conceptual term in approaching these issues is “mammalian-specific genomic functions”, a concept covering both mammalian-specific epigenetics and genetics. Genomic imprinting and LTR retrotransposon-derived genes are reviewed as the representative, mammalian-specific genomic functions that are essential not only for the current mammalian developmental system, but also mammalian evolution itself. First, the essential roles of genomic imprinting in mammalian development, especially related to viviparous reproduction via placental function, as well as the emergence of genomic imprinting in mammalian evolution, are discussed. Second, we introduce the novel concept of “mammalian-specific traits generated by mammalian-specific genes from LTR retrotransposons”, based on the finding that LTR retrotransposons served as a critical driving force in the mammalian evolution via generating mammalian-specific genes.     

Structural properties of charge-transfer complexes of multilayered [3.3]paracyclophanes

In the solid state, multilayered [3.3]paracyclophanes (PCPs) 2-6 and tetracyanoethylene (TCNE) form charge-transfer (CT) complexes with a 1:1 stoichiometry. All the benzene rings overlapped each other. All the [3.3]PCP units and dione units assume chair conformations and the transannular distances are shorter than those of the corresponding free multilayered [3.3]PCP except for the dione unit in the four-layered dione 6. In the crystal-packing diagrams, the PCP and TCNE are located in alternating donor-acceptor stacking in columns, and effective short contacts are observed in the neighboring molecules.