Synthesis and conformation of some 2,4-dioxa- and 2,4-dioxa-3-silabicyclo[3.3.1]nonanes

The conformation of the title compounds established by ¹³C and ¹H NMR spectroscopy shows that replacement of the 2- and 4-methylene groups in bicyclo[3.3.1]nonane by ether oxygen atoms strongly destablizes the cc conformation: in 2-oxabicyclo[3.3.1]-nonane the cc and the bc conformers are about equally populated, whereas in 2,4-dioxabicyclo[3.3.1]nonane the bc conformation predominates. The 2,4-dioxa-3-silabicyclo[3.3.1]nonanes also occur predominantly inthe bc conformation. As in the carbocyclic bicyclo[3.3.1]nonanes both wings are strongly flattened. A stereoselective synthesis of 3-methylbicyclo[3.3.1]nonane, an important model compound in this study, is described.     

Conformational analysis of 3-borabicyclo[3.3.1]nonane derivatives

Conformations of 3-borabicyclo[3.3.1]nonane derivatives have been studied by means of ¹H and ¹³C NMR spectroscopy. With the aid of the coupling constants ³J(HH) and ¹³C chemical shifts it has been shown that all the derivatives of 3-borabicyclo[3.3.1]nonane with the trigonal boron atom studied are in a flattened double-chair conformation. In 3-borabicyclo[3.3.1]nonane derivatives with the tetra-coordinated boron atom and substituents at the 7α-position, the chair-boat conformation predominates, the boat conformation being characteristic of the cyclohexane ring; exceptions are the compounds with the internal donor—acceptor bond between the boron atom an 7α-substituent.     

13C NMR spectroscopy of some 3- and 7-substituted bicyclo[3.3.1]nonanes

The ¹³C NMR spectra of a series of 3,7-substituted bicyclo[3.3.1]nonane derivatives are examined. Taken into account substituent influences, the ¹³C chemical shifts appear to be diagnostic for the conformation of the bicyclo[3.3.1]nonane derivative.     

Stereochemical studies—XVIII : Conformational study of heteroanalogues of bicyclo[3.3.1]nonane

A number of heteroanalogues of bicyclo[3.3.1]nonane containing heteroatoms in 3-, 3,7- and 3,7,9-positions has been synthesized. ¹H NMR measurement has shown that the compounds of the types 4,5 and 6 (Y = oxygen) are double-chairs with the “wings” of the molecule flattened. However, a new conformational effect has been found for the sulfur containing compounds of type 5 and 6 (X,Y = sulfur) which show substantially increased tendency to adopt boat-chair conformations.     

13C-NMR-spektroskopische und stereochemische Untersuchungen: XI—Konformationen von Bicyclo[3.3.1]nonanen und ihre Unterscheidbarkeit durch lanthanideninduzierte Verschiebungen

The ¹³C chemical shifts of bicyclo[3.3.1]nonane and of the corresponding 9-hydroxy- and 9-oxo- derivatives are compared with chemical shifts calculated on the basis of stereospecific shift increments. These results as well as the ¹H n.m.r. spectrum of the ketone indicate a predominant chair-chair conformation CC. A low temperature ¹³C n.m.r. study as well as an analysis of the temperature dependence of ¹³C chemical shifts in bicyclo[3.3.1]nonane furnish a limit for the free energy difference between CC and BC conformations of ΔG ≧ 5,85 kJ mol^?1. The distinction between CC, BC and BB provides a test for the applicability of lanthanide-induced ¹H and ¹³C shifts for the assignment of flexible geometries. The typical occurrence of several and/or flat minima in the LIS geometry analysis allows only the exclusion of boat–boat conformations.     

Conformational behavior of 3-borabicyclo[3.3.1]nonanes: 1. Study of molecular dynamics in 3-methoxy-7α-phenyl-1,5-dimethyl-3-borabicyclo[3.3.1]nonane

3-Methoxy-7α-phenyl-1,5-dimethyl-3-borabicyclo[3.3.1]nonane 5 in solution at room temperature exists in the double chair conformation, as shown by NMR studies. Increasing the temperature leads to an increase in the population of the chair–boat conformation. At decreased temperature hindered rotation around the B---O bond is observed for 5. Dissolving 5 in deuteropyridine leads to the reversible formation of complex 6, which exists in the chair–boat conformation. The chair–boat conformation is also the most stable one for chelate compound 7 with a tetracoordinated boron atom.     

Lone pairs vs. covalent bonds: conformational effects in bicyclo[3.3.1]nonane derivatives

Structural Chemistry - Investigations on the relative energy of two least-strain conformers for bicyclo[3.3.1]nonane 1, bicyclo[3.3.1]nonan-9-one 2, and their heteroanalogues:...     

