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1.
Konrad B. Becker 《Helvetica chimica acta》1977,60(1):94-102
The addition of water, acetic acid, and hydrogen bromide to the strained bridge-head olefins bicyclo[3.3.1]-1(2)-nonene (1) , bicyclo[4.2.1]-1(8)-nonene (2) , and bicyclo[4.2.1]-1(2)-nonene (3) gives exclusively the bridgehead alcohols, acetates, and bromides, respectively. The reaction rate constants for the addition of acetic acid to the bridgehead olefins 1,2 and 3 , and the solvolysis rates for the related 1-bromo-bicyclo[3.3.1]nonane (4) and 1-bromobicyclo[4.2.1]nonane (5) were measured. A comparison of the activation enthalpies of these two reactions gives an estimate of relative strain of the bridgehead double bond. The strain in the bicyclo[4.2.1]nonenes 2 and 3 is similar to that in trans-cyclooctene (8-9 kcal/mol). 相似文献
2.
Bentley TW Engels B Hupp T Bogdan E Christl M 《The Journal of organic chemistry》2006,71(3):1018-1026
A synthesis for the unsubstituted bicyclo[1.1.0]but-2-ylmethanols (endo- and exo-9) from 1,3-butadiene has been developed. Solvolyses of their sulfonates 10 and 11 took entirely different courses, as the endo compound 10 gave rise exclusively to rearranged products such as cyclopent-3-en-1-ol (14), while the exo compound 11 underwent only the substitution of the tosylate group with complete retention of the exo-bicyclo[1.1.0]but-2-ylmethyl skeleton. Under solvolytic conditions, 10 reacted at very similar rates to the corresponding monocyclic substrate, that is, cyclopropylcarbinyl mesylate (19); in contrast, 11 reacted only three times as fast as n-butyl tosylate and about 1000-fold slower than 10. The nature of the bicyclo[1.1.0]but-2-ylcarbinyl cations has been probed by quantum chemical calculations. Whereas, the exo isomer (exo-18) corresponds to a local energy minimum, the endo isomer is only a transition state [endo-18(TS)] for an automerization of the nonclassical cyclopent-3-en-1-yl cation (13) and converts into 13 by a Wagner-Meerwein rearrangement. The most favorable isomerization of exo-18 also leads to 13 but via a transition state resembling the 2-vinylcycloprop-1-yl cation [25(TS)]. On the introduction of methyl groups at positions 1 and 3 of exo-18, the cation is no longer an energy minimum and it becomes a transition state [27(TS)] for an automerization of the nonclassical 1,3-dimethylcyclopent-3-en-1-yl cation (28). The large effect of the methyl substitution rationalizes the puzzling results of the previous product and rate studies, which utilized various substituted derivatives of bicyclo[1.1.0]but-2-ylcarbinyl sulfonates as substrates. 相似文献
3.
Parent 1-silaadamant-1-yl (1+) and a series of mono-beta-silyl-substituted- (2-Me+, 2-F+, 2-Cl+, 2-Br+), bis-beta-silyl-substituted- (3-Me+), and tris-beta-silyl-substituted (4-Me+)-1-silaadamant-1-yl cations were studied by the DFT method at the B3LYP/6-31G(d,p) level and by GIAO NMR at the B3LYP/ 6-31G(d,p)//B3LYP/6-31G(d,p) level. The geometries, relative energies, NMR chemical shifts, and charge distribution in the bridgehead silylium ions are discussed and compared. The magnitude of the beta-silyl effect (the Si-C-Si+ hyperconjugation) is gauged as a function of structure. Related model studies on the silabicyclo[2.2.2]octyl (5+, 6+, 5a+, and 6a+), silanorbornyl (7+ and 8+), and silacyclohexyl cations (9+ and 10+) were carried out in which the effect of beta-silyl substitution on geometry, stability, and NMR chemical shifts was probed. The acyclic model Me3Si-CH2-Si+(Me)2 (11+) was used to gauge the influence of the twist angle between the p-orbital at Si+ and the C-Si bond on relative stability and on the changes in the 29Si NMR chemical shifts. Finally, interaction of 1+ with H2O and MeOH and 2-Me+ with H2O was also examined. The resulting optimized structures (12+, 13+, and 14+) and the computed NMR chemical shifts are most compatible with the formation of silaoxonium ions. 相似文献
4.
