Lactones alcohols, cyclic

Molybdenum-peroxo compounds have been shown to achieve a variety of selective oxidations they a-hydroxylate enolizable ketones, presumably via epoxidation of the enolate (equation 27) 163 they cause Baeyer-Villiger lactonization of cyclic ketones, probably via the formation of five-membered trioxametallacycles (equation 28) 164 they oxidize alcohols to carbonyl compounds... 

Intramolecular cyclization is a useful method for the preparation of lactones and cyclic ethers [34], The most common examples are iodolactonization and iodoetherification, the former using a carboxylic acid derivative as the nucleophile and the latter relying on a hydroxy group. Thus, butyrolactones are available from Y, -unsaturated carboxylic acid derivatives [1,35,36], while unsaturated alcohols lead to cyclic ethers [37-40], Lactones are also available from a wide variety of nucleophiles such as carbonates [41], orthoesters [42], or carbamates [43,44], which can all be used in place of a carboxylate anion [44,45],... 

Silver carbonate-Celite Lactones from cyclic alcohols... 

There is a wide variety of reactants in this reaction. Suitable unsaturated starting materials or unsaturated compound-forming components are acetylenes, olefins, alcohols, cyclic and non cyclic ethers, epoxides, acetals, esters, saturated aldehydes, lactones and halides. Water, alcohols, ammonia, amines, mercaptans and carboxylic acids, e. g. are used as nucleophilic compounds with mobile hydrogen atoms. 

Lactone A cyclic ester that can form from an internal con densation between an alcohol functional group and a carboxylic acid functional group. 

Further hydrolysis causes the lactone (a cyclic ester) to open to a carboxyl group and an alcohol group (Section 16.10). 

FIGURE 14.25 Catalytic antibodies are designed to specifically bind the transition-state intermediate in a chemical reaction, (a) The intramolecnlar hydrolysis of a hydroxy ester to yield as products a S-lactone and the alcohol phenol. Note the cyclic transition state, (b)... 

The next key step, the second dihydroxylation, was deferred until the lactone 82 had been formed from compound 80 (Scheme 20). This tactic would alleviate some of the steric hindrance around the C3-C4 double bond, and would create a cyclic molecule which was predicted to have a greater diastereofacial bias. The lactone can be made by first protecting the diol 80 as the acetonide 81 (88 % yield), followed by oxidative cleavage of the two PMB groups with DDQ (86% yield).43 Dihydroxylation of 82 with the standard Upjohn conditions17 furnishes, not unexpectedly, a quantitative yield of the triol 84 as a single diastereoisomer. The triol 84 is presumably fashioned from the initially formed triol 83 by a spontaneous translactonization (see Scheme 20), an event which proved to be a substantial piece of luck, as it simultaneously freed the C-8 hydroxyl from the lactone and protected the C-3 hydroxyl in the alcohol oxidation state. 

Reduction of Cyclic Anhydrides to Lactones and Acid Derivatives to Alcohols... 

Additions of silylated ketene acetals to lactones such as valerolactone in the presence of triphenylmethyl perchlorate in combination with either allyltrimethylsilane 82, trimethylsilyl cyanide 18, or triethylsilane 84b, to afford substituted cyclic ethers in high yields have already been discussed in Section 4.8. Aldehydes or ketones such as cyclohexanone condense in a modified Sakurai-cyclization with the silylated homoallylic alcohol 640 in the presence of TMSOTf 20, via 641, to give unsaturated cyclic spiro ethers 642 and HMDSO 7, whereas the 0,0-diethyllactone acetal 643 gives, with 640, the spiroacetal 644 and ethoxytrimethylsilane 13b [176-181]... 

The highly ordered cyclic TS of the D-A reaction permits design of diastereo-or enantioselective reactions. (See Section 2.4 of Part A to review the principles of diastereoselectivity and enantioselectivity.) One way to achieve this is to install a chiral auxiliary.80 The cycloaddition proceeds to give two diastereomeric products that can be separated and purified. Because of the lower temperature required and the greater stereoselectivity observed in Lewis acid-catalyzed reactions, the best diastereoselectivity is observed in catalyzed reactions. Several chiral auxiliaries that are capable of high levels of diastereoselectivity have been developed. Chiral esters and amides of acrylic acid are particularly useful because the auxiliary can be recovered by hydrolysis of the purified adduct to give the enantiomerically pure carboxylic acid. Early examples involved acryloyl esters of chiral alcohols, including lactates and mandelates. Esters of the lactone of 2,4-dihydroxy-3,3-dimethylbutanoic acid (pantolactone) have also proven useful. 

Following the results obtained in the intermolecular carbonylation of alkenes in the presence of alcohols, it seemed conceivable that an alkene-bearing alcohol functionality would react in an intramolecular way giving a cyclic ester as the main product. Thus, the carbonylation (also referred to as cyclocarbony-lation as a cyclization occurs simultaneously) of alkenols (or hydroxyalkenes) was investigated for the selective preparation of lactones. 

Upon addition of acid, the alcohol reacts with the carboxylic acid to give a lactone (cyclic ester). This acid-catalyzed reaction is discussed in detail in Chapter 3. The reaction is far more likely to occur by attack of Oil on C13 than by attack of 014 on CIO. 

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