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Proton Sponges (proton + sponge)
Selected Abstracts1,8-Bis(dialkylamino)-4,5-dinitronaphthalenes and 4,5-Bis(dimethylamino)naphthalene-1,8-dicarbaldehyde as "Push,Pull" Proton Sponges: When and Why Formyl Groups Become Stronger ,-Electron Acceptors than Nitro GroupsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2009Valery A. Ozeryanskii Abstract Single-crystal X-ray studies of four representatives of "push,pull" proton sponges, namely 1,8-bis(dimethylamino)-, 1,8-bis(diethylamino)-, 1,8-bis(dipropylamino)-4,5-dinitronaphthalenes and 4,5-bis(dimethylamino)naphthalene-1,8-dicarbaldehyde have been performed at low and ambient temperatures. The most interesting and unexpected result is that the formyl groups in the peri -dialdehyde display stronger ,-acceptor effects than the nitro groups. This phenomenon is ascribed to smaller steric demands of the CHO groups, their lower electrostatic repulsion, and specific packing forces. The naphthalene cores of all but one of the molecules are markedly twisted (21,26°) while that of the diethylamino derivative is not (<5°), providing different and somewhat unpredictable ways of resonance stabilization and steric relaxation. The through-conjugation in the above compounds is also discussed for gas and solution phases on the basis of theoretical calculations, UV/Vis and 1H NMR spectra.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] ChemInform Abstract: Binaphthyl Substituted 1,8-Bis(dimethylamino)naphthalenes, the First Chiral, Atropisomeric, Proton Sponges.CHEMINFORM, Issue 42 2008Jean-Paul Mazaleyrat Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Metal-Promoted Cage Rearrangements in the Tricarbollide Series: Conversion of Ligand Derivatives 7-L- nido -7,8,9-C3B8H10 (L = H3N, tBuH2N, Me2HN) into Neutral 8-R- nido -7,8,9-C3B8H11 (R = H2N, tBuHN, Me2N) CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2003Bohumír Grüner Abstract Deprotonation of the eleven-vertex tricarbaborane zwitterions 7-L- nido -7,8,9-C3B8H10 [1: L = H3N (1a), tBuH2N (1b), Me2HN (1c)], followed by reactions with metal reagents [FeI2, NiCl2, and Ni(C5H5)2] at higher temperatures and in situ acidification, led to the 7 , 8 rearrangement of the N -substituted cage carbon atom to yield a series of 8-amino-substituted derivatives of nido -7,8,9-C3B8H12. These were characterized as 8-R- nido -7,8,9-C3B8H11 [2: R = H2N (2a), tBuHN (2b), Me2N (2c)]. A possible rearrangement mechanism for their formation has been proposed. Deprotonation of compound 2a with proton sponge [PS = 1,8-bis(dimethylaminonaphthalene)] generated the [8- tBuHN- nido -7,8,9-C3B8H10], (2b,) anion, which can be reprotonated to give the original compound 2b and not the tautomeric zwitterion 8- tBuH2N- nido -7,8,9-C3B8H10 (3b). All compounds were characterized by high-field (11B and 1H) NMR and IR spectroscopy, and mass spectrometry. The molecular structures of the neutral carbaborane 2b and its salt PSH+2b,were determined by single-crystal X-ray diffraction analyses. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Reactions of Methyl Diazoacetate with (E)- and (Z)-1,2-Bis(trifluoromethyl)ethene-1,2-dicarbonitrile: Novel and Unanticipated Pathways,HELVETICA CHIMICA ACTA, Issue 1 2007Rolf Huisgen Abstract The cycloadditions of methyl diazoacetate to 2,3-bis(trifluoromethyl)fumaronitrile ((E)- BTE) and 2,3-bis(trifluoromethyl)maleonitrile ((Z)- BTE) furnish the 4,5-dihydro-1H -pyrazoles 13. The retention of dipolarophile configuration proceeds for (E)- BTE with >,99.93% and for (Z)- BTE with >,99.8% (CDCl3, 25°), suggesting concertedness. Base catalysis (1,4-diazabicyclo[2.2.2]octane (DABCO), proton sponge) converts the cycloadducts, trans - 13 and cis - 13, to a 94,:,6 equilibrium mixture (CDCl3, r.t.); the first step