The INDO calculations were performed on three bridgehead alkyl radicals; bicyclo[1.1.1]pent-1-yl, bicyclo[2.1.1]hex-l-yl and bicyclo[2.2.1]hept-1-yl radicals. We have transformed the canonical molecular orbitals obtained by the INDO method into the localized molecular orbitals. With the use of the obtained localized molecular orbitals, the variation in the hyperfine coupling constant at the bridgehead proton in these radicals was pursued in terms of the through-bond (and/or the through-space) interaction according to the method by which we selectively can pick up a particular interaction between the specified localized molecular orbitals in a radical. As a result of this analysis, it was found that the hyperfine coupling constants in these radicals can be expressed by the summation of several terms; through-virtuals, through-space, through-bond, and some other coupling terms. 相似文献
5.
《Tetrahedron letters》1987,28(7):735-738
The bicyclo[3.3.1]nona-1(1),4(5)-diene (ZZ) ring system has been generated by intramolecular Diels-Alder cycloaddition of methyl 7-methylene-non-2-yn-8-enoate. This highly strained bridgehead diene undergoes a homo 1,5-hydrogen shift to yield a [3.3.1] propellane product. 相似文献
6.
Allen RN Shukla MK Burda JV Leszczynski J 《The journal of physical chemistry. A》2006,110(18):6139-6144
The geometries and energetics of complexes of Li(+), Na(+), K(+), Be(2+), Mg(2+), and Ca(2+)metal cations with different possible uric acid anions (urate) were studied. The complexes were optimized at the B3LYP level and the 6-311++G(d,p) basis set. Complexes of urate with Mg(2+), and Ca(2+)metal cations were also optimized at the MP2/6-31+G(d) level. Single point energy calculations were performed at the MP2/6-311++G(d,p) level. The interactions of the metal cations at different nucleophilic sites of various possible urate were considered. It was revealed that metal cations would interact with urate in a bi-coordinate manner. In the gas phase, the most preferred position for the interaction of Li(+), Na(+), and K(+) cations is between the N(3) and O(2) sites, while all divalent cations Be(2+), Mg(2+), and Ca(2+) prefer binding between the N(7) and O(6) sites of the corresponding urate. The influence of aqueous solvent on the relative stability of different complexes has been examined using the Tomasi's polarized continuum model. The basis set superposition error (BSSE) corrected interaction energy was also computed for complexes. The AIM theory has been applied to analyze the properties of the bond critical points (electron densities and their Laplacians) involved in the coordination between urate and the metal cations. It was revealed that aqueous solvation would have significant effect on the relative stability of complexes obtained by the interaction of urate with Mg(2+) and Ca(2+)cations. Consequently, several complexes were found to exist in the water solution. The effect of metal cations on different NH and CO stretching vibrational modes of uric acid has also been discussed. 相似文献
7.
The solvolysis rates and products of the 2-exo- norbornyl, bicyclo[3.2.1]oct-8-yl, bicyclo[3.3.1]non-2-yl, bicyclo[3.2.1]oct-6-yl, bicyclo[3.2.1]oct-2-yl and bicyclo[3.2.2]non-6-yl p-toluenesulfonates 10–15 , respectively, are reported. The exo/endo rate ratios for these epimeric secondary tosylates in 80% EtOH varied from 1125 for 11 to 1.6 for 15 . The relative rates varied between 2278 for exo- 10 and 4 ·10?3 for endo- 11 . The hydrolysis products were mainly rearranged alcohols and olefins. The unrearranged alcohols from the exo-tosylates were formed with complete or predominant retention of configuration, whereas those derived from the endo-tosylates were mostly inverted. These results confirm the hypothesis that relative rates, as well as products, are largely determined by the degree of bridging between the cationic center and a dorsal C-atom in the transition state and in the resulting ion pairs. Since bridging is a directed bonding interaction, it is subject to the same angle and conformational strains as ordinary covalent bonds. But bridging requires less geometrical change than the formation of normal bonds and of nonclassical ions. 相似文献
8.
