Steroids carbonyl compounds

Easic Principles Practical Photochemistry General Considerations Carbonyl Compounds a-Cleavage Carbonyl Compounds Hydrogren Abstraction Steroids Carbonyl Compounds Cycloaddition Enone and Dienone Rearrangements Alkenes Isomerisation and Rearrangement Alkenes Cycloaddition Alkenes Photo-Cxidation Terpenoids Aromatic Compounds Isomerisation and Cycloaddition Practical Photochemistry Scale-up Aromatic Compounds Substitution and Cydisation Alkaloids Photoinitiated Free-radical Chain Reactions. 

The following acid-catalyzed cyclizations leading to steroid hormone precursors exemplify some important facts an acetylenic bond is less nucleophilic than an olelinic bond acetylenic bonds tend to form cyclopentane rather than cyclohexane derivatives, if there is a choice in proton-catalyzed olefin cyclizations the thermodynamically most stable Irons connection of cyclohexane rings is obtained selectively electroneutral nucleophilic agents such as ethylene carbonate can be used to terminate the cationic cyclization process forming stable enol derivatives which can be hydrolyzed to carbonyl compounds without this nucleophile and with trifluoroacetic acid the corresponding enol ester may be obtained (M.B. Gravestock, 1978, A,B P.E. Peterson, 1969). 

Diene carboxylates can be prepared by the reaction of alkenyl halides with acrylates[34]. For example, pellitorine (30) is prepared by the reaction of I-heptenyl iodide (29) with an acrylate[35]. Enol triflates are reactive pseudo-halides derived from carbonyl compounds, and are utilized extensively for novel transformations. The 3,5-dien-3-ol triflate 31 derived from a 4,5-unsaturated 3-keto steroid is converted into the triene 32 by the reaction of methyl acrylate[36]. 

Methyl group (Section 2 7) The group —CH3 Mevalonic acid (Section 26 10) An intermediate in the biosyn thesis of steroids from acetyl coenzyme A Micelle (Section 19 5) A sphencal aggregate of species such as carboxylate salts of fatty acids that contain a lipophilic end and a hydrophilic end Micelles containing 50-100 car boxylate salts of fatty acids are soaps Michael addition (Sections 18 13 and 21 9) The conjugate ad dition of a carbanion (usually an enolate) to an a 3 unsatu rated carbonyl compound... 

With certain carbonyl compounds, however, such as 3-keto steroids, the isotopic composition is poor due to the rapid exchange of the activated a-hydrogens in the substrate prior to reduction. The corresponding alcohols, in their thermodynamically more stable configuration, are usually found as... 

The oxidation of a hydroxyl group by an aluminum alkoxide-catalyzed hydrogen exchange with a receptor carbonyl compound is known as the Oppenauer oxidation. For oxidation of steroidal alcohols the reaction is generally... 

Dimethyl sulfoxide reacts with trifluoroacetic anhydride at low tempera ture to give a complex that is an efficient reagent for the oxidation of alcohols to carbonyl compounds [40 41] This reagent can be used to oxidize primary and secondary aliphatic alcohols, cycloalkyl alcohols, and allylic, homoallylic, ben-zylic, acetylenic, and steroidal alcohols (equation 19)... 

The required nitrite esters 1 can easily be obtained by reaction of an appropriate alcohol with nitrosyl chloride (NOCl). The 3-nitroso alcohols 2 formed by the Barton reaction are useful intermediates for further synthetic transformations, and might for example be converted into carbonyl compounds or amines. The most important application for the Barton reaction is its use for the transformation of a non-activated C-H group into a functional group. This has for example been applied for the functionalisation of the non-activated methyl groups C-18 and C-19 in the synthesis of certain steroids. ... 

The oxidation of alcohols to carbonyl compounds has been studied by several authors and a variety of methods have been used. Papers concerned vith such oxidations are illustrated (Scheme 3.26). Good results have been obtained using pyridinium chlor-ochromate (PCC) adsorbed onto silica gel for the selective oxidation of unsaturated substrates e.g. terpene [135] and furanyl derivatives [136]. Steroidal homoallylic alcohols can be converted to the corresponding 4-ene-3,6-diones using tetrapropylammo-nium per-ruthenate (TPAP) in catalytic amounts [137]. In this case, the oxidising agent is N-methyl morpholine N-oxide (NMO). 

Nitrophenyl)ethylene glycol was used to protect simple aldehydes and ketones, as well as some steroids. Acetals were prepared under acid catalysis, leading, in the case of chiral carbonyl compounds to diaste-reoisomers. The photochemical removal of the protecting group was in several instances complicated by the instability of some carbonyl derivatives to irradiation at 350 nm otherwise, yields were in the range of 83-90% (see Scheme 19). 

Nucleophilic Addition to Carbonyl Compounds and -Unsaturated Carbonyl Compounds.—Although the reactions of 17-oxo-steroids with various carbanion reagents are reported to have varying success/ the use of alcohols or DMF as solvents appears to facilitate the Wittig-Horner reaction/ For example, the ketone (97) was converted with (Et0)2P0CHC02Et into the E-ethyl ester (98) in... 

The full account of the use of sulphenylation-dehydrosulphenylation for the introduction of a -unsaturation into carbonyl compounds includes some steroidal examples. The similar selenylation-dehydroselenylation of 17-oxo-steroids resulted in the formation of the unsaturated lactones (118) owing to Baeyer-Villiger oxidation during the H2O2 oxidation of the a-phenyl selenyl intermediate (see also ref. 210). 

Cardenolldes appear to be metabolized by a variety of species, possibly as a mechanism for converting these steroids into compounds that can be efficiently sequestered. The milkweed bug, Oncopeltus fasclatus, metabolizes (hydroxylates ) the nonpolar cardenollde dlgltoxln to more polar compounds that are subsequently sequestered In the dorsolateral space fluid (17. 18). Larvae of another cardenolide-adapted Insect, the monarch butterfly, Danaus plexlppus. also convert these steroids Into compounds that are readily sequestered. For example, uscharldln, which contains a carbonyl group at C-3 ( ) of the... 

Enol ethers can be regiospecifically fluorinated to form a-fluoro carbonyl compounds. In this way it is possible to synthesize fluorinated oxo steroids as the carbonyl groups not activated by the trimethylsilyl (or acetyl) enol ethers are not fluorinated.54... 

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