Alcohols conversion give

These methods were not applicable to all acids, and various alternative routes were investigated. The conversion of an acid to its methri ester by diazomethane is a method of choice when other methods are unsatisfactory (6, 30, 61, 65). With appropriate alcohols thiazoleanhydrkies give the esters or diesters in good yield (64), dimethyl 2-phoiyl-4,5-thiazoledicarboxylate (13) has been prepared in this way (Scheme 8) (17). 

Compound A can be resolved to given an enantiomerically pure substance, [a]p = —124°. Oxidation gives the pure ketone B, which is optically active, [aJo — —439°. Heating the alcohol A gives partial conversion (an equilibrium is established) to an isomer with [a]p = +22°. Oxidation of this isomer gives the enantiomer of the ketone B. Heating either enantiomer of the. ketone leads to the racemic mixture. Explain the stereochemical relationships between these compounds. 

Of course, the influence of organic solvents on enzyme enantioselectivity is not limited to proteases but it is a general phenomenon. Quite soon, different research groups described the results obtained with lipases [28]. For instance, the resolution of the mucolytic drug ( )-trans-sobrerol (11) was achieved by transesteriflcation with vinyl acetate catalyzed by the lipase from Pseudomonas cepacia adsorbed on celite in various solvents. As depicted in Scheme 1.3 and Table 1.5, it was found that t-amyl alcohol was the solvent of choice in this medium, the selectivity was so high ( >500) that the reaction stopped spontaneously at 50% conversion giving both +)4rans-sobrerol and (—)-trans-sobrerol monoacetate in 100% optical purity [29]. 

Williams employed complexes of Al, Rh, or Ir in combination with Pseudomonas Jluorescens lipase (PFL) for the DKR of 1-phenylethanol. The best results were obtained using Rh2(OAc)4 as the catalyst for the racemization, and 60% conversion of the alcohol to give 1-phenylethyl acetate in 98% ee was obtained (Figure 4.6) [19]. At higher conversion, the enantiomeric excess dropped and 76% conversion gave 80% ee. 

This method is especially useful for the conversion of ketones to ketals, since the direct reaction of a ketone with an alcohol often gives poor results. In another method, the substrate is treated with an alkoxysilane ROSiMe3 in the presence of trimethylsilyl trifluoromethanesulfonate. ... 

The following compilation shows the results of a reaction sequence consisting of the conversion of carboxylic acids by A -oxalyldiimidazole (A) or A -oxalyld 1,2,4-triazole) (B) into the corresponding azolides followed by acid-catalyzed reaction with alcohols to give the appropriate esters.tl38]... 

The conversion of 8 to 9 uses PPI13 and I2. The former is a nucleophile, the latter is an electrophile, so they react to give PI13P-L The P is attacked by the alcohol to give an O-P bond, and the I- then displaces PI13PC) from C to give the alkyl iodide. 

Oxidation of 2-(trimethylsilyloxy)furan (301) with iodosobenzene in the presence of boron trifluoride etherate and alcohols or acids results in the formation of 5-substituted 2(5//)-furanones 303. The first step of this conversion gives intermediate 302, which on nucleophilic substitution by alcohols or acids affords the products (89TL3019) (Scheme 75). 

Conjugate addition to 1 proceeded across the open face of the bicyclic system to give an enolate, condensation of which with the enantiomerically-pure aldehyde 8 gave the enone 9. Conjugate reduction of the enone also removed the benzyl ether, to give the alcohol. Conversion of the alcohol to the azide gave 10. Ozonolysis followed by selective reduction then gave 2. 

This method is particularly effective with cyclic substrates, and the combined effects of intramolecular and intermolecular asymmetric induction give up to 76 1 (kf/ks) differentiation between enantiomers of a cyclic allylic alcohol. This kinetic resolution provides a practical method to resolve 4-hydroxy-2-cyclopentenone, a readily available but sensitive compound. Hydrogenation of the racemic compound at 4 atm H2 proceeds with kf/ks =11, and, at 68% conversion, gives the slow-reacting R enantiomer in 98% ee. The alcoholic product is readily convertible to its crystalline, enantiomerically pure fert-butyldimethylsilyl ether, an important building block in the three-component coupling synthesis of prostaglandins (67). 