9.
Abboud JL Castaño O Dávalos JZ Jiménez P Gomperts R Müller P Roux MV 《The Journal of organic chemistry》2002,67(4):1057-1060
The standard enthalpy of formation of gaseous 2-adamantyl chloride(2-Ad-Cl) was determined by calorimetric techniques. The standard Gibbs energy change for the chloride anion exchange between 1-adamantyl (1-Ad+) and 2-adamantyl (2-Ad+) cations in the gas phase was obtained by Fourier transform ion cyclotron resonance spectroscopy (FT ICR). Theoretical calculations at the G2(MP2) level were performed on these and other relevant species. This and data from the literature provided three highly consistent independent estimates of the relative stabilities of 2-Ad+ and 1-Ad+. This difference in gas-phase stability was compared to the differential structural effects on the rates of solvolysis of the corresponding chlorides and tosylates, and it was shown that the thermodynamic stability of the secondary cation is the leading factor determining the solvolytic reactivity of the precursors in the absence of solvent effects. Thus, under these conditions, the previously established linear free energy correlation between carbenium ion stability and solvolytic reactivity of bridgehead derivatives applies also to secondary derivatives. 相似文献
10.
Ulrich Burkert 《Journal of computational chemistry》1980,1(2):192-198
The energies of various conformations have been calculated by molecular mechanics for cis and trans isomers of 2,4,7,9-tetraoxabicyclo[4.4.0] decane and 3,5,8,10-tetraoxabicyclo[5.3.0]decane and their methyl derivatives. These molecules are models for reaction products from formaldehyde and the tetrols, pentitols, and hexitols. The conformational equilibria were analyzed for the cis-bicyclo [4.4.0] and cis-bicyclo[5.3.0] systems and compared with available experimental data. The thermodynamic stability of bicyclo[4.4.0] products was found to be higher than that of bicyclo[5.3.0] derivatives in the gas phase in every case studied. Discrepancies with experimental data that exist in a few cases can be ascribed to solvent effects. 相似文献
11.
Potentially trishomoaromatic cations possessing the 6-X-bicyclo[3.1.0]hex-3-yl (X = CH(2), BH, NH, O) or bicyclo[3.2.0]hept-3-yl unit have been investigated at the Hartree-Fock, second-order, third-order, and fourth-order (single, double, quadruple excitations) M?ller-Plesset perturbation level employing the 6-31G(d) basis set. IGLO/6-31G(d) chemical shift calculations have been carried out at optimized geometries. Through-space interactions between the symmetric Walsh orbital of the three-membered ring and ppi(C3) orbital have been analyzed as a function of orbital energies and orbital overlap. The best indicators for trishomoaromaticity are NMR chemical shifts and magnetic susceptibility. There is a simple relationship between the conformation of the trishomocyclopropenylium cation, its charge distribution, and delta(13)C3, which can be used to determine the conformation or the C1C3 interaction distance from NMR measurements. Trishomocyclopropylium cations investigated can rearrange to an envelope form of higher energy where the height of the inversion barrier and the chair-envelope energy difference are a measure for the homoaromatic stabilization energy. The bicyclo[3.1.0]hex-3-yl cation in its envelope form can rearrange with a barrier of just 1 kcal/mol to the bicyclo[3.1.0]hept-2-yl cation. In the case of the bicyclo[3.2.0]hept-3-yl cation, there exists just the envelope form, which can rearrange to a ethano-bridged center-protonated spirocyclopentyl cation. The later cation should be an interesting target of chemical synthesis since it contains a pentacoordinated carbon atom and possesses unusual properties. 相似文献
12.
