Steroid enols

Acyl hypofluorites react readily with ends, enol acetates, vinyl ethers, and enolates [39, 40, 41] (Table 2, entries 1-7) Steroidal enol acetates are also fluorinated smoothly [39] (equations 17-19)... 

The photorearrangement of enol esters is strictly intramolecular. Upon irradiation of two different steroidal enol acetates, one of them possessing a trideuterated acetyl group, the original isotope labels were fully retained in the products.105... 

F-Teda BF4 (6) is very effective for the fluorination of a wide variety of organic substrates steroidal enol acetates (Table 7)92 and silyl enol ethers, certain carbanions, mildly activated aromatic compounds, and sulfides bearing oc-H atoms.73,75,76,77,84,88 90 The products are obtained with good yields and regioselectivity under very mild reaction conditions (Table 8). 

EpoxyacetateB have also keen prepared from steroid end aoetatc by Huechmann and Wendler,7 Soloway and co-workers,1801 and Leeds and eo-workers.888 Moffett and Stomp 187 have found, with certain unsatorated steroid enol acetates, that where a choice reaction sites exists perbenzoic add attacks a simple olefinie double bond preferentially. At higher temperatures and with excess l peroxy add, however, there ooouzs epoxidation of the enol acetal... 

Although Hurd and Edwards 43 have reported the isolation of n epoxy ether from perbenzoie acid oxidation of 2,3-dihydropyi-in>. m< other instance of this Bort is known. In fact it is known114 that treatment of 20-oxo steroid enol ethers with perbenzoie acid givci an unisolable epoxy ether, winch readily undergoes cleavage to vivr 17-oxo steroids as Bhown in Eq. (216). 

Steroidal enol acetates were similarly epoxidized. This method has undoubted advantages over the tradional epoxidation by peracids. Metal-catalyzed epoxidation of 1-acetoxycyclohexene is a key step in a novel synthesis of catechol from cyclohexanone via the sequence465... 

The protonation of the steroidal enol ethers ( )-5.161 and (Z)-5.161 give diastereoisomeric products 5.162 and 5.163, respectively. Identify the features that explain why the geometry of the double bond appears to control the diastereoselectivity. 

Steroidal enol ethers have also been shown to undergo facile dehydrogenation with DDQ, but the products formed are dependent on the reaction conditions. Thus, whereas under anhydrous conditions the... 

Heathcock has reported an anomalous case of ozonolysis of a silyl enol ether. Usually these substrates undergo facile oxidative cleavage in the same manner as alkoies. However, in this instance the a-silyloxy ketone (61) was obtained in quantitative yield. The inteimediacy of a silyloxy epoxide was suggested. A more recent leport has indicated that a similar process is competitive with the simple cleavage reaction, (63a) versus (63b), in the ozonolysis of the steroidal enol ether (62). 

Difluorocarbene has also been added to a number of steroidal enol acetates, providing the corresponding acetoxy-difluorocyclopropane in good yield. Treatment of the latter with base constitutes a convenient homologation sequence which affords either the a-difluoro-ketone, or the a-fluoro-enone, depending on steric factors. Thus, difluorocarbene was added to the enol acetate (77) to give the a-difluoro-adduct (78). Treatment of (78) with methanolic potassium... 

Hydrolytic cleavage of the C-O bond of bicyclic, tetracyclic, and steroidal enolates with HF-SbFs induces their isomerization to the corresponding ketones (Scheme 14.41) [104]. Rearrangement of dienones to aromatic compounds is also promoted by HF-SbFs (Scheme 14.42) [105]. Ring expansion of methyl penicilli-nates is achieved by SbCls to give thiazepine derivatives [106]. 1,3-Dithianes derived from ketones and aldehydes are deprotected with SbCls by means of a single-electron-transfer mechanism [107]. 

Cyclic a,fi-unsaturated ketones.2 The anion reacts with the steroidal enol lactones (1) and (3) in THF under N2 to give the cyclic a,/3-unsaturated ketones (2) and (4) directly. 

An interesting example of the selective hydrogenation of the A5 double bond in the presence of a less reactive, extremely sterically hindered double bond is the regio- and diastereoselective hydrogenation of steroidal enol acetate 9,s. 

The hydrogenation of steroidal enol ether 3 show s that a double bond substituted with an alkoxy group is deactivated. The A5 double bond is hydrogenated in a completely diastereose-lective manner yielding preferentially the isomerized product 4, as well as some nonisomerized product24,... 

Ketosteroids may be converted to enol—TBDMS ether derivatives with t-butyidimethyliodosilane as a catalyst [103]. Steroid enol-TBDMS and mixed TBDMS-TMS derivatives have been appiied to the analysis of steroids in rat testes [104]. The enol-TBDMS mass spectra are characterized by the presence of intense M ions. 

In addition to the formation of m/z 143 by D-ring decomposition, fragments at m/z 142 and 143 are obtained from various steroid-TMS and steroid-enol-TMS by A-ring cleavage, e.g., steroids bearing a 3-hydroxy-androst-4-ene ° or 3-hydroxy-androst-l-ene nucleus (Table... 

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