Camphoric esters

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). 

Table 3.5. Stereoselective alkylation of camphor ester enolates (Scheme 3.14).

Scheme 3.15. Controlled stereoselective enolate formation and asymmetric alkylation of a second generation camphor ester enolate chiral auxiliary [75].

Ma.nufa.cture. The preparation of sulfuryl chloride is carried out by feeding dry sulfur dioxide and chlorine into a water-cooled glass-lined steel vessel containing a catalyst, eg, activated charcoal. Alternatively, chlorine is passed into Hquefted sulfur dioxide at ca 0°C in the presence of a dissolved catalyst, eg, camphor, a terpene hydrocarbon, an ether, or an ester. The sulfuryl chloride is purified by distillation the commercial product is typically 99 wt % pure, as measured by ASTM distillation method D850. 

The doyen of the ester polymers is cellulose nitrate. Camphor-modified cellulose nitrate has been known for over 120 years and still retains its use in a few specialised applications. 

Solids. —It may Idc a hydrocM bon (c .g., paraffin wa, naphthalene) highei alcohol eg., cetyl alcohol) aldehyde e.g., z5-hydroxybenzaldehyde) ketone and qiiinonc e.g., benzo-phenone, camphor) acid (higher fatty, e.g., palmitic acid or aromatic acid) ester (of glycerol, phenols or aromatic alcohols) phenol e.g., thymol),... 

In recent years, several modifications of the Darzens condensation have been reported. Similar to the aldol reaction, the majority of the work reported has been directed toward diastereo- and enantioselective processes. In fact, when the aldol reaction is highly stereoselective, or when the aldol product can be isolated, useful quantities of the required glycidic ester can be obtained. Recent reports have demonstrated that diastereomeric enolate components can provide stereoselectivity in the reaction examples include the camphor-derived substrate 26, in situ generated a-bromo-A -... 

Rabak detected d-camphor, ciuwjl, piueiie, ihev oce. and horneol io tbe oil, as well as Icaces of free Coi niic acid, and loimic j.od acclic acids in the form ot esters. 

Ethyl Cinnamate.—The cinnamic ester of ethyl alcohol is a natural constituent of a few essential oils, including camphor oil and storax. It is formed synthetically by condensing cinnamic acid and ethyl alcohol by dry hydrochloric acid gas. It has a soft and sweet odour, and is particularly suitable for blending in soap perfumes. It is an oil at ordinary temperatures, melting at 12°, and boiling at 271°. Its specific gravity is 1 0546, and its refractive index 1 5590. 

Esters of bomeol are obtained by the action of dry oxalic acid on turpentine under suitable conditions. From these, borneol is obtained by saponification and is oxidised to camphor. Some other acids produce a similar result, as, for example, salicylic and chlorobenzoic acids. 

The action of magnesium on pinene hydrochloride gives rise to bomyl esters, and camphor can be obtained from these in the usual manner. 

Sulfinic esters, aromatic, by oxidation of disulfides in alcohols, 46, 64 Sulfonation ot d,l camphor to d,l-10-camphorsulfomc acid, 45,12 Sulfoxides, table of examples of preparation from sulfides with sodium metapenodate, 46,79 Sulfur dioxide, reaction with styrene phosphorus pentachlonde to give styrylphosphomc diclilonde, 46,... 

There has been some investigation of auxiliary-controlled cycloadditions of azir-ines. Thus, camphor-derived azirine esters undergo cycloaddition with dienes, with poor diastereoselectivity [70]. The same azirines were also observed to react unselectively with phenylmagnesium bromide. Better selectivities were obtained when Lewis acids were used in the corresponding cycloaddition reactions of 8-phe-nylmenthyl esters of azirine 2-carboxylates (Scheme 4.48) [71]. The same report also describes the use of asymmetric Lewis acids in similar cycloadditions, but mediocre ees were observed. 

Addition of the imine of camphor and glycine, as the Michael donor, to a,/i-unsaturated esters yields, after removal of the auxiliary, anP -(22 )-3-substituted glutamates208. 

Optically active bicyclo[2.2,2]octanes can be obtained via diastercoselective MIMIRC reaction of lithium dienolates and a,/ -unsaturated esters of various chiral alcohols. Good yields (70-90%), high endo selectivities (> 95%) and diastereomeric ratios that depend on the auxiliary alcohol are found in these additions. The highest diastereomeric ratio reached was 18 82 using a camphor derived sulfonamide. The diastereomeric ratio could be improved (up to 9 91) by titanium(IV) chloride catalyzed addition of the corresponding silylenolates with the chiral a,/J-unsaturated esters358. 