The strained bridgehead olefins bicyclo [3.3.1]non-1-ene ( 1 ), bicyclo [4.2.1 ]non-1(8)-ene ( 2 ), and bicyclo [4.2.1]non-1-ene (3), and the comparable monocyclic (E)-1-methylcyclooctene ( 4 ) react with diphenylketene ( 6 ) to give a single cycloadduct 7 , 8 , 9 and 10 , respectively, in which the diphenyl-substituted C-atom is bound to the bridgehead. The structure of the cyclobutanone 8 has been determined by X-ray analysis of a twin crystal obtained by crystallization with spontaneous enrichment of enantiomers. 相似文献
13.
Filippi A Fraschetti C Renzi G Roselli G Speranza M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(30):7913-7919
The mechanism and stereochemistry of the intracomplex solvolysis of proton-bound complexes [Y...H...M]+ between M = CH3 (18)OH and Y = 1-arylethanol [(S)-1-(para-tolyl)ethanol (1S), (S)-1-(para-chlorophenyl)ethanol (2S), (S)-1-(meta-alpha,alpha,alpha-trifluoromethylphenyl)ethanol (3S), (S)-1-(para-alpha,alpha,alpha-trifluoromethylphenyl)ethanol (4S), (R)-1-(pentafluorophenyl)ethanol (5R), (R)-alpha-(trifluoromethyl)benzyl alcohol (6R), and (R)-1-phenylethanol (7R)] have been investigated in the gas phase (CH3F; 720 Torr) in the 25-140 degrees C temperature range. Gas-phase solvolysis of [Y...H...M]+ (Y=2S, 3S, 4S, and 7R) leads to extensive racemization above a characteristic temperature t(#) (e.g. at t(#)>60 degrees C for 7R), whereas below that temperature the reaction displays a preferential retention of configuration. Predominant retention of configuration is instead observed in the intracomplex solvolysis of [Y...H...M]+ (Y=1S, 4S, 5R, and 6R) with the temperature range investigated (25 相似文献
14.
用从头算HF/3-21+G^*优化了二氮双环[m,n,l]游离基阳离子(m,n,l≥2~5)。分子[4,4,4]和[2,2,2]^+.,[3,3,3]^+.,[4,4,4]^+.游离基阳离子的优势构型有D3对称性,而其它游离基阳离子的优势构型为非对称性。通过比较这些阳离子几何构型,HOMO和NHOMO(即NextHOMO和HOMO-1),和由MNDO计算确定的原子对作用能,表明当二氮双环游离基阳离子的桥链(CH2)n的n≥3时,桥头氮原子通过空间相互用用形成了一个弱的N,N'-三电子σ键。形成的三电子键强度不随环的扩大而增强。而三电子键强度被两个因素影响:一个是桥头氮原子间的p轨道重叠的取向;另一个是它们相应p轨道成分。 相似文献
15.
The 1H and 13C spectra of bicyclo[3.1.0]hexanes and thujanes have been recorded and assigned. Application of the Karplus equation has yielded dihedral angles, and a computer calculation of the angle of ring buckle as a function of the main dihedral angles has been carried out. The calculated angles of ring buckle agree well with known values in the bicyclo[3.1.0]hexanes, but for 1-methylbicyclo[3.1.0]hexanes and thujanes the results are not self consistent. It is suggested that the bridgehead substituent causes the boat to twist, although the twist can be reduced by an axial methyl substituent on C-4. 相似文献
16.
Tokunaga K Tachibana S Okazaki T Ohga Y Kitagawa T Takeuchi K 《The Journal of organic chemistry》2000,65(16):4964-4972
Methanolyses of 2-oxobicyclo[3.3.1]non-1-yl triflate, 3, 3-dimethyl-2-oxobicyclo[3.3.1]non-1-yl triflate, and 2-oxobicyclo[4. 3.1]dec-1-yl mesylate gave the corresponding propellanone in 12%, 20%, or 3.2% yield, respectively, beside substitution or rearranged products under typical conditions. No propellane-type product was obtained in the solvolyses of 1-bromobicyclo[3.3.1]nonane, 2-methylidenebicyclo[3.3.1]non-1-yl heptafluorobutyrate, and 3, 3-dimethyl-2-thioxobicyclo[3.3.1]non-1-yl tosylate. The factors that permit the formation of the propellane-type product from the intermediate bridgehead cations are examined with the aid of theoretical calculations at PM3 and B3LYP/6-31G. 相似文献
17.
