Organic Lab Reactions 189

Organic Lab Reactions 189 - out for a short time, only the...

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184 REDUCTION WITH ALUMINUM ALKOXIDB8 method for protecting one ketonic group while another is reduced has been applied to androstenedione (X). 20 This compound was converted into the 3-pinacol (XI) with sodium amalgam and then reduced by aluminum isopropoxide UT?81% yield to the pinacol (XII) of testosterqne. Treatment of the latter 1,2-glycol with lead tetraacetate regenerated the ketone group with cleavage of the molecule to give testosterone (XIII). II J xn Two interesting examples of partial reduction without any protection of either carbonyl group have been described. A 70% yield of a mixture of w's- and irans-testosterone (XIII) was obtained by reduction of androstenedione (X) with aluminum 2-butoxide in s-butyl alcohol, 21 The remainder of the material consisted of unreacted diketone as well as some of the corresponding diol. Several selective reductions have been successful with porphyrin derivatives. 22 When the reduction was carried
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Unformatted text preview: out for a short time, only the aldehyde group in the methyl ester of meso-pyropheophorbide b (XIV) was reduced, and the ketone group in the molecule was unaffected. This selective reduction is.reported to depend upon the use of pure aluminum in preparing the isopropoxide. Tech-nical aluminum containing traces of copper and zinc brought about some reduction of the ketone group as well as the aldehyde group. In view of these encouraging steps toward selective reduction of one carbonyl group in the presence of others, more work along these lines is desirable. It must be pointed out that the last two reductions were carried out with very special types of molecules, and that other examples 20 N. V. Organon, Fr. pat, 842,940 (June 21, 1939) [Chem. Zentr. (I), 429 (1940)]. 81 Miescher and Fischer, Helv. Chim. Ada, 23, 168 (1939). "Fischer, Mittenzwei, and Hev6r, Ann., 645, 154 (1940)....
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