Camphor ketal

Camphor ketal 65, which can be conveniently prepared by the reaction of myo-inositol with D-camphor dimethyl ketal regioselectively (Scheme 4-4),31 47 showed identical reactivity... 

Bruzik and Tsai applied the protection strategy using the TIPS group to the synthesis of various optically active precursors for inositol phosphates and inositol phospholipids from 1,2-camphor ketal 65 of myo-inositol. ... 

The same camphor ketal (23) was also used in yet another synthesis of... 

Camphor dimethyl ketal, TMSOTf, DMSO, 90°, 3 h, 25% yield. ... 

The C2-symmetric epoxide 23 (Scheme 7) reacts smoothly with carbon nucleophiles. For example, treatment of 23 with lithium dimethylcuprate proceeds with inversion of configuration, resulting in the formation of alcohol 28. An important consequence of the C2 symmetry of 23 is that the attack of the organometallic reagent upon either one of the two epoxide carbons produces the same product. After simultaneous hydrogenolysis of the two benzyl ethers in 28, protection of the 1,2-diol as an acetonide ring can be easily achieved by the use of 2,2-dimethoxypropane and camphor-sulfonic acid (CSA). It is necessary to briefly expose the crude product from the latter reaction to methanol and CSA so that the mixed acyclic ketal can be cleaved (see 29—>30). Oxidation of alcohol 30 with pyridinium chlorochromate (PCC) provides alde-... 

Camphor- 10-sulfonic acid, 62 Unsaturated acetals or ketals Nickel boride, 197 (2R,4R)-Pentanediol, 237 Acetylenic carbonyl compounds a,p-Unsaturated acetylenic carbonyl compounds... 

At an early stage Kitagawa and co-workers followed a path which, unfortunately, did not reach the goal (57). Starting from d-camphor, building block 43 (Scheme 10) was reached via various steps (58). Resolution of diastereomeric ketals of cyclopropanated 3-methylcyclohexanone likewise yielded the chiral... 

The importance of the ethylene ketal described above with respect to stereocontrol of the de-Mayo reaction is emphasized by later published works of two other teams. Fetizon and co-workers obviously followed a similar concept and carried out photocycloaddition reactions with 96a in model studies (Scheme 23) (Si). As can be seen from retroaldol product 98, exclusive a attack of the cyclohexene has taken place. Thus, the relative stereochemistry of the BC ring connection is opposite to that of taxane. Totally comparable results were obtained by Berkowitz et al. in the course of cycloaddition reactions of cyclopentene, cyclohexene, or those of a cyclohexenone ketal to the camphor derivative 96b (.84). 

Determination of the degree and indeed the sense of enantioselection in these reactions is now easily achieved using complexation capillary gas chromatography20. Several chiral liquid phases based on metallic chelates of (1 / )-8-(ethylidene)-3-(heptafluorobutanoyl)camphorate 4 have been developed20 that serve admirably to separate the enantiomers of a wide variety of volatile epoxides, ketals and acetals. 

As a sequel to the elegant and highly efficient synthesis of camphor by an intramolecular cyclization. Money et have successfully applied this method to the synthesis of the naturally-occurring sesquiterpenoids campherenone (110) and campherenol (111) whose structures and absolute stereochemistries have recently been deduced.In this sequence, dihydrocarvone (112) was readily converted into the keto-ketal (113) from which the homologated chloro-ketone (114) was obtained. Treatment of the corresponding enol acetate (115) with boron trifluoride in wet methylene chloride afforded the two bicyclic chloro-ketones (116) and (117) in 55-60% yield. Conversion of the corresponding iodo-ketals... 

DL-Camphor has been resolved by vapor-phase chromatography of the dia-stereolsomerlc ketals prepared with this readily available (by fermentation) diol. ... 

Naturally occurring ketones and their readily prepared derivatives have also been used as chiral auxiliaries. Menthone ketals have been the subject of some study [373, 374], For example, enolates of compound 1.106, obtained from 8-phenylmenthone, are alkylated with a good stereoselectivity [375]. Cleavage of the chiral auxiliary is accomplished by hydrolysis. Enolates of tert-butylglycine camphor imine 1.107 are alkylated [154, 159] or suffer Michael additions [376] with a high stereoselectivity, and the auxiliary is cleaved by treatment of the prod-... 

Ketalization of myo-inositol (1), which is also a symmetrical substance, was carried out with D-camphor dimethyl ketal 179 producing several products, from which after partial hydrolysis of the trans-ketal a diastereomeric mixture of four 1,2-cis-ketals 65a, b, c, and d were obtained (Scheme 4-4).31 When a mixture of the initially formed ketalization products was exposed to acidic conditions in a solvent system of CHCI3, MeOH, and H2O, the major monoketal 65a was obtained preferentially, resulting from the precipitation after decomposition of the trans-ketals and equilibration. The latter procedure provides a practical method for the preparation of a chiral 1,2-protected myo-inositol which can be transformed into various optically active inositol derivatives.1 7 3... 

Camphor sulfonic acid quinoline Enolethers from ketals... 

Curran identified Oppolzer s camphor sultam (cf. 81) [77] as a superb chiral auxiliary for the asymmetric [l,3]-dipolar cycloadditions of nitrile oxides (Scheme 18.17) [78-80]. The resulting cycloadducts were generally obtained with high diastereofacial selectivity (dr 90 10). It was proposed that the observed facial differentiation was the result of attack by the nitrile oxide from the top face of conformer 84. This was suggested to be favored on the basis of electronic and steric effects, a proposition that finds support in an X-ray structural analysis of 81 [78, 80]. Cycloaddition of 81 with the nitrile oxide generated in situ from 80 led to isoxazoline 82 in 89 % yield (dr= 92 8). This product constituted a key intermediate in Curran s total synthesis of 83, a bicyclic ketal isolated from ambrosia beetles [80]. 

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