is N -deprotonation, since reaction with methyl fluorosulfonate affords the 4,5-dihydro-1-methyl-1H -pyrazoles. Competing with the cis/trans isomerization of 13 is the formation of a bis(dehydrofluoro) dimer (two diastereoisomers), the structure of which was elucidated by IR, 19F-NMR, and 13C-NMR spectroscopy. The reaction slows when DABCO is bound by HF, but F, as base keeps the conversion to 22 going and binds HF. The diazo group in 22 suggests a common intermediate for cis/trans isomerization of 13 and conversion to 22: reversible ring opening of N -deprotonated 13 provides 18, a derivative of methyl diazoacetate with a carbanionic substituent. Mechanistic comparison with the reaction of diazomethane and dimethyl 2,3-dicyanofumarate, a related tetra-acceptor-ethylene, brings to light unanticipated divergencies. [source] The Stereostructure of Porphyra-334: An Experimental and Calculational NMR Investigation.HELVETICA CHIMICA ACTA, Issue 3 2007Evidence for an Efficient, Proton Sponge' Abstract The mycosporine-like amino acid (MAA) porphyra-334 (1) is subjected to extensive 1H- and 13C-NMR analysis as well as to density-functional-theory (DFT) calculations. All 1H- and 13C-NMR signals of 1 are assigned, as well as the resonances of prochiral proton pairs. This is achieved by 500-MHz standard COSY, HMQC, and HMBC experiments, as well as by one-dimensional (DPFGSE-NOE) and two-dimensional (NOESY) NOE experiments. Diffusion measurements (DOSY) confirm that 1 is monomeric in D2O solution. DFT Calculations yield 13C-NMR chemical shifts which are in good agreement for species 6 which is the imino N-protonated form of 1. An exceptionally high proton affinity of 265.7,kcal/mol is calculated for 1, indicating that 1 may behave as a very powerful ,proton sponge' of comparable strength as synthetic systems studied so far. Predictions of 13C-NMR chemical shifts by the ,NMRPredict' software are in agreement with the DFT data. The absolute configuration at the ring stereogenic center of 1 is concluded to be (S) from NOE data as well as from similarities with the absolute configuration (S) found in mycosporine-glycine 16. This supports the assumption that 1 is biochemically derived from 3,3- O -didehydroquinic acid (17). The data obtained question the results recently published by a different research group claiming that the configuration at the imino moiety of 1 is (Z), rather than (E) as established by the here presented study. [source] 1,8-Bis(dialkylamino)-4,5-dinitronaphthalenes and 4,5-Bis(dimethylamino)naphthalene-1,8-dicarbaldehyde as "Push,Pull" Proton Sponges: When and Why Formyl Groups Become Stronger ,-Electron Acceptors than Nitro GroupsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2009Valery A. Ozeryanskii Abstract Single-crystal X-ray studies of four representatives of "push,pull" proton sponges, namely 1,8-bis(dimethylamino)-, 1,8-bis(diethylamino)-, 1,8-bis(dipropylamino)-4,5-dinitronaphthalenes and 4,5-bis(dimethylamino)naphthalene-1,8-dicarbaldehyde have been performed at low and ambient temperatures. The most interesting and unexpected result is that the formyl groups in the peri -dialdehyde display stronger ,-acceptor effects than the nitro groups. This phenomenon is ascribed to smaller steric demands of the CHO groups, their lower electrostatic repulsion, and specific packing forces. The naphthalene cores of all but one of the molecules are markedly twisted (21,26°) while that of the diethylamino derivative is not (<5°), providing different and somewhat unpredictable ways of resonance stabilization and steric relaxation. The through-conjugation in the above compounds is also discussed for gas and solution phases on the basis of theoretical calculations, UV/Vis and 1H NMR spectra.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] | ||||||||||