N-fusion reaction sequence of heptaphyrin(1.1.1.1.1.1.1): singly, doubly, and quadruply N-fused heptaphyrins

meso-Heptakis(pentafluorophenyl) heptaphyrin(1.1.1.1.1.1.1) (1) was prepared by a stepwise route in 39 % yield and its unique N-fusion reaction (NFR) sequence has been revealed; this reaction leads to singly-, doubly-, and quadruply N-fused heptaphyrins (4, 5, and 6) in good yields. These transformations are facilitated by the inherent conformational distortion of 1 as well as the distorted, folded conformations of N-fused heptaphyrins 4 and 5. The proximate arrangement of the three pyrrole units in 6 allowed for the formation of the tripyrrolylboron(III) complexes 7, 8, and 9 with unique coordination features. Molecules 1, 5, and 9 were structurally characterized by X-ray crystallography. In addition, the boron complexes 7, 8, and 9 displayed weak but distinct fluorescence in the near infrared region.     

Pentacoordinate 1H-phosphirenes: reactivity, bonding properties, and substituent effects on their structures and thermal stability

The synthesis, reactivity, and bonding properties of several pentacoordinate P-phenyl-substituted 1H-phosphirenes are discussed. X-ray crystallographic analysis of one of them reveals a highly distorted square pyramidal (SP) arrangement around the phosphorus. NMR studies confirm that they retain the SP structure in solution and demonstrate that the endocyclic P-C bonds in the three-membered ring have a very high degree of p character, which results from their being both basal bonds in the SP structure and endocyclic bonds of the three-membered ring. Structural parameters of the three-membered ring of the pentacoordinate phosphirenes obtained by experiment and theoretical calculations are very close to those of a tetracoordinate phosphirenium cation. Thus, by analogy with tetracoordinate phosphirenium cations, it can be considered that a sigma-pi interaction between the sigma orbital of the apical bond and the pi orbital of the C=C bond in the three-membered ring is operative in pentacoordinate phosphirenes. The sigma-pi interaction is found to lower the reactivity of the C=C bond of the three-membered ring. The reactivities of the pentacoordinate phosphirenes are also affected by the substituent on the carbon atom in the three-membered ring.     

Iron-catalyzed cross-coupling of alkenyl sulfides with Grignard reagents

[reaction: see text] The iron-catalyzed cross-coupling reaction of alkenyl sulfides with Grignard reagents is described. While the cross-coupling proceeds efficiently at alkenyl-S bonds, almost no cross-coupling takes place at aryl-S bonds, attesting to a unique selectivity of iron catalysis. The beneficial effect of potentially coordinating 2-pyrimidyl group on sulfur is also described.     

Powder-to-powder polycondensation of natural saccharides. Facile preparation of highly branched polysaccharides

Solid-state polycondensation of a natural saccharide was found to take place in the presence of H3PO4(5 mol%) at 110 degrees C under a N2 flow, giving a highly branched polysaccharide (conv. 11-84%, Mw = 1400-19000, Mn = 1200-3700); the reaction mixture was powdery throughout the polymerization. Interestingly, alpha- and beta-anomers showed different polymerization behaviour; the former was polymerized more slowly, however, they gave comparable molecular weight polymers. The polysaccharide product was per-O-methylated and subjected to structure analyses. The acid-hydrolysis products, the partially O-methylated monosaccharides, suggested that the polysaccharide products have highly branched structures. MALDI-TOF mass analysis revealed that intramolecular glycosylation and acetal exchange reactions are involved in the polymerization mechanism.     

Preparation of Weinreb amides using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM)

Weinreb amides were successfully prepared from the corresponding carboxylic acids using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) in the solvents, methanol, isopropyl alcohol, and acetonitrile, which can solubilize DMT-MM. A variety of carboxylic acids were converted to the corresponding Weinreb amides in excellent yields by simply mixing with DMT-MM and N,O-dimethylhydroxylamine hydrochloride.     

Evidence of Transannular Bonding Interaction between Two Sulfur Atoms on Photolysis of Naphtho[1,8-ef][1,4]dithiepins

Naphtho[1,8-ef][1,4]dithiepins 5 were prepared by the reaction of naphtho[1,8-de]-1,3-dithiins 3 with diethyl diazomalonate in the presence of copper acetylacetonate. The X-ray crystallographic analysis of 2,3-dihydro-2,2-bis(ethoxycarbonyl)-3-phenylnaphtho[1,8-ef][1,4]dithiepin (5a) revealed that the S.S distance is shorter than the sum of their van der Waals radii, indicating that compounds 5 have a strong through-space interaction between the two sulfur atoms. Direct irradiation of 5 with a 500 W high-pressure mercury lamp (313 nm) at room temperature gave the corresponding olefins 6 and naphtho[1,8-cd]-1,2-dithiole (1) quantitatively. The quantum yields of the consumption of 5a and the formation of 6aand 1 were 0.34. The mechanism of this reaction was investigated by examining the effect of sensitization and light intensity. The results indicate that the reaction may proceed by a one-photon process from an excited singlet state. Ab initio calculations were carried out on model compound 7, and it was shown that the excitation to the S(1) state causes a bonding interaction between the two sulfur atoms, making the reaction possible.     

Amino acids and peptides. LV. Application of 2-adamantyl derivatives as protecting groups to the synthesis of peptide fragments related to Sulfolobus solifataricus ribonuclease. II.

Segment condensations were performed to construct peptide fragments related to Sulfolobus solifataricus Ribonuclease. At each condensation step, the new protecting groups were stable. The protected peptide fragments were treated with a low-high HF procedure to give the desired peptide fragments. These peptide fragments were also prepared by the solid-phase method, and the obtained peptides were compared with those obtained by the solution method. The peptide fragments obtained by the solution method were identical with those obtained by the solid-phase method on analytical HPLC, indicating that the new protecting groups could be easily removed by HF, and no racemization occurred during the synthesis of the protected peptides.