Camphor-based Alcohols

Naturally occurring compounds containing the bicyclo[2.2.1]heptane skeleton Reviews  

Oppolzer, M. Kurth, D. Reichlin, C. Chapuis, M. Mohnhaupt, F. Moffat, Helv. Chim. Acta 64 (1981) 2802. 

Helmchen, A. Selim, D. Dorsch, I. Taufer, Tetrahedron Lett. 24 (1983) 3213. 

---

Several methods for asymmetric C —C bond formation have been developed based on the 1,4-addition of chiral nonracemic azaenolates derived from optically active imines or enamines. These methods are closely related to the Enders and Schollkopf procedures. A notable advantage of all these methods is the ready removal of the auxiliary group. Two types of auxiliaries were generally used to prepare the Michael donor chiral ketones, such as camphor or 2-hydroxy-3-pinanone chiral amines, in particular 1-phenylethanamine, and amino alcohol and amino acid derivatives. 

A new chiral auxiliary based on a camphor-derived 8-lactol has been developed for the stereoselective alkylation of glycine enolate in order to give enantiomerically pure a-amino acid derivatives. As a key step for the synthesis of this useful auxiliary has served the rc-selective hydroformylation of a homoallylic alcohol employing the rhodium(I)/XANTPHOS catalyst (Scheme 11) [56]. 

In 1965, Denney et al. (98) reported the reaction of a number of alkenes with ferf-butyl hydroperoxide (TBHP) and cupric salts of chiral acids. The use of ethyl camphorate copper complex 144 in the allylic oxidation of cyclopentene provides, upon reduction of the camphorate ester, the allylic alcohol in low yield and low selectivity, Eq. 82. The initial publication only provided the observed rotation of cyclopentenol, but comparison to subsequent literature values (99) reveals that this reaction proceeds in 12% ee and 43% yield (based on the metal complex). 

A fruitful approach to obtain asymmetric polymer synthesis was proposed by Overberger (126) who suggested that propagation could be influenced and optically active polymers could be synthesized by using optically active gegen-ions. Schmidt and Schuerch (127) followed up this suggestion and used boron trifluoride in conjunction with asymmetric Lewis bases (1-a-methyl benzyl alcohol, tosyl L-valine, camphor) to polymerize certain cyclic olefins. However, in spite of careful work and various modifications in reaction conditions, no optical activity was obtained in the polymers in this first attempt to test this ingenious hypothesis. 

In works made under direction of N.M. Emanuel they showed that catalytic system [Cu2+... A. .. 02] where A" - the anion form of substrate (anion form of substrate was formed at the expense of its deprotonation under the action of bases introduced into the system) is extremely effective in reactions of oxidation of fluorinated alcohols with general formula H(CF2CF2)nCH2OH (where n=l-6) [2], camphor [3] and diacetone-L-sorbose [4] with... 

Form Supplied in red solid prepared from optically pure d-camphor oxime in a five-step sequence (eq 1) reduction with sodium in n-amyl alcohol followed by fractional recrystallization of the resulting hydrochloride salts of bornylamines gives the endo-isomer in enantiomerically pure form treatment with phosgene and direct condensation of the isocyanate with (ethoxycarbonyl)hydrazine gives a compound which cyclizes upon treatment with base subsequent nitrogen dioxide oxidation furnishes (-)-en[Pg.145]

In 1951 Bothner-By first attempted asymmetric reductions based on the conversion of lithium aluminum hydride (LAH) into a chiral alkoxy derivative by reaction with (+)-camphor. Since this pioneering work, the use of chirally modified LAH reagents has been the focus of much attention. In 1979, the first virtually complete enantiofacial recognition of prochiral carbonyl compounds was accomplished by using LAH modified with optically pure 2,2 -dihydroxy-1,1 -binaphthyl and a simple alcohol (BINAL-H). Asymmetric reduction with chiral 2,5-dimethylborolane also gave alcohols in high optical yields." Recently, excellent results have been obtained using a chirally modified sodium borohydride... 

Similarly, if the racemic mixture is composed of basic drugs, use is made of camphor-10-sulfonic acid, a natural product obtainable as an optically pure enantiomer. An example of the type of reactions involved is shown in Figure 4.13, where a pair of enantiomeric alcohols is resolved by reaction with phthalic anhydride and an optically pure base to form a pair of diastereoisomeric salts. Reactions of this type can be tedious to perform and, with the advent of HPLC with chiral stationary phases, are gradually being replaced. 

Terpenes are are a class of compounds whose chemical structures are based on a number of isoprene units , derived from the hydrocarbon CH2=C(CH3)-CH=CH2 they may themselves be hydrocarbons, but may also contain alcohol (OH), aldehyde/ketone (CO) and carboxylic acid (COOH) groups. Monoterpenes are Cm compounds derived from two isoprene units, sesquiterpenes (Cu) are derived from three isoprene units, diterpenes (C20) from four and tritepenes (C30) from six. Terpenes are widespread in plants, where they are largely responsible for the odor, and they are the major constituents of plant-derived essential oUs . Among the best known terpenes are 3-pinene (turpentine), camphor, menthol and citroneUal (aU monoterpenes) and farnesol (a sesquiterpene that is a constituent of the essential oils of many plants). Certain terpenes have important biological roles vitamin A, for example, is a diterpene, and steroid hormones have a structure related to triterpenes (and are biosynthesized by a similar route). 

This cream and ointment contain menthol in an alcohol base gel, combinations of methyl salicylate, and menthol in cream and ointment bases, as well as a combination of methyl salicylate, menthol, and camphor in a nongreasy cream base all are suitable for topical application. The varieties include the ointment (methyl salicylate, 18.3% ... 

---