Camphor assignment

The [2,3] Wittig rearrangement151 of the optically active tertiary allyl ether 10 derived from ( + )-camphor yields the two olefin products 11 and 12 in a 70 30 (EjZ) ratio. The configuration around the double bond was established by NOE studies. The configuration at the newly formed carbinol center could also have been determined by spectroscopic means, but was assigned by a correlation sequence (see p 475)152. 

Almgren has studied the emission spectra of o-anisil, benzil, and biacetyl in low temperature glasses containing varying amounts of isopropyl alcohol.105 Tsai and Charney have assigned the t n transitions of camphor-... 

Camphorate complexes of chromium (III) have been studied. The four possible isomers of the tris complex of (+ )-3-acetylcamphorate (173) were isolated,752,753 and absolute configurations were tentatively assigned. The photoisomerization of these complexes has been investigated 754 quantum yields of the order of 10-3 were obtained with visible or ultraviolet radiation at temperatures around 100 °C. Bond-breaking processes were held to be important in the reactivity of cis isomers. 

In accordance with the proportionality (3.8 a), the magnitude of the pseudocontact shift, which predominates for lanthanide shift reagents, decreases with the distance of nucleus i from the paramagnetic ion. Thus, C-9 of camphor is shifted more than C-10 on addition of the europium chelate. Often, the crude approximation (3.8 a) is a valuable assignment aid. 

A tremendous amount of work was done before the structure of camphor was successfully elucidated. Bredt (1893) was the first to assign the correct formula to camphor. The structure was confirmed by total synthesis, which was achieved by several authors. The most important aspects of this work are summarised (5) below ... 

The IR spectrum of camphor as KBr disc and Nujol mull were recorded on.a Perkin Elmber 58O B Infrared spectrophotometer to which Infrared data station is attached (Fig. 3). The structural assignments have been correlated with the following frequencies (Table 3). 

The PMR spectrum of camphor in CDCI3 was recorded on a Varian T-60A, 60 MHz NMR spectrometer using TMS (Tetramethylsilane) as an internal reference (Fig. b). The following structural assignments have been made... 

Our assignment of the methyl protons singlets is based on the anisotropy of the carbonyl function of camphor. The 9-methyl protons are falling within the deshielding zone of the carbonyl group and is expected to be the most lower field while C-10 methyl protons are away from the carbonyl function and is expected to suffer no deshielding effect. 

The enantiomeric purity of the bicyclic 3,6-dihydro-277-l,2-oxazine 3 was determined by H NMR of the D-camphor-10-sulfonyl derivative and was found to be >95%. The configuration of this compound was assigned by comparison with the reported optical rotation data, as (1 S,4R). This synthetic approach was utilized in the enantioselective synthesis of conduramine and streptamine analogs91. 

A review appeared on the practice and theory of enantioselective CGC with optically active selectors, e.g. 3-(perfluorobutyryl)-(17 )-camphorate residues forming complexes on a functionalized polysiloxane stationary phase (e.g. Chirasil, 65) SEC operates at temperatures lower than those of CGC, thus allowing better resolution, especially of thermally unstable enantiomers (e.g. those based on restricted free rotation, as is the case of dimethyl l,l -binaphthyl-2,2 -dicarboxylate, 66 ). Various analytical problems were addressed, such as determination of enantiomeric excess, assignment of absolute configuration, the elusive separation of protio- and deuterio-substituted enantiomers and the semipreparative separation of enantiomers. The following chromatographic parameters are related to the chemical and thermodynamic properties enclosed in parentheses of the enantiomeric system (i) peak retention (chemoselectivity, —AG), (ii) peak separation... 

Another sterically hindered alkene [e.g. (204)] (cf. Vol. 6, p. 40) has been synthesized, this time in diastereoisomeric forms, by reductive dimerization of (-t-)-camphor with LiAlH4-TiCl3-THF configurational assignments are consistent with the olefin octant rule. ... 

A limitation of the d/l system may be seen from the example of (+)-camphor (10), which was assigned configuration D. Comparison with the formula 3 for D-glyceraldehyde reveals that the inter-relationship is, at best, tenuous. Some suppliers still offer D-camphor for sale. 

The free base 3a was further converted to the mandelate salt, a white crystalline product. The cyclobutyl analog 3b was similarly prepared from 8 and converted to the crystalline mandelate salt. The (S ) A-tetrahydrofurfuryl derivative 3c was prepared from (S) tetrahydrofurfuryl (1/f) camphor-10-sulfonate (10) as previously reported (Mertz et al., 1997). The 10-keto morphinans were prepared by the oxidation (Michne and Albertson, 1972) of the morphi-nan 7 with Cr03/H2S04 followed by alkylation with cyclopropyl methyl bromide and 0-demethylation to yield 4b (Scheme 1). O-Demethylation of 11 to form 13 followed by alkylation with (S) tetrahydrofurfuryl (I R) camphor-10 sulfonate (10), led to 4a. The assignment of the stereochemistry of 4a was based on the work of Merz and Stockhaus (1979). 

---