Goldsmith RH Vura-Weis J Scott AM Borkar S Sen A Ratner MA Wasielewski MR 《Journal of the American Chemical Society》2008,130(24):7659-7669
A 4-(pyrrolidin-1-yl)phenyl electron donor and 10-cyanoanthracen-9-yl electron acceptor are attached via alkyne linkages to the bridgehead carbon atoms of bicyclo[2.2.2]octane and all three benzo-annulated bicyclo[2.2.2]octanes. The sigma-system of bicyclo[2.2.2]octane provides a scaffold having nearly constant bridge geometry on which to append multiple, weakly interacting benzo pi-bridges, so that the effect of incrementally increasing numbers of pi-bridges on electron transfer rates can be studied. Surprisingly, photoinduced charge transfer rates measured by transient absorption spectroscopy in toluene show no benefit from increasing the number of bridge pi-systems, suggesting dominant transport through the sigma-system. Even more surprisingly, the significant changes in hybridization undergone by the sigma-system as a result of benzo-annulation also appear to have no effect on the charge transfer rates. Natural Bond Orbital analysis is applied to both sigma- and pi-communication pathways. The transient absorption spectra obtained in 2-methyltetrahydrofuran (MTHF) show small differences between the benzo-annulated molecules that are attributed to changes in solvation. All charge transfer rates increase significantly upon cooling the MTHF solutions to their glassy state. This behavior is rationalized using combined molecular dynamics/electronic structure trajectories. 相似文献
18.
Activation of a bridgehead methyl group by the bicyclo[1.1.0]butyl moiety resulted in hydrogen abstraction by a photogenerated acetonyl radical, followed by a radical chain addition process. 相似文献
19.
Density functional theory calculations on complexes of 4C1, 1C4 and 2SO ring conformations of methyl beta-D-xylopyranoside 1 with divalent metal cations, M = Mg2+, Ca2+, Zn2+, and Cd2+, are presented. Bridging and pendant cationic, [M(H2O)41]2+ and [M(H2O)(5)1]2+, as well as neutral complexes, [M(OH)2(H2O)(2)1] and [M(OH)2(H2O)(3)1], and neutral complexes involving a doubly deprotonated sugar, [M(H2O)(4)1(2-)], are considered. In aqueous and chloroform solution the stability of cationic and pendant neutral complexes is greatly diminished compared with gas-phase results. In contrast, bridging neutral complexes [M(OH)2(H2O)(2)1] and those of type [M(H2O)(4)1(2-)], are stabilized with increasing solvent polarity. Solvation also profoundly influences the preferred binding position and ring conformation. Compared with complexes of bare metal cations, additional ligands, e.g., H2O or OH-, significantly reduce the stability of 1C4 ring complexes. Irrespective of the cation, the most stable structure of bridging complexes [M(H2O)(4)1]2+ results from coordination of the metal to O3 and O4 of methyl beta-D-xylopyranoside in its 4C1 ring conformation. 相似文献
20.
Mehdi Adib Sadegh Shabanibalajadeh Ehsan Sheikhi Mehdi Rahimi‐Nasrabadi Long‐Guan Zhu 《Helvetica chimica acta》2016,99(9):659-664
A one‐pot four‐component synthesis of 6‐aryl‐6H‐dibenzo[e,i][1,3,7,2]oxadiazaborecin‐8(7H)‐ones is described. Heating a mixture of isatoic anhydride and a benzylamine afforded the corresponding anthranilamide derivative, which was condensed with a 2‐hydroxybenzaldehyde and an arylboronic acid under solvent‐free conditions to produce bridgehead bicyclo[4.4.0]‐boron heterocycles in good to excellent yields. Single‐crystal X‐ray analysis conclusively confirms the structures of the obtained bridgehead bicyclic 6–6 heterocyclic compounds. 相似文献