Ergosterol acetate

Another example of selective deuteration in homogeneous solution is saturation of the sterically more accessible A -double bond in ergosterol acetate (142 143). The a-configuration of the incorporated deuteriums... 

Scheme X.5. The mechanism proposed for the peroxidation of ergosterol acetate by HiOr-FcCb in pyridine,...

Protection of the ring-B diene system in ergosterol acetate (390) as its adduct (391), followed by bromination of the C-22 double bond to (392) and dehydro-bromination with l,5-diazabicyclo[4,3,0]non-5-ene (DBN) in toluene, gave ergosta-5,7,22,24(28)-tetraen-3)8-ol acetate (393). 

Addition of deuterium to ergosterol acetate was shown to form the 5a,6a-dideuterio reduction product under mild conditions (Equation 15.4). This result illustrates a number of features of the reactivity of Wilkinson s catalyst. First, the conjugated diene is reduced in preference to the C21-C22 double bond. Second, the diene is reduced from the less-crowded a-face of the steroid. Neither the remaining trisubstituted double bond nor the trans disubstituted A double bond are affected. Finally, no isotopic exchange takes place during this reaction. This selectivity has been used to specifically label prostaglandins with tritium (Equation 15.5). The sensitive 3-keto alcohol is unperturbed. 

In 1931, it was shown by Reindel and Kipphan that ozonolysis (Oj) of ergosterol acetate in petroleum ether-ethyl acetate produced a mixture containing 2,3-dimeth-ylbutanal, thus identifying the side chain and the position of the double bond therein (Equation 13.3). 

In 1951, Jeger and coworkers reported (as shown in Scheme 13.32) that they had converted ergosterol acetate (by now clearly written as the A -triene acetate) into A 22-3p-acetoxyergostadiene (a so-called a-dihydroergosterol acetate) by reduction of the acetate of ergosterol with sodium in ethanol. When the diene was oxidized... 

The structures of the adducts of ergosterol acetate and maleic anhydride, the first of which were isolated by Windaus and Lutringhaus in 1931, have been revised. 8 Qne is a normal adduct of endo configuration, in which the dienophile addition has occurred from the a-side. The others are produced by an addition at C-7 and concomitant abstraction of either the 9a or the 14a hydrogen to give the 7a-succinic anhydride derivatives of 3p-acetoxy-5,8,22-triene and 3p-acetoxyergosta-5,8 (14), 22-triene. Similar addition to the diene system with acrylonitrile and dimethyl diazodicarboxylate has been observed.85... 

Winterfeldt and co-workers discovered that ergosterol acetate 35 can be used to prepare macrocycle 37 by Diels-Alder/retro-Diels-Alder reactions. Cycloaddition of ergosterol acetate 35 to propargylic aldehyde in the presence of tungsten hexachloride as a Lewis acid catalyst produced a.jS-unsaturated aldehyde 36. When it was heated in toluene, the macrocyclic benzaldehyde 37 was obtained in 85% yield (Scheme 16.5). This skeletal... 

Sensitizer of Photooxygenation. Barton showed that oxygen, in the presence of trityl fluoroborate and ordinary light, adds to cisoid dienes at —78 °C in very high yields. For example, the peroxide of ergosterol acetate is formed in quantitative yields under these conditions (eq 10), which have been used also for photocycloreversions of cyclobutanes. ... 

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