J. M. Van Der Toorn

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

Abstract The conformation of bicyclo[3.3.1]nonane-3α,7α-dicarboxylic acid and its dimethyl ester has been studied by comparing 1 H NMR and 13 C 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.

Chair-boat equilibria in bicyclo[3.3.1]nonane and some 3- and 3,7-substituted derivatives: Thermodynamic parameters and geometry of the conformers as obtained by molecular mechanics

Abstract ΔG-Values for conformational equilibria in 3,7-substituted bicyclo[3.3.1]nonanes have been obtained by means of epimerisation experiments ( cc α bc ) and by variable temperature 13 C NMR ( bc α bb ). The results of these experiments fit well with those of molecular mechanics using the Schleyer force field. In bicyclo[3.3.1]nonane and 3β-substituted derivatives the cc conformation predominates; however, the bulky 3β-substituent t-butyl, is found to have a destabilizing effect. A 3α-substituent forces the substituted wing into the boat conformation. For the 3α,7α-substituted derivatives the conformational preferences depend on the size of the substituents: for 3α-methyl-7α-t-butylbicyclo[3.3.1]nonane the cb and t- bb conformers are of approximately equal enthalpy. The geometries, obtained by the calculations, show that the conformers of bicyclo[3.3.1]nonane ( cc , bc and t-bb ) are all distinctly flattened. The boat wings of bc conformers are not twisted to any extent. The t-bb is the most stable bb conformation. The influence of substitution at positions 3 or 7 is discussed in detail; in general, a bulky substituent such as t-butyl, affects the geometry of both wings of the ring system. The calculated geometries are in good agreement with the conclusions of previous 1 H NMR investigations.

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

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

Impurities in Illicit Amphetamine

Reference is made to a peculiar compound, accidentally obtained in the reductive animation of benzyl methyl ketone. The product appears to be degraded by mild heating into cis- and trans-1,5-diphenyl-2-methyl-4-oxopentene-1 and cis- and trans-1,5-diphenyl-2-methyl-4-oxopentene-2, (the structures of which were established by low- and high-resolution mass spectrometry and by 1 H NMR spectroscopy). By means of proton exchange experiments and 1 H NMR spectroscopy the structure of the original compound 2,4-dihydroxy-l,5-diphenyl-4-methyl-pentene-l was found. The structure of a further compound, occurring in minor quantities, 3,4-dihydro-2-benzyl-2-methyl-4-oxo-5-phenyl-2H pyrrole, was established by the same spectroscopic methods. A plausible, but in no way substantiated, route to this compound is suggested.

Conformational analysis of 7-alkyl-3-oxabicyclo-[3.3.1]nonanes and complexes with lanthanide shift reagents

Abstract The conformation of 3-oxabicyclo[3,3.1]nonane and of some of its 7α- and 7β-alkyl substituted derivatives has been studied with the use of 13C and 1H NMR spectroscopy. A comparison is made with the carbocyclic analogues; it turns out that the replacement of the 3-methylene group by oxygen has no substantial influence on the conformational preferences. With the aid of 3JHH coupling constants it is shown that the geometry of the cyclohexane rings is about the same as in the corresponding carbocyclic compounds. The results of calculations on the lanthanide induced shifts indicate that the tetrahydropyran ring is not flattened but probably somewhat puckered. The calculated location of Eu(III) in complexes of Eu(dpm)3 with the 3-oxabicyclo [3.3.1]nonanes is compared with that in the complexes of the related compounds 2-oxaadamantane and 4-methyltetrahydropyran. The data indicate that the lanthanide ion coordinates “axially” to the latter compound.

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

Abstract The conformation of the title compounds established by 13 C and 1 H 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 3α-methylbicyclo[3.3.1]nonane, an important model compound in this study, is described.

Dynamic behaviour in (1′-t-butyl-2′,2′-dimethylpropyl)-π- (tricarbonylchromium)benzene

The temperature dependence of the 1H NMR spectrum of the title compound was studied over the temperature range 0–115° C. Two conformers were detected. The conformational isomerism is caused by a restricted rotation about the bond between the alkyl group and the complexed aromatic ring. The gDG≠ value for the interconversion amounts to 16.9 kcal mol−1, which is substantially smaller than the corresponding ΔG≠ value for the free ligand. This decrease is ascribed to additional steric strain between the alkyl and the tricarbonylchromium groups in the conformers of the complex.