Lactones, from ethers

The residue (12 g) which contains the 18-iodo-18,20-ether is dissolved in 200 ml of acetone, 5 g of silver chromate is added Note 3) and after cooling to 0°, 11.8 ml of a solution of 13.3 g of chromium trioxide and 11.5 ml of concentrated sulfuric acid, diluted to 50 ml with water is added during a period of 5 min. After an additional 60 min, a solution of 112 g of sodium acetate in 200 ml of water is added and the mixture diluted with benzene (400 ml), filtered and the benzene layer separated. The aqueous phase is reextracted with benzene, washed with half-saturated sodium chloride solution, dried and evaporated to yield 11.2 g of a crystalline residue. Recrystallization from ether gives 7.2 g (72%) of pure 3/5, 1 la, 20/5-trihydroxy-5a-pregnan-18-oic acid 18,20 lactone 3,11-diacetate mp 216-218°. 

Isolation of Sesquiterpene Lactones. The ether extract was evaporated and dissolved in 952 ethanol. Then an equal volume of 42 aqueous lead acetate was added. After 1 hour the mixture was filtered to remove precipitated chlorophyll and phenolic products and the ethanol removed under vacuum. The aqueous layer was extracted with chloroform giving a dark colored oil from which the sesquiterpenes were isolated by a combination of chromatographic procedures, i.e., LH-20 gel permeation, silica gel using both packed columns and thin layer plates. A variety of solvents were also used to purify the individual sesquiterpene lactones, e.g., benzene-acetone (1 1), ethyl acetate, chloroform-methanol (9 1). On thin layer chromatographic plates, spots were visualized by spraying with 22 aqueous KMn04 solution. 

Scheme 34 Non-anomeric bicyclic lactones from carboxyalkyl ethers...

Intramolecular Addition Formation of Cyclic Enol Ethers and Lactones from Pent-4-yn-1-ols and But-3-yn-1-ols... 

In general, dehydration means loss of water molecules from chemical substances, irrespective of their structure. Even if all cases where water is bonded in hydrate form are excluded, a number of reactions remain which also include formation of nitriles from amides, lactones from hydroxy acids etc. However, the present treatment will concentrate on the heterogeneous catalytic decomposition of alcohols in the vapour phase, which can be either olefin-forming or ether-forming reactions, and on the related dehydration of ethers to olefins. 

B. 3,4-Dihydro-2-methylene-2H-1-ben2opyran. Formation of the exomethylene enol ether with dihydrocoumarin is carried out as in the foregoing procedure except that the reaction solution is cooled with a dry ice-acetone bath before addition of the lactone. From 3.0 g (20 mmol) of dihydrocoumarin (Note 5) is obtained 1.85-1.97 g (63-67%) of the product (Note 12) as a pale yellow oil, after column chromatography on basic alumina (150 g) eluting with 5% diethyl ether in pentane. 

Although this material is sufficiently pure for some applications, it is advisable to purify it further before use. Distillation2 and crystallization have been described. The submitters recommend purification by the distillation procedure given. By direct crystallization of 101 g of crude lactone acid from ether/petroleum ether, the checkers obtained 36.5 g (35%) of material, mp 72-74°C. 

In the presence of suitable catalysts, /3-lactones are formed by the action of ketene on aldehydes and ketones. Many catalysts have been used those preferred for aldehydes include boric acid, triacetyl borate, zinc thiocyanate, and zinc chloride. Ketones require stronger catalysts such as boron ttifluoride etherate. The reactions ate conducted at low temperatures (0-10°) to minimize polymerization of the product. Yields of /6-lactones from formaldehyde and acetaldehyde are 85%. The /3-lactones formed from conjugated olefinic ketones decompose to dienoic acids which isomerize to olefinic S-lactones. ... 

Accordingly, bishydroxylation of the enol ether then gave an 80% yield of hydroxy ketones 37a and 37b. The ratio of these two compounds varied depending upon the reaction conditions, but the desired syn compound 37a always was major product in at least a 3 1 ratio. Succinylation of the mixture of 37a and 37b followed by -elimination of phenylsulfinic acid gave a mixture of diastereomeric lactones from which synthetic 1 could be isolated. 

The natural pyrone yangonin (10) was synthesized by condensation of triacetic acid lactone methyl ether (8) with p-methoxybenzaldehyde (9) in the presence ol magnesium methoxide (prepared from 200 mg. magnesium and 10 ml. CH lOH)7... 

A very carefully thought out test of the reahty of electrostatic stabilisation of a developing oxocarbonium ion was applied by Loudon and Ryono [95] using compounds XXXIV and XXXV. (The oxocarbonium ion is generated by rate-determining proton transfer to the vinyl ether function, rather than by departure of a leaving group.) Neither carboxylate can participate nucleophihcally any lactone from XXXIV would be unconscionably strained. Furthermore, water molecules in XXXIV cannot be accommodated between the carboxylate and the oxocarbonium ion centre the endo face of the system is hydrophobic. 

Kaneko, H. and K. Ijichi The aroma of cigar tobacco. Part 1. Isolation of 2-hydroxy-2,6,6-trimethylcyclohexy-lidene-1-acetic acid lactone (dihydroactinidiolide) from ether extract of cigar leaves Agr. Biol. Chem. Japan 32 (1968) 1337-1340. 

Protection of y-lactones. y-Lactones can be converted in about 90%, yield into protected lactols by reduction with diisobulylaluminum hydride (1, 261 2, 140) followed by reaction with an alcohol in the presence of BFa etherate. Kegeneration of the lactone can be effected in high yield in one step by reaction with 1.1 cquiv. of m-chloroperbenzoic acid in CH2CI2 containing BF3 etherate. This regeneration step gives low yields of 8-lactones from S-lactols. 

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