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Ion Ghiviriga

Publications and source records attributed to Ion Ghiviriga.

27 records · Page 2Linked to original sources
PubMed2003

4,5-dehydro- and 4,5,15,16-bis(dehydro)octafluoro[2.2]paracyclophanes: facile generation and extraordinary Diels-Alder reactivity.

Dehydroiodination of 4-iodo- and 4,15-diiodo-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane by treatment with KO(t)Bu in the presence of benzene, naphthalene, anthracene, and [2.2]paracyclophane affords each of the corresponding Diels-Alder mono- and bis-cycloadducts derived from the presumed aryne intermediates in high yield. Monoadducts of t-butylbenzene and furan are also obtained in excellent yield. All of the products were characterized by their NMR spectra, with four of them also being confirmed by X-ray crystallography. The extraordinary selectivity/reactivity of the aryne intermediate is discussed.

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PubMed2002

Steric hindrance to the solvation of melamines and consequences for non-covalent synthesis.

Steric hindrance to solvation disfavors structures like 1 synanti in which the melamine exposes to the solvent faces, such as tBu-H, for whom binding to the ring nitrogen is hindered but not blocked; steric hindrance to solvation lowers the barriers to rotation in solvents which bind the triazine nitrogens, therefore these solvents display the fastest rates for assembling/disassembling processes.

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PubMed2002

Two-step electrochemical annulation for the assembly of polycyclic systems.

[reaction: see text] A two-step electrochemical annulation has been developed for the preparation of fused furans. The process involves an initial conjugate addition of a furyethyl cuprate and trapping of the enolate as the corresponding silyl enolether. The second step of the annulation involves the anodic coupling of the furan and the silyl enol ether to form a six-membered ring.

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PubMed2002

Synthesis, structure, and biological evaluation of novel N- and O-linked diinositols.

Several O-and N-linked inositols and/or aminoinositols have been prepared by iterative opening of epoxides and aziridines derived from homochiral cyclohexadiene cis-diols. The three inositols and their intermediate conduritols (conduramines) were tested against several glycosidases (alpha- and beta-glucosidase, alpha- and beta-galactosidase, alpha- and beta-mannosidase) in an assay that measured the rate of hydrolysis of p-nitrophenolglycosides rather than the concentration of p-nitrophenolate. Somewhat surprisingly, the best inhibition was seen against beta-galactosidase with several of the compounds. The inositols linked through oxygen or nitrogen were subjected to calcium binding studies performed in NMR experiments. Detailed analysis of the title compounds by NMR spectroscopy has been performed, and full assignments were made. One of the attendant benefits of the preparation of these compounds has been expressed in the design and synthesis of new salen catalysts whose effectiveness has been compared with Jacobsen's catalyst in the epoxidation of styrene.

Calcium↗
PubMed2002

The synthesis and reactivity of a molybdenum (IV) stretched-dihydrogen complex.

Reaction of [Mo(NPh)(PMe3)3(o-(Me3SiN)2C6H4)] (1) with molecular hydrogen (ca. 1 atm) at -10 degrees C in toluene-d8 results in the formation of dihydrogen complex [Mo(NPh)(PMe3)2(H2)(o-(Me3SiN)2C6H4)] (2) by 1H and 31P NMR spectroscopy. In solution at -50 degrees C 1 and 2 are present in a 1:3 ratio, respectively. The nature of dihydrogen ligand bonding in 2 was probed by T1 analysis and analysis of the JH-D coupling constant in the deuterium hydride isotopomer of 2 giving H-H distances of 1.18 A and 1.17 A, respectively. When allowed to warm to 30 degrees C, 2 reacts affording [Mo(NPh)(PMe3)3(o-(Me3SiN)(NH)C6H4)] (3) over a 1 h period. The X-ray structures of 1 and 3 are reported.

Journal Article↗
PubMed2001

Tetracyclopropylmethane: A Unique Hydrocarbon with S(4) Symmetry This work was supported by the Fonds der Chemische Industrie. R.R.K. is grateful to the German Academic Exchange Service (DAAD) for a Research Fellowship, and A.P.M. to the European Union for a grant within the INTAS Program. The authors are indebted to Prof. Dr. P. von R. Schleyer and Dr. H. Jiao, Computer Chemistry Center of the Institut für Organische Chemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, for some initial computations on tricyclopropylmethane and tetracyclopropylmethane (7 a) as well as for their continuing interest in these investigations, and to Dr. B. Knieriem, Universität Göttingen, for his careful reading of the final manuscript.

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PubMed1999

Use of Electrochemical Methods as an Alternative to Tin Reagents for the Reduction of Vinyl Halides in Inositol Synthons.

Several vinyl halides previously used in inositol syntheses were subjected to electrochemical reduction. The unreactivity of allylic alcohols or allylic ethers at the applied potentials allowed the selective reduction of vinyl halides to olefins. Electrochemical methods provide for selective reduction of vinyl iodides over vinyl bromides, with better yields than analogous tin methodology. Cinnamyl ethers were reductively cleaved at -3.2 V (vs Ag/AgNO(3)) in the presence of alkyl allyl ethers to provide selective deprotection. The electrochemical reduction of vinyl halides in the presence of a vinyloxirane or vinylaziridine is accompanied by the solvolysis of the strained rings. Yields and conditions are reported and compared to those from standard tin-induced dehalogenation.

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PubMed1996

Efficient Syntheses of Substituted Carbazoles and Cyclopent[b]indoles from 1-Methyl-3-(benzotriazol-1-ylmethyl)indole.

1-Methyl-3-(benzotriazol-1-ylmethyl)indole (1) undergoes lithiation and 1,4-addition with a variety of alpha,beta-unsaturated ketones and aldehydes. Subsequent treatment with an acidic resin in refluxing 1,4-dioxane causes intramolecular cyclization followed by aromatization to furnish a wide range of 1,3-di-, 2,3-di-, and 1,2,3-trisubstituted carbazoles 6a-j and 8 in moderate to excellent yields. NMR study is described to discriminate between structures of types 6 and 8 on the basis of (1)H-(13)C long-range correlation. Treatment of 1 with styrenes in the presence of zinc bromide results in formal [3 + 2] cycloaddition to give cyclopent[b]indoles 14a-c in good yields. When 1 is first lithiated and reacts with electrophiles, the resulting alkylation products undergo similar [3 + 2] additions with styrenes to give 1-functionalized cyclopent[b]indoles 15 and 16with a high degree of stereoselectivity.

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