Borneol structure

The structure of the bicychc monoterpene borneol is shown in Figure 26 7 Isoborneol a stereoisomer of borneol can be prepared in the labora tory by a two step sequence In the first step borneol is oxidized to camphor by treatment with chromic acid In the second step camphor is reduced with sodium borohydride to a mixture of 85% isoborneol and 15% borneol On the basis of these transformations deduce structural formulas for isoborneol and camphor... 

The bornane-, camphane- and fenchane-type monoterpenes possess the [2.1.1] bicyclic skeleton formed by different cyclisation of the terpinyl cation. Important members include borneol 47, isobornyl acetate 48, camphene 49, camphor 50, fenchone 51 (Structure 4.12). 

Fluoroboric acid supported on silica (HBF4-silica) has recently been found to be a highly efficient catalyst in the protection of various functional groups. Structurally diverse alcohols, phenols, thiophenols, and anilines can be acylated under solvent-free conditions at room temperature.669 Even acid-sensitive tertiary alcohols (1-alkylcyclo-hexanols) and sterically hindered compounds, such as endo-borneol, give the acylated products in high yields. A triflic acid-silica catalyst also shows high activity in the (9-acetylation with Ac20 of alcohols and phenols.359... 

Less than 5% enantiomeric excess was obtained in the osmium-catalyzed oxyamination of 2-phenyl-l-propene when chiral carbamates derived from 1-menthol and 1-borneol were used96, but the structures of the resulting products were not reported. 

Dinuclear niobium sulfido and selenido dithiophosphates, Nb2Q4[S2P(OR)2]4,75,76 (Q = S, Se R = Et) (also xanthates and dithiocarbamates) have been prepared but no crystal structure was reported. Optically active chromium complexes, Cr[S2P(OR)2]3 derived from Z)-borneol and L-menthol, have been described.77... 

Figure 142. Solvent effects on the formation of helicate structures from a terpy strand. Head-to-tail double-stranded helicates obtained from borneol-terminated terpy ligands.

Compounds Containing the Bicyclo[2.2.1]heptane Structure 3.4.1. Camphor, Fenchone, Borneol, and Fenchol... 

Bromocamphor has been employed as the chiral starting material in an enantiospecific synthesis (ref. 146) which involved the formation of an indanone (CD moiety) related structurally to that used by Hoffmann-La Roche and led finally to (-)-estrone. Attempts to alkylate the a,p-unsaturated ketone with 2-(3-methoxyphenyl)ethyl iodide failed, not surprisingly, due to an elimination rather than the desired substitution reaction and accordingly the use of an a-methylenic derivative of the ketone and 3-methoxybenzyl chloride were obligatory. By the use of (-)-3-bromocamphor, which is readily available from (-)-borneol by oxidation to (-)-camphor and bromination, natural (+)-estrone could be obtained. 

The decrease of 65 and 66 excimer emission caused by the addition of (S)-borneol was observed with a series of organic compounds having different structures. Some steroidal compounds were particularly efficient in causing a decrease in excimer emission [216,217]. This result indicated that these functionalized CDs might be used as fluorescent sensors of organic molecules [218]. 

Photodimerization also proceed in y-CD derivatized with only one 9-substituted anthracene pendant at the primary rim. This results from the formation of 1 1 (host host) associated structures in which the two aromatic moieties are paired within the double CD hydrophobic pocket (Xass = 1.1 X 10 M" ). Inclusion of S-borneol causes dissociation of the complex and suppresses photodimerization. In anthracene-appended jS-CD, no photodimers are formed. Induced circular dichroism is consistent with a change of conformation of the host upon association of (S)-borneol [208]. 

With [Eu(dpm)3], 3,3-dimethylthietane 1 -oxide and DMSO gave 1 1 adducts, which had near perfect wedged octahedral structures, the Lewis bases occupying one of four equivalent positions of lowest symmetry. The species [M(dpm)3] (M = La, Pr, Eu, Er, Ho, or Lu) were monomeric in dry CCI4, and 1 1 adducts were formed with pyridine, borneol, and neopentanol. However, lanthanide shift reagents (L) could react with substrates (S) by a two-step mechanism, viz. 

Esters of 2-iodoxybenzoic acid (IBX-esters) 489 have been prepared by the hypochlorite oxidation of the readily available 2-iodobenzoate esters 488 (Scheme 2.139) and isolated in the form of stable microcrystalline solids [657,658], This procedure has been used for the synthesis of IBX-esters 489 derived from various types of alcohols, such as primary, secondary and tertiary alcohols, adamantanols, optically active menthols and borneol. Single-crystal X-ray data on products 489 revealed a pseudo-benziodoxole stmcture in which the intramolecular L--0 secondary bonds partially replace the intermolecular I - O secondary bonds, disrupting the polymeric structure characteristic of Phl02 and other previously reported iodylarenes [658], This stmctural feature substantially increases the solubility of these compounds in comparison to other iodine(V) reagents and affects their oxidizing reactivity. 

The structure of the bicyclic monoterpene borneol is shown in Figure 24.8. Isoborneol, a stereoisomer of borneol, can be prepared in the laboratory by a two-step sequence. 

More recent investigations of J. Read, W. Hiickel, H. Schmidt, W. Treibs, and V. Prelog were mainly devoted to disentangle the stereochemical structures of menthols, carvomenthols, borneols, fenchols, and pinocampheols, as well as the related ketones (see Gildemeister and Hoffmann, 1956). 

MS and proton NMR spectroscopy have mainly been used for structure elucidation of isolated compounds. However, there are some reports on mass spectrometric analyses of essential oils. One example has been presented by Griitzmacher (1982). The depicted mass spectrum (Figure 2.9) of an essential oil exhibits some characteristic molecular ions of terpenoids with masses at miz 136, 148, 152, and 154. By the application of a double focusing mass spectrometer and special techniques analyzing the decay products of metastable ions, the components anethole, fenchone, borneol, and cineole could be identi ed, while the assignment of the mass 136 proved to be problematic. 

The bicyclo[2.2.1]heptane cage is commonly known as the norbornyl system. This obscure name comes from a natural product, borneol, which has the structure shown in Figure 21.30, and comes from the camphor tree, common in Borneo. The prefixes syn and anti locate the direction of the OH or OTs group with respect to the double bond, and nor means no methyl groups. Thus, 7-hydroxybicyclo[2.2.1]hept-2-ene is 7-hydroxynorborn-2-ene, or, because there is only one possible place for the double bond, 7-hydroxy-norbornene. 

The catalytic efficiencies of ions of the first series of transition metals in the controlled Ce(IV) oxidation of borneol, isoborneol, and menthol do not follow the theoretically expected sequence. The rate order in absence of metal ions is borneol > isoborneol > menthol. The relative rates have been explained on the basis of structures, steric factors, and isomeric characteristics of the alcohols studied. ... 

The structure of a number of shift reagent adducts has been determined by X-ray crystallography. Similar structures were obtained for Ho(dpm)3. 2(4-methylpyridine)(Horrocks et al., 1971), and for Eu(dpm)3-2 pyridine (Cramer and Self, 1972). The lanthanide coordination sphere can be described as a square antiprism with the pyridine molecules occupying the apices of opposite square faces. For Lu(dpm)3-3-methylpyridine a structure that can be described as a capped trigonal prism has been obtained (Wasson et al., 1973). The relevance of these structures for NMR studies in solution is however not well established. A recent fluorescence study has shown that the Eu(dpm)3-2 pyridine system retains its solid state structure in solution (Catton et al., 1975). On the other hand considerable configurational lability was observed in the Eu(dpm)3-borneol... 

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