Lactones acid-catalyzed

Synthesis of (A) started with the combination of 2,4,6-trimethylphenol and allyl bromide to give the or/Ao-allyl dienone. Acid-catalyzed rearrangement and oxidative bydroboration yielded the dienone with a propanol group in porlactone ring were irons in the product as expected (see p. 275). Treatment with aqueous potassium hydroxide gave the epoxy acid, which formed a crystalline salt with (R)-l-(or-naphthyl)ethylamine. This was recrystallized to constant rotation. 

L-Sorhose to 2-KGA Fermentation. In China, a variant of the Reichstein-Grbssner synthesis has been developed on an industrial scale (see Fig. 5). L-Sorbose is oxidized direcdy to 2-ketogulonic acid (2-KGA) (24) in a mixed culture fermentation step (48). Acid-catalyzed lactonization and enolization of 2-KGA produces L-ascorbic acid (1). 

The acid-catalyzed ring opening of the four-memhered ring lactone in... 

Curran s synthesis of ( )-A9(l2)-capnellene [( )-2] is detailed in Schemes 30 and 31. This synthesis commences with the preparation of racemic bicyclic vinyl lactone 147 from ( )-norbomenone [( )-145] by a well-known route.61 Thus, Baeyer-Villiger oxidation of (+)-145 provides unsaturated bicyclic lactone 146, a compound that can be converted to the isomeric fused bicyclic lactone 147 by acid-catalyzed rearrangement. Reaction of 147 with methylmagne-sium bromide/CuBr SMe2 in THF at -20 °C takes the desired course and affords unsaturated carboxylic acid 148 in nearly quantitative yield. Iodolactonization of 148 to 149, followed by base-induced elimination, then provides the methyl-substituted bicyclic vinyl lactone 150 as a single regioisomer in 66% overall yield from 147. 

Substituted allylsilanes are available from the corresponding carboxylic acid esters by treatment with an excess of trimethylsilylmethylmagncsium chloride and cerium(UI) chloride followed by acid catalyzed elimination31. Lactones give rise to 2-([Pg.344]

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. 

A series of N-substituted narceine amides (Section III,D,1) was prepared from 101 under the action of primary amines (100). Acid-catalyzed dehydration transformed these amides to corresponding imides (ene lactams) of the ( )-narceine imide (117) type (100). Similar transformations were performed in the hydrastine series (101). JV-Methylhydrastine (98) when treated with dilute ammonium hydroxide gave hydroxy lactam 127, which was dehydrated to (Z)-fumaridine (113) (5). Sodium borohydride was able to reduce the stilbene double bond in 98 to produce saturated lactone 132 (5). 

It has been shown that Lewis acid catalyzed isomerization of thionolactones provides access to thiolactones. For example, exposure of the substrate 22 to catalytic amounts of BF3 OEt2 led to efficient conversion to the thiolactone 23. Such transformations were also found to give minor amounts of lactone or dithiolactone side products <06TL6067>. Substituted tetrahydrothiophene derivatives have also been obtained from 1,4-dithiane-2,5-diol and 2-nitroethyl acetate derivatives by a base induced sequence featuring a Michael addition and a Henry reaction <06TL8087>. 

On route to the Erythrina alkaloid 3-dimethoxyerythratidinone, Wang and Padwa encountered the interesting acid catalyzed rearrangement of lactam 151 to the tetracyclic hydroxyindole 153 via the lactone 152 <060L601>. 

Hoye demonstrated that the carbonyl group that lies on the C2-symmetric axis in keto diacid 119 can be reduced to alcohol 120. When followed by acid-catalyzed lactonization of the hydroxyl group with either a C-l or C-9 carboxyl group, monolactone 121 or ent-121 can be produced, thus realizing the desymmetrization of substrate 119 (Scheme 8-45). 

The acid catalyzed conversion of gamma-hydroxy-butyric acid into its lactone was studied In 0.2 N HC1 solution at 25 C. The initial concentration of the acid was 18.23 in arbitrary units. The lactone concentration was... 

Reaction of D-glucono-1,4-lactone with 2,2-dimethoxypropane-tin(II) chloride yields the 5,6-0-isopropylidene derivative 13, which on periodate oxidation afforded 2,3-0-isopropylidene-D-glyceraldehyde (21). However, the acid-catalyzed isopropylidenation of D-glucono-1,5-lactone with 2,2-dimethoxypropane afforded methyl 3,4 5,6-di-0-isopropylidene-D-gluco-nate (14) as the main product (22). Reduction of the ester function gave... 

The acid-catalyzed acetalation of aldonolactones with alkyl acetals of aldehydes or ketones takes place, in some instances, with esterification of the lactone group to give acetal derivatives of alkyl aldonates (11,22). 

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. 

M. J. Kaufman, Rate and Equihbrium Constants for Acid-Catalyzed Lactone Hydrolysis of HMG-CoA Reductase Inhibitors , Int. J. Pharm. 1990, 66, 97-106. 

We were interested in applications of the high level of stereocontrol associated with the asymmetric Birch reduction-alkylation to problems in acyclic and heterocyclic synthesis. The pivotal disconnection of the six-membered ring is accomplished by utilization of the Baeyer-Villiger oxidation (Scheme 7). Treatment of cyclohexanones 25a and 25b with MCPBA gave caprolactone amides 26a and 26b with complete regiocon-trol. Acid-catalyzed transacylation gave the butyrolactone carboxylic acid 27 from 26a and the bis-lactone 28 from 26b cyclohexanones 31a and 31b afforded the diastereomeric lactones 29 and 30. ... 

Lewis acid-catalyzed decomposition of iodonium ylide 49 in the presence of alkenes results in the formation of y-lactones 50 (87IZV2873) (Eq. 20). 

L-Aldono-1,4-lactones can be prepared from o-aldose perpivaloates and perace-tates (compounds of type 17) [28]. The method implies formation of aldoximes (18), followed by mesylation (Scheme 7). The resulting 5-0-mesyl glyconitrile derivatives (19) are then submitted to acid-catalyzed hydrolysis giving the corresponding 1,4-lactones 20a-c. 

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