The carbanion is trapped with iodine to give 42. which makes a further functionali/aiion possible. Conversion of vinylic iodide 42 into a lactone is accomplished by palladium-cataly/ed carbonyla-tion under Stille conditions.13 This process ean be broken down into the following elementary reactions a) Oxidative addition of Pd° to vinylic iodide 42 with formation of 43 b) An insertion reaction of carbon monoxide with creation of the pallada-acyl species 44 c) Reaction of acid-chloride equivalent 44 with the alcohol to give lactone 13. 

Trost used the dihydroxylation methodology extensively in the total synthesis of (+)-parvi-florin (68) [96]. Both bistetrahydrofuran elements were prepared from 8, tn-dienyl alcohol 71. To avoid overoxidation the reaction was stopped before complete conversion, giving triol 72 with 94% ee in 71 % yield. Protection as the acetonide afforded 73 and subsequent hydrogenation furnished saturated alcohol 74. The construction of 75 was accomplished by Julia olefination using derivatives of 73 and 74. Diene 75 was thenregioselectively dihydroxylated at the internal... 

Diastereoselective protonation of arylmethylketenes. Merck chemists1 have described a conversion of (R,S)-2-arylpropionic acids (1) into the optically active forms. Thus 1 is converted into the corresponding arylmethylketene (2). Addition of a chiral alcohol can give optically active a-hydroxy esters 3 (and the acids). Of a... 

Since these products are, therefore, readily available as starting materials we have studied their further use. The diazido compounds 38 are not very stable. They loose readily dinitrogen (usually on crystallization from alcohol) and give the tetrazolyl derivatives 39. Treatment of 39 with acetic anhydride leads in the usual way (cf. the conversion of 3 via 9-11 to 12) to the oxadiazolyl derivative 40. The carbonyl group in this structure can be reduced with sodium borohydride to the methylene group. Careful hydrolysis of this compound (41) with acid, yields the hydrazide 42, while alkaline hydrolysis of both affords the acid 43 [84JHC1881],... 

Nucleophilic substitution of toluene- -sulphonates (tosy-lates) and other sulphonic esters of secondary steroidal alcohols has received much attention, both in studies of reaction mechanisms, and also as a route for the conversion of alcohols into their epimers. One of the most important practical objectives has been the synthesis of 3a-hydroxy-5a-steroids, which include androsterone and a wide variety of metabolites of the steroid hormones, Tosylates of equatorial 3jS-alcohols (15) give 3a-alcohols or their derivatives (16) in acceptable... 

Ionization after an initial reaction that converts one functional group into a leaving group, as in protonation of an alcohol to give an oxonium ion or conversion of a primary amine to a diazonium salt, both of which ionize to the corresponding carbocation ... 

A simple method for the preparation of primary amines from aliphatic halides involves the treatment of the halide with KOCN in alcohol to give the urethane which is hydrolyzed to the amine. In general the yields are high. A novel conversion in which tetrakis(dimethylamino) titanium converts carboxylic acids and their common derivatives in orthoamides and ketene N,N-acetals in good yields is described. ... 

Heinen et al. [35] investigated the oxidation of D-fructose on Pt/C catalyst at 30 °C and pH 7.3. Oxidation of both the C, primary alcohol and the C5 secondary alcohol occurred. The reaction stopped at ca 80 % conversion giving mainly 2-keto-D-gluconic acid (45% selectivity) and D-t/n-eo-hexo-2,5-diulose or 5-ketofructose (27 % selectivity). In the presence of bismuth-promoted catalysts selectivity to the former was slightly increased. This was attributed to the complexation by bismuth of the y9-o-fructofuranose stmcture via the c/s-diol functions. 

We first screened several transition metal conqtlexes which have been shown to have activity in transferring oxygen from hydroperoxides onto organic substrates via peroxometal intermediates. If such an intermediate is capable of coordinating an alcohol moiety, this may produce a potentially active catalyst for alcohol oxidation. The results of the oxidation of the alcohol with t-BuOOH are listed in Table 1. The molybdenum conqjlex effected a conqrlete conversion of the t-BuOOH to t-BuOH (Run 1) at very low efficiency towards the formation of the aldehyde with the alcohol converted primarily to the acid which further reacted with the t-BuOH or the starting alcohol to give the esters. The use of the other complexes, with the exception of the ZrO(OAc)2 (Run 5), led to low conversions and low selectivity to the aldehyde. 

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