Of camphor derivative

Ordinary commercial camphor is (-i-)-cam phor, from the wood of the camphor tree. Cinnamonum camphora. Camphor is of great technical importance, being used in the manufacture of celluloid and explosives, and for medical purposes, /t is manufactured from pinene through bornyl chloride to camphene, which is either directly oxidized to camphor or is hydrated to isoborneol, which is then oxidized to camphor. A large number of camphor derivatives have been prepared, including halogen, nitro and hydroxy derivatives and sulphonic acids. 

Since cbiral sulfur ylides racemize rapidly, they are generally prepared in situ from chiral sulfides and halides. The first example of asymmetric epoxidation was reported in 1989, using camphor-derived chiral sulfonium ylides with moderate yields and ee (< 41%) Since then, much effort has been made in tbe asymmetric epoxidation using sucb a strategy without a significant breakthrough. In one example, the reaction between benzaldehyde and benzyl bromide in the presence of one equivalent of camphor-derived sulfide 47 furnished epoxide 48 in high diastereoselectivity (trans cis = 96 4) with moderate enantioselectivity in the case of the trans isomer (56% ee). ... 

The lithiation and hydroxyalkylation of camphor-derived A-benzylimines proceeds with medium-induced stereoselectivity15 16. 

A rich family of 2-alkoxycarbonyl-l,3,2-oxazaphospholidine-2-oxides 179-181 was prepared from the reaction of camphor derived aminoalcohols 177 and 178 with either methoxycarbonyl phosphonic dichloride or ethyl dichlorophosphite followed by the reaction with methyl bromoacetate. The reaction with aminoalcohol 177a afforded the phosphorus epimers 179 and 180, in ratios from 1/1 to 12/1 depending on the iV-substituent which could be separated easily by column chromatography. The reaction with aminoalcohols 178a-c, however, gave a single epimer 181a-c in each case (Scheme 50) [81]. 

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>. 

The synthesis of camphor-derived nitrones (87), of spin traps containing alkyl-phenylphosphoryl (36a,b) (88) and diethoxyphosphoryl substituents (37-39) requires m-CPBA as an oxidant (Fig. 2.3) (89, 90). 

Knochel and coworkers synthesized a series of camphor-derived pyridine and quinoline P,N ligands. The catalysts 30 (Fig. 29.17) were used to hydrogenate substrates 1 and 2 in up to 95% and 96% ee, respectively [33]. The selectivities were moderate for other unfunctionalized alkenes however, a high enantioselec-tivity was reported for the hydrogenation of ethyl acetamidocinnamate 10 [34]. 

Evans et al. (34) reported preliminary results showing that 55c CuOTf is moderately selective in mediating the aziridination of styrene, producing the heterocycle in 61% ee. Lowenthal and Masamune (44) mention in a footnote to their cyclopropanation paper that the copper complex of camphor-derived bis(oxa-zoline) (103) provides the aziridine of styrene in 91% yield and 88% ee. However, this reaction has been found to be irreproducible (76,77) and further reports of aziridination from the Masamune laboratories have not appeared. 

Recently, Gartner and colleagues have reported the [1,2]-Wittig rearrangement of camphor-derived acetal 39 to 40 (equation 21) . 

SCHEME 28. Stereoselective synthesis of camphor-derived tertiary hydroperoxides... 

An oxazoline AT-oxide is a versatile dipole and can react with a variety of dipolarophiles (Scheme 8.134). Langlois group has been very active in this area and has made extensive use of the Ai-oxides of camphor-derived oxazolines for these reactions. The initial adduct can be converted to the anti aldol product after hydrolysis and hydrogenolysis. This subject has been thoroughly reviewed by Langlois, " most recently in 2000. " ... 

Several rules found for the spectra of a series of camphor derivatives (bicyclo[2,2,l]hepta-nones) are worthy of mention (Table 5.5) [548, 549] ... 

Asymmetric hydrogenation of camphor-derived sultamimides (l).2 Hydrogenation of these imides catalyzed by Pd/C proceeds with >90%... 

On the other hand, lithium enolates derived from substituted endocyclic ketones have largely been exploited in the synthesis of steroids since the regioselectivity of their deprotonation can be controlled and high levels of 1,2- and 1,3-stereoselection occur9,418. The control is steric rather than electronic, with the attack directed to the less substituted ji-face of the enolate for conformationally rigid cyclopentanones, whereas stereoelectronic control becomes significant for the more flexible cyclohexanones. Finally, an asymmetric variant of the formation of a-branched ketones by hydration of camphor-derived alkynes followed by sequential alkylation with reactive alkyl halides of the resulting ketones was recently reported (Scheme 87)419. 

As expected, iV-substituted oxaziridines can be obtained by derivatization of NH-oxaziridines. Page et al. reported that a variety of camphor-derived N-substituted oxaziridines 356 can be prepared from NH-oxaziridine 50 (Table 30) <2000JOC4204>. 

Asymmetric Hydrogenation of Camphor-Derived Sul-tamides. The sultamide of CSA can be used as a chiral auxiliary for synthesis of 3-substituted carboxylic acids (eq 20). ... 

In addition, monoterpenes can provide some useful chiral reagents, such as the pinene-based organoborane reagents for chiral reductions that have been reviewed extensively [42]. The use of camphor-derived organic acids such as camphenesulfonic acid can be used for the resolution of racemic bases and is a common practice in industry (see Chapter 8). 

Enantioselective aziridination has also been achieved by use of an enantiopure ligand [70]. Reaction of a variety of N-enoyl oxazohdinones with N-aminophthalimide and lead tetraacetate in the presence of camphor-derived chiral ligands provided the N-phthahmidoaziridines in good to high enantiomeric excess (Scheme 13.49). The oxazohdinone moiety of the substrate played an indispensable role in this reaction. The use of aryl acrylates led either to low stereoselectivity or low chemical yield. Coordination of the hgand-mediated Lewis acid to the bidentate acyl oxazohdinone might account for these results. 

One can oxidize N-sulfonyl imines to the corresponding oxaziridines using oxidants such as a peracid or oxone [5 b, 93,94], Thus, Davis and coworkers have developed a biphasic procedure for converting imine 278 to frans-oxaziridine 279, in high yield [5b] [Eq. (65)]. Similarly, camphor-derived N-sulfonyl imines 277 and 268 can be oxidized to the endo oxaziridines 280 and 281, respectively [92,93] [Eq. (66), (67)]. Davis and others have now demonstrated the exceptional utility of oxaziridines as oxidants in organic synthesis and, in particular, the value of camphor-derived reagents, such as 280 and 281, in asymmetric synthesis [94,95],... 

Based on the elegant work from the group of Studer on redox activation of a,p-unsaturated aldehydes/ the You group realized enantioselective NHC-catalyzed Michael addition reactions to a,p-unsaturated aldehydes by redox oxidation. With 10 mol% of camphor-derived triazolium salt, developed by the authors group, the reactions of various dicarbonyl compounds... 

With the aim of increasing secondary-amine-catalyst turnover, Ogilive and coworkers disclosed the novel class of camphor-derived five-membered cyclic hydrazines 5 to enhance their nucleophilicity by means of the a-heteroatom effect [7]. With the use of this catalyst, aqueous Diels-Alder reactions proceeded efficiently... 

Three-component condensation of silicylaldehyde and two different CH acids to give 2-amino-4//-chromenes, catalysed by base-functionalized ionic liquids, has been investigated experimentally and theoretically. Mechanisms of formation and reaction of camphor-derived amino ketones have been discussed. ... 

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