Other Reactions of Unsaturated Steroids

Other Reactions of Unsaturated Steroids.—Allylic alkylations catalysed by palladium have been reviewed and steroid examples are incorporated.48 The full 

Kocovsky and V. fcemy, Collect. Czech. Chem. Commun., 1980, 45, 3030. 

7r-allyl pyridine complexes.51 Oxidation of 7i-allyl palladium complexes with CrVI in DMF-ether containing a trace of sulphuric acid was reported to give the corresponding a,p-unsaturated ketones and is exemplified by the conversion of the complex (37) into 5a-cholest-2-en-l-one and 5a-cholest-l-en-3-one.52 

Reaction of Fe(CO)5 with the epoxy-vinylcholestane (38) gave the complexes (39) and (40) which were oxidized with CeIV ammonium nitrate, the former giving a mixture of the lactones (41) and (42) and the latter giving only the 8-lactone (42).53 

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Other Reactions of Unsaturated Steroids.—A review on organopalladium intermediates includes several steroidal examples. A mechanistic study of the formation of the 7r-allyl palladium complex (65) from the corresponding 3-oxocholest-4-ene led to the conclusion that initial 7r-complexing was rate limiting. Reactions of a series of similar ir-allyl palladium complexes (66)—(68) with dialkyl malonate ion gave the 3-oxo-A -6/S-yl malonates (69)—(71) respec-... 

Other Reactions of Unsaturated Steroids.—Asymmetric synthesis of optically active tricarbonyliron complexes of 1,3-dienes was achieved using the tricar-bonyliron complex (25) as a transfer agent for Fe(CO)3. Further investigation of the stereochemistry of formation of a-(4-6i7)-PdCl complexes from A -3-oxo-... 

Electrophilic Addition Other Addition Reactions Reduction of Unsaturated Steroids Oxidation and Dehydrogenation Miscellaneous Reactions... 

Simultaneous oxidation of two alcohol functionalities can be performed in both saturated and unsaturated compounds. For example, oxidation of diol 24 was achieved in 30% yield to give diketone 25.33 Steric factors can play a large effect and can result in other reaction processes, such as rearrangement.3 Oxidation of saturated steroid 26 (R = C6H11O2) furnishes diketone 27, with inversion taking place at C-5,39 whereas oxidation of unsaturated steroid 28 (R = C8H17) also yields diketone 27, in which the double bond has been formally reduced.40 The oxidation of steroids containing two cis alcohols at the C-3 and C-5 positions is hindered by the formation of an unreactive aluminum chelate.41... 

With the exception of the parent compounds, where the Michael adducts are isolated, acrylic esters [see, e.g. 6,7,31,105,111 ] and nitriles [6,7], and vinyl ketones [26, 113, 115] generally yield the cyclopropanes (Table 7.6) under the standard Makosza conditions with chloroform. Mesityl oxide produces a trichlorocyclopropy-lpropyne in low yield (10%) [7]. When there is no substituent, other than the electron-withdrawing group at the a-position of the alkene, further reaction occurs with the trichloromethyl anion to produce spiro systems (35-48%) (Scheme 7.12) [7, 31]. Under analogous conditions, similar spiro systems are formed with a,p-unsaturated steroidal ketones [39]. Generally, bromoform produces cyclo adducts with all alkenes. Vinyl sulphones are converted into the dichlorocyclopropane derivatives either directly or via the base-catalysed cyclization of intermediate trichloromethyl deriva-... 

Cytochromes P450 are monooxygenases whose cosubstrates, often NADH or NADPH, deliver electrons to the active center heme via a separate flavoprotein and often via an iron-sulfur protein as well 476a b A typical reaction (Eq. 18-55) is the 11 (3-hydroxylation of a steroid, an essential step in the biosynthesis of steroid hormones (Fig. 22-11). The hydroxyl group is introduced without inversion of configuration. The same enzyme converts unsaturated derivatives to epoxides (Eq. 18-56), while other cytochromes P450... 

The base-catalysed methylation of other unsaturated steroid ketones is determined both by their ease of enoHsation and also by the accessibility of the reaction site to the bulky methylating species. Cholest-5-en-7-one reacted in a manner analogous to cholest-4-en 3"0ne, giving the 6,6-dimethyl compound (17) [172], and other unsaturated ketones (A8b >-i5-one A -ii-one [X73], and A i >-7-one [174]) each... 

Lanostan-3j8-yl azidoformate (248) and its A -unsaturated derivative are thermolysed or photolysed to give the oxazolidinones (249) and the products (250), functionalized in the 4a-methyl group. Other reactions leading to heterocyclic derivatives of steroids are described on p. 305. 

The reduction of a. -unsaturated carbonyls with lithium in ammonia is a versatile reaction of great utility. The advantage of this method is that regiospecific enolates are obtained that are sometimes not accessible by other routes. This technique finds important applications in steroid-like systems (equation 15). °... 

The electrophilic addition reactions of A -unsaturated steroids and other rigid cyclohexenes are controlled mainly by the conformational preference for diaxia) addition HOBr, for example, gives mainly a 5a-bromo-6)5-alcohol. A study of similar reactions with B-nor-A -unsaturated steroids suggests that the reaction of a cyclopentene is under electronic rather than conformational control.A variety of reagents (HOBr, BrF, Brj, BrOMe, and BrOAc) gave mainly 6a-bromo-5)S-substituted derivatives (155), indicating that the initial product, a 5a.6a-bromonium ion (154). reacts further according to Markovnikoff, with attack of the anion at the tertiary 5 -position. 

It is well established that liver microsomes in the presence of NADPH and in the absence of chelator are capable of oxidizing cholesterol and other 3P-hydroxy 5-unsaturated steroids yielding the common autoxidation products 3-8 [16]. In this case, the cholesterol oxidation is secondary to the enzymatic NADPH-dependent lipid peroxidations. The enzyme-catalyzed reaction is required, however, merely to reduce Fe i to Fe which in turn catalyzes ordinary autoxidation. It has also been shown by EPR studies using spin traps that radicals are involved in these conversions [16]. The major radicals detected were lipid peroxyl radicals and superoxide, whereas only small amounts of hydroxyl radicals were... 

All unsaturated steroids, as well as many other unsaturated polycyclic compounds, display a series of colors if treated with cold mineral acids (Fieser and Fieser, 1949, p. 100). The lipid droplets in thecal and lutein cells of the ovary were found to color if treated with sulfuric acid (Dempsey and Bassett, 1943 McKay and Robinson, 1947). Dempsey and Wislocki (1944) observed a positive reaction also in the syncytium of the placenta. Chester Jones and Deane (1949) obtained positive reactions with a number of steroid hormones that had been dissolved in oil, suspended in gelatin, and spread on slides. 

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