Camphor stereochemistry

This contrary stereochemistry in the Bucherer - Bergs reaction of camphor has been attributed to steric hindrance of e.w-attack of the cyanide ion on the intermediate imine. Normally, equatorial approach of the cyanide ion is preferred, giving the axial (t>Mr/o)-amino nitrile by kinetic control. This isomer is trapped under Bucherer-Bergs conditions via urea and hydan-toin formation. In the Strecker reaction, thermodynamic control of the amino nitrile formation leads to an excess of the more stable compound with an equatorial (e.w)-amino and an axial (endo)-cyano (or carboxylic) function13-17. 

Fry and Newberg 1,2> examined the electrochemical reduction of nor-camphor oxime (109) and camphor oxime (110) to the corresponding amines. The results of this study are shown in Table 3. It is clear from a comparison of these data with those in Table 2 that the electrochemical reduction of oximes 109 and 110 takes a very different stereochemical course from reduction of the corresponding anils 103 and 104. Reduction of oximes apparently proceeds under kinetic control, affords products corresponding to protonation at carbon from the less hindered side of the carbon-nitrogen double bond, and affords the less stable epimeric amine in each case. It is not evident why the stereochemistry of reduction of anils and oximes should differ, however. 

Studies of the intramolecular cyclization of P-amino acids have included the use of camphor-derived oxazoline A-oxide 66 and a [3+2] cycloaddition reaction as a step in the formation of the amino acid with the required stereochemistry <00OL1053, OOEJOC1595>. A diastereoselective synthesis of a ip-methylcarbapenem intermediate utilises a cyclization of a P-amino acid <99CC2365>. 

Camphor sultam derivatives have proved to be effective chiral auxiliaries in many different types of asymmetric reactions. As shown in Scheme 5-44, chiral camphor sulfam can be applied in the synthesis of (—)-pulo upone precursor 151 using an intramolecular Diels-Alder reaction. A Wittig reaction of 148 with 147 connects the chiral auxiliary to the substrate, and subsequent intramolecular Diels-Alder reaction via transition state 150 affords product 151. Compound 151 already has the stereochemistry of (—)-pulo upone 153.72... 

In 1895, Armstrong published some twenty-five papers jointly with members of his chemical laboratory. A report to the alumni in 1903 mentions work in five subjects undertaken by Armstrong and some of his proteges radioactivity (H. Armstrong and Lowry), dynamic isomerism (Lowry), stereochemistry of noncarbon elements (Pope), the chemistry of camphor (M. O. Forster), and tautomerism (Lapworth).34... 

In 1815 Biot12) recognized that certain liquid organic compounds and also the solutions of some solid substances like saccharose, camphor, and tartaric acid are capable of rotating the plane of linearly polarized light. He ascribed this to some inherent property of the compound molecules. This initiated a development which led to the concept of stereochemistry. 

Electrochemical reduction of camphor-and norcamphoroxime at a Hg cathode proceeds with a high degree of stereoselectivity to give products of opposite stereochemistry to those formed in the dissolving metal (Na-alcohol) reduction of the oximes. The electrolyses are proposed to proceed by a kinetically controlled attack by the electrode on each oxime from the less hindered side (Fig. 62) [348]. In contrast, the corresponding N-phenyl imines yield products of the same stereochemistry as those isolated from a dissolving metal reduction. Cyclic voltammetry and polarographic data point to RH and intermediates in this case that are proto-nated from the least hindered side [349]. 

Electrochemical reductions of camphor oxime (R = Me) and norcamphor oxime (R = H) at a mercury cathode proceed with a high degree of diastereoselectivity (equation 3) . The products are in fact of opposite stereochemistry to those formed in dissolving metal (sodium-ethanol) reductions of the oximes. 

Wynberg studied stereochemistry of the McMurry reductive dimerization of camphor in detail (64). In Scheme 37, A and B are homochiral dimerization products derived by the low-valence Ti-promoted reduction, while C and D are achiral heterochiral dimers. The reaction of racemic camphor prefers homochiral dimerization (total 64.9%) over the diastereomeric heterochiral coupling (total 35.1 %). Similarly, as illustrated in Scheme 38, oxidative dimerization of the chiral phenol A can afford the chiral dimers B and C (and the enantiomers) or the meso dimer D. In fact, a significant difference is seen in diastereoselectivity between the enaritiomerically pure and racemic phenol as starting materials. The enantiomerically pure S substrate produces (S,S)-B exclusively, while the dimerization of the racemic substrate is not stereoselective. In the latter case, some indirect enantiomer effect assists the production of C, which is absent in the former reaction. Thus, it appears that, even though the reagents and reaction conditions are identical, the chirality of the substrate profoundly affects the stability of the transition state. 

