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Reakcje rozszczepiania laktonów : zastosowanie w syntezie organicznej

Skiera I., Paryzek Z.

Wiadomości Chemiczne

2004

[Z] 58, 11-12

845--879

Lactones, being derivatives of hydroxy carboxylic acids, represent a special group of intramolecular esters. A large number of biologically important natural products are derivatives of chiral y- and 8-lactones. In addition, these commonly encountered compounds, due to their high reactivity, are valuable synthetic intermediates. Lactones are particularly susceptible to nucleophilic attack. As a consequence, the cleavage of the lactone ring is a commonly used process in laboratory synthesis of organic compounds and in industry. Cleavage of lactones may be effected under variety of reaction conditions including reagents, catalysts, solvents and temperature. The chemoselectivity observed in these reactions allows selective reactions of multifunctional compounds, very often of rather complicated structure. The enhanced reactivity of lactones toward nucleophiles makes hydrolysis their most investigated reaction. The ring cleavage occurs under basic (alkali metal hydroxides or alkoxides, tertiary amines) or acidic (Bronsted or Lewis acids) conditions. The effective cleavage of the lactone ring occurs also in reactions with nitrogen nucleophiles, which include ammonia, primary and secondary amines and hydrazine derivatives, as commonly used reagents. Sulphur and selenium derivatives are prepared in reactions of lactones with S- and Se-nucleophiles. The effective nucleophilic reducing agents include metal hydrides, of which lithium aluminium hydride is the most frequently used reagent. Other reducing agents like sodium borohydride and other complex boron hydrides have also been reported. Reductive cleavage of lactones under catalytic hydrogenation conditions and with the aid of complex reducing systems are discussed. The metaloorganic reagents effectively cleave lactones, while a new carbon-carbon bonds are formed. Since the literature concerning transformations of lactones is enormous, in this review the selected examples are included to demonstrate usefulness of lactone cleavage reactions for diverse synthetic purposes.

Unusual Ozonolysis of Cholesteryl and Androst-5-en-3beta-yl Acetates in the Presence of Primary Amines. Formation of A-nor-3(5--6alfa)abeo-6beta(H)-5-oxo-steroids, Confirmed by X-ray Analysis

Paryzek Z., Koenig H., Skiera I., Rychlewska U.

Polish Journal of Chemistry

2002

Vol. 76 / nr 7

921-930

The reaction of cholesteryl acetate with ozone in the presence of amines has been studied. Besides the expected cleavage products, B-seco-ketoaldehyde and its aldol condensation product, 5-hydroxy-6-formyl-B-nor-5_-cholestane derivative, the abnormal product, 3_-acetoxy-A-nor-3(5_6_)abeo-6_(H)-cholestan-5-one is formed as a result of a new, anomalous cleavage of the primary ozonide. The reaction conditions and isolation procedure were optimized for achieving good yield of the abeo-compound. The X-ray crystal structure analysis confirmed the formation of the unusual steroidal skeleton. It appears to be the first crystallographic analysis of the transformed steroid with A-nor-3(5_6_)abeo skeleton. No product resulting from the amine nucleophilic participation in the cleavage of ozonides was observed.