Solvolysis of 2-Bicyclo

The solvolysis rate of 2-bicyclo[3.2.2]nonyl p-toluenesulfonate (6-OTs) was nearly equal to that of cycloheptyl p-toluenesulfonate in 2,2,2-trifluoroethanol (TFE). This indicates that the ethylene bridge in 6-OTs does not significantly enhance the rate and that 6-OTs ionizes without anchimeric assistance. The solvolysis of [1-(13)C]-2-bicyclo[3.2.2]nonyl p-toluenesulfonate in methanol or TFE gave 2-substituted bicyclo[3.2.2]nonane, exo-2-substituted bicyclo[3.3.1]nonane, 2-bicyclo[3.2.2]nonene (10), and 2-bicyclo[3.3.1]nonene (11), whose distributions of (13)C labels were determined by quantitative (13)C NMR analysis using a relaxation reagent. The (13)C labels were exclusively placed at only two positions, the ratios of them were not unity, and the labels in 10 were less extensively scrambled than those in other products. These results indicate that the 2-bicyclo[3.2.2]nonyl cation is classical and that 10 is formed at a former ionization stage than 2-substituted bicyclo[3.2.2]nonane. The (13)C redistributions for both exo-2-substituted bicyclo[3.3.1]nonane and 11, which are yielded via 1,3-hydride shift, were similar to that of 2-substituted bicyclo[3.2.2]nonane, suggesting that 1,3-hydride shift occurs mainly at the solvent-separated ion pair.     

3,7-disubstituted bicyclo[3.3.1]nonanes—III: Synthesis and conformation of bicyclo[3.3.1]nonane-3α,7α-dicarboxylic acid,its dimethyl ester and some other 3,7-disubstituted bicyclo[3.3.1]nonanes; adamantane as an integrated holding system

The conformation of bicyclo[3.3.1]nonane-3α,7α-dicarboxylic acid and its dimethyl ester has been studied by comparing ¹H NMR and ¹³C NMR spectra of these compounds with those of some model 3,7-disubstituted bicyclo[3.3.1]nonanes, fixed in a single conformation by the use of adamantane as an integrated holding group or by means of suitable substitution. It is shown that the dicarboxylic acid and its dimethyl ester exist predominantly as two rapidly interconverting (identical) chair-boat conformations with distinctly flattened rings; the population of the double-boat conformation appears to be very small.     

13C and1H NMR spectra and structure of 2-aryl-1,3-dibenzoyl-1,3-diazabicyclo[3.3.1]nonanes

Conclusion ¹³C and¹H NMR spectroscopy was used to determine the structures of 2-aryl-1,3-dibenzoyl-1, 3-diazabicyclo[3.3.1]nonanes and 2-aryl-1-benzyl-3-benzoyl-1,3-diazabicyclo[3.3.1]nonane. These compounds were found to exist predominantly in the boat-chair conformation (boat for the diaza ring), while the 2-aryl substituents occupy the exo or endo position.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1023–1028, May, 1988.     

The "hockey sticks" effect revisited: the conformational and electronic properties of 3,7-dithia-1,5-diazabicyclo[3.3.1]nonane from the QTAIM perspective

The conformational effects in bicyclo[3.3.1]nonanes, while thoroughly studied, have not yet received the full theoretical explanation. R. F. W. Bader's quantum theory of atoms in molecules presents unique opportunities for studying the stereoelectronic interactions (SEI) and weak intramolecular bonding leading to these effects. Here, we report the study of 3,7-dithia-1,5-diazabicyclo[3.3.1]nonane by means of the topological analysis of the calculated (MP2(full)/6-311++G**) and experimental (X-ray derived) charge density to reveal the origins of the so-called "hockey sticks" effect observed in similar compounds. A new explanation of the relative stability of bicyclo[3.3.1]nonane conformers based on the analysis of the QTAIM atomic energies is given. The H···H and S···S interactions in bicyclo[3.3.1]nonane and its dithia derivatives are shown to be significant factors contributing to the differences in the relative stability of the conformers.     

Synthetic studies on phloroglucins: a new approach to the bicyclo[3.3.1]nonane system via the regioselective ring-opening of the methoxycyclopropane

A new synthetic approach to the bicyclo[3.3.1]nonane system, a common structure in a number of polyisoprenylated phloroglucinol derivatives (phloroglucins), has been developed. The key step in our approach is a ‘one-pot’ procedure of two successive reactions, the intramolecular cyclopropanation reaction which affords the tricyclo[4.4.0.0^5,7]dec-2-ene derivative and its methoxy group directed regioselective ring-opening reaction mediated by ZnCl₂, producing the desired bicyclo[3.3.1]nonane as the sole product.     