The stereochemistry of camphor is well summarised by Finar and Pinder (5,8,9). 

Allen and Rogers (18) have redetermined the crystal structure of (+)-3-bromocamphor to elucidate its absolute stereochemistry and which is known to have the same stereochemistry of (+)-camphor. The determination was achieved by the use of new three dimensional x-ray data. 

Incorporation of the thiabutadiene moiety into a camphor framework resulted in the reaction with various dienophiles proceeding with complete Jt-facial selectivity and, in some instances, exo-selectivity. The stereochemistry of one product was confirmed by X-ray analysis. The (arylmethylene)thiocamphor compounds 429 were prepared by thionation of the corresponding ketones with Lawesson s reagent and exist as stable monomers (Equation 125) <1999TL8383>. 

Cathodic reduction of camphor and norcamphor oxime 144a appears to be cases where the stereochemistry is controlled by attack by the electrode from the least hindered side of the molecule ... 

An understanding of the three-dimensional structures of molecules has played an important part in the development of organic chemistry. The first experiments of importance to this area were reported in 1815 by the French physicist J. B. Biot, who discovered that certain organic compounds, such as turpentine, sugar, camphor, and tartaric acid, were optically active that is, solutions of these compounds rotated the plane of polarisation of plane-polarized light. Of course, the chemists of this period had no idea of what caused a compound to be optically active because atomic theory was just being developed and the concepts of valence and stereochemistry would not be discovered until far in the future. 

Because the bridge holds the molecule in a fixed conformation, the cleaved diacid has to have a specific stereochemistry. There is no change at the stereogenic centres, so the reaction must give retention of configuration. We can confidently write the structure of camphoric acid with ris-CC H groups, but any doubt is dispelled by the ability of camphoric acid to form a bridged bicyclic anhydride. 

Society, the Royal Society of Chemistry, and Ncue Schweizerische Chemische Gesellschaft. We have also updated the cross references to our main book to be consistent with the recently published second edition, and have corrected the absolute stereochemistry of camphor. We are grateful to Debbie Crans, Guella Graziano and Brian Mann for copies of their spectra, and Mike Springett for more lettering and pasting. 

The importance of the ethylene ketal described above with respect to stereocontrol of the de-Mayo reaction is emphasized by later published works of two other teams. Fetizon and co-workers obviously followed a similar concept and carried out photocycloaddition reactions with 96a in model studies (Scheme 23) (Si). As can be seen from retroaldol product 98, exclusive a attack of the cyclohexene has taken place. Thus, the relative stereochemistry of the BC ring connection is opposite to that of taxane. Totally comparable results were obtained by Berkowitz et al. in the course of cycloaddition reactions of cyclopentene, cyclohexene, or those of a cyclohexenone ketal to the camphor derivative 96b (.84). 

As a sequel to the elegant and highly efficient synthesis of camphor by an intramolecular cyclization. Money et have successfully applied this method to the synthesis of the naturally-occurring sesquiterpenoids campherenone (110) and campherenol (111) whose structures and absolute stereochemistries have recently been deduced.In this sequence, dihydrocarvone (112) was readily converted into the keto-ketal (113) from which the homologated chloro-ketone (114) was obtained. Treatment of the corresponding enol acetate (115) with boron trifluoride in wet methylene chloride afforded the two bicyclic chloro-ketones (116) and (117) in 55-60% yield. Conversion of the corresponding iodo-ketals... 

Gelb, M. H., Heimbrook, D. C., Malkonen, P., and Sligar, S. G. Stereochemistry and deuterium isotope effects in camphor hydroxylation by the cytochrome P450cam monoxygenase system. Biochemistry 21, 370-377 (1982). 

Nucleophilic addition reactions occur by electron donation from the nucleophile to the IT antibonding orbital of the ketone. If the faces of the ketone are different, addition happens faster at the more accessible orbital lobe. Use SpartanView to display mesh electron-density surfaces of 2-norbomanone and camphor, and simultaneously display the tt antibonding orbital (LUMO) surface of each. Which face of each ketone is more reactive What is the stereochemistry of the alcohol produced by reaction of each with NaBH4 ... 

The reaction of CH acidic compounds with CS2 in the presence of excess base yields dianions of dithiocarboxylic acids. Starting from camphor, neutralization with HCl and addition of primary amines yields 3-oxonorbomanethiocarboxamides (11) with undefined stereochemistry (Scheme 3). ... 

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