Very low asymmetric induction (e.e. 0.3-2.5%) was noted when unsymmetrical sulphides were electrochemically oxidized on an anode modified by treatment with (—)camphoric anhydride or (S)-phenylalanine methyl ester . Much better results were obtained with the poly(L-valine) coated platinum electrodes . For example, f-butyl phenyl sulphide was converted to the corresponding sulphoxide with e.e. as high as 93%, when electrode coated with polypyrrole and poly(L-valine) was used. 

Figure 8.43 Separation of enantiomers using complexation chromatography. A, Separation of alkyloxiranes on a 42 m x 0.2S mm I.O. open tubular column coated with 0.06 M Mn(II) bis-3-(pentafluoro-propionyl)-IR-camphorate in OV-ioi at 40 C. B, Separation of D,L-amino acids by reversed-phase liquid chromatography using a mobile phase containing 0.005 M L-histidine methyl ester and 0.0025 M copper sulfate in an ammonium acetate buffer at pH 5.5. A stepwise gradient using increasing amounts of acetonitrile was used for this separation.

Cellulose nitrate (Celluloid) 1850 Moulding material, paints, glues, coatings, photographic films, varnishes Camphor, phthalate esters High flammability and degradability, with production of nitrogen dioxide... 

However, most asymmetric 1,3-dipolar cycloaddition reactions of nitrile oxides with alkenes are carried out without Lewis acids as catalysts using either chiral alkenes or chiral auxiliary compounds (with achiral alkenes). Diverse chiral alkenes are in use, such as camphor-derived chiral N-acryloylhydrazide (195), C2-symmetric l,3-diacryloyl-2,2-dimethyl-4,5-diphenylimidazolidine, chiral 3-acryloyl-2,2-dimethyl-4-phenyloxazolidine (196, 197), sugar-based ethenyl ethers (198), acrylic esters (199, 200), C-bonded vinyl-substituted sugar (201), chirally modified vinylboronic ester derived from D-( + )-mannitol (202), (l/ )-menthyl vinyl ether (203), chiral derivatives of vinylacetic acid (204), ( )-l-ethoxy-3-fluoroalkyl-3-hydroxy-4-(4-methylphenylsulfinyl)but-1 -enes (205), enantiopure Y-oxygenated-a,P-unsaturated phenyl sulfones (206), chiral (a-oxyallyl)silanes (207), and (S )-but-3-ene-1,2-diol derivatives (208). As a chiral auxiliary, diisopropyl (i ,i )-tartrate (209, 210) has been very popular. 

Davis et al.111 developed another method for reagent-controlled asymmetric oxidation of enolates to a-hydroxy carbonyl compounds using (+)-camphor-sulfonyl oxaziridine (147) as the oxidant. This method afforded synthetically useful ee (60-95%) for most carbonyl compounds such as acyclic keto esters, amides, and a-oxo ester enolates (Table 4-20). 

It is also possible to carry out a substrate-controlled reaction with aldehydes in an asymmetric way by starting with an acetylene bearing an optically active ester group, as shown in Eq. 9.8 [22]. The titanium—acetylene complexes derived from silyl propiolates having a camphor-derived auxiliary react with aldehydes with excellent diastereoselectivity. The reaction thus offers a convenient entry to optically active Baylis—Hillman-type allyl alcohols bearing a substituent (3 to the acrylate group, which have hitherto proved difficult to prepare by the Baylis—Hillman reaction itself. 

Asymmetric cyclopropanol formation has been achieved with olefmic acylsulfonamides, which act like olefmic esters. Thus, their reaction with 1 provides a method for synthesizing cyclopropanols in an optically active form. As represented by Eq. 9.41, alkylation of Oppolzer s camphor sultam and reaction of the resulting unsaturated acylsulfonamides with 1 provides optically active bicyclic cyclopropanols having exclusively the structure shown in the equation [76],... 

Tolman and co-workers (67) investigated a series of pyrazolyl-derived ligands for this reaction. Initial investigations centered on the use of tris(pyrazolyl) phosphine oxide (95) as a ligand with chirality derived from camphor. Diastereoselectivities with ethyl diazoacetate are poor, slightly favoring the cis isomer, and enantioselectivities are modest, Eq. 50. The BHT esters greatly increase the diastereoselectivity of this process (96 4) at the expense of enantioselectivity (10% ee for trans isomer). 

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