13C NMR spectra of bicyclo[3.3.1]nonanones and their derivatives

Conclusions An assignment was made of the lines in the¹³C NMR spectra of the mono- and diketones of the bicyclo[3.3.1]nonane series, and of the hydrolysis products of bicyclo[3.3.1]nonane-2,9-dione and its 7-benzoyloxy derivative.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2386–2389, October, 1979.     

Synthesis of novel piperazine based building blocks: 3,7,9-triazabicyclo[3.3.1]nonane, 3,6,8-triazabicyclo[3.2.2]nonane, 3-oxa-7,9-diazabicyclo[3.3.1]nonane and 3-oxa-6,8-diazabicyclo[3.2.2]nonane

The preparation of four novel bridged piperazine building blocks is described: 3,7,9-triazabicyclo[3.3.1]nonane 1, 3-oxa-7,9-diazabicyclo[3.3.1]nonane 2, 3,6,8-triazabicyclo[3.2.2]nonane 3 and 3-oxa-6,8-diazabicyclo[3.2.2]nonane 4. The scaffold of 1 was synthesized from N,N′-dibromobenzenesulfonamide and ethyl acrylate. Compound 2 may be prepared from identical starting materials or alternatively from α,α′-diglycerol. Compounds 3 and 4 were identified as side products from possible aziridinium intermediates.     

3-Azabicyclo[3.3.1]nonane Derivatives: IX. Synthesis and Molecular Structure of 3-Azabicyclo[3.3.1]nonane-1,5-diamines in Solution and in Solid State

During catalytic reduction with hydrogen on nickel of a series of 3-substituted 1,5-dinitro-3-azabicyclo-[3.3.1]non-6-enes alongside nitro groups reduction occurred also hydrogenation of the double bond. New diamines of the 3-azabicyclo[3.3.1]nonane series were synthesized, and their structure was established by means of IR, ¹H and ¹³C NMR spectroscopy and X-ray diffraction study.     

Spectroscopic study of 3-methyl-2,4-diphenyl-3-azabicyclo[3.3.1]nonan-9-α(β)-ols

3-Methyl-2,4-diphenyl-3-azabicyclo[3.3.1]nonan-9-α(β)-ols have been synthesized and studied by ir, ¹H and ¹³C nmr spectroscopy. In deuteriochloroform and perdeuteriobenzene solutions, these compounds adopt a flattened chair-chair conformation in which the cyclohexane ring is more flattened. From the ¹H and ¹³C nmr data, several stereoelectronic effects have been deduced. The complete and unambiguous assignment of all protons of the 3-azabicyclo[3.3.1]nonane system, not described up to date, has been carried out.     

Structure elucidation with lanthanide induced shifts. 9. bicyclo[3.3.1]nonan-9-one

Lanthanide shift reagents have been used for the conformational analysis of bicyclo[3.3.1]-nonan-9-one. Comparison of predicted shifts and experimental values obtained with Eu(fod)₃ indicate that the boat-chair conformation constitutes 22% of the mixture of conformers.     

Synthesis, structural and crystallographic study of some carbamates derived from 9-methyl-9-azabicyclo[3.3.1]nonan-3α-ol

A series of benzimidazole, thiazole and benzothiazole carbamates derived from 9-methyl-9-azabicyclo[3.3.1]nonan-3α-ol was synthesized and studied by ¹H, ¹³C, 2D NMR and IR spectroscopy. To assist in the interpretation of the spectroscopic data, the crystal structure of 3 (9-methyl-9-azabicyclo[3.3.1]nonan-3α-yl 2-amino-1H-benzimidazole-1-carboxilate) was determined by X-ray diffraction. It has been found that 1-carbamates and 2-carbamates can be obtained in the case of the benzimidazole derivatives. The benzimidazole-1-carbamates are obtained in higher yields (41, 38%) than the benzimidazole-2-carbamates (3, 9%). The compounds studied displayed in CDCl₃ solution a preferred chair–boat conformation with the substituted ring in a distorted boat form and the N–CH₃ substituent in an axial position with respect to the chair piperidine ring. This conformation is similar to that determined by X-Ray diffraction for compound 3.     

Conformational effects of 1,5,9-substitution in symmetric bicyclo[3.3.1]nonane analogues

The high-level ab initio calculations on several derivatives of bicyclo[3.3.1]nonane, 1-aza- and 1,5-diazabicyclo[3.3.1]-nonanes show the ‘double chair’ (CC) conformer as optimal for all of them, dominating over the ‘boat–chair’ (BC) form. Conformational effects of several substitution types involving positions 1, 5 and 9 are quantified, and their values are found rather transferable.     

Electrophilic Additions to Strained Bridgehead Olefins. Estimation of Strain by Comparison with the Solvolysis of Bridgehead Bromides

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).