Syntheses of the type BC

The total steroid syntheses following this route can be divided into two groups. The first of them comprises syntheses through tricyclic BCD intermediates with a five-membered ring D. The second, quantitatively far smaller, group of syntheses uses as tricyclic intermediates compounds with a six-membered ring D, which makes necessary its subsequent transformation into a five-membered ring. 

The building up of ring D by Sarett s method with the successive introduction of amethallyl group at C 2 and an ethoxycarbonylmethylene group at Ci4 led via ketone (173) to compound (174), from which compound (176) was obtained by reduction of theCi4 chain, oxidation of the C13 side chain, and cyclization via the intermediate (177) the cis-C/D linkage in compound (176) was shown by its oxidation to the ketone (178) [762]. 

Me) [764]. This method has also been used to obtain analogs of (185) and (186) not containing methoxyl [765] or also containing a methyl group (185, 186 R = Me) [766]. 

In order to circumvent the difficulties arising in the use of methyl vinyl ketone, and to introduce a four-carbon residue into the molecule directly, the alkylation of the ketone (196), or, better, the ketone (195), or, still better, the pyrrolidine enamine (201) with 1,3-dichloro-2-butene has been carried out.t The product so obtained (200), with the desired 8j3-configuration, was converted by hydrolysis with concentrated sulfuric acid in the cold into compound (205) with a 3-oxobutyl residue in position 10. This compound is the main intermediate for further syntheses, since its double bond 

The stereochemistry of the catalytic hydrogenation of compound (205) depends on the pH of the reaction medium. In an alkaline medium, the Oof, 10q -structure is formed predominatly, and this epimerizes through the enolization of the 5-0x0 group into the 9a, 10/3 -structure (206). In an acid medium, a mixture containing a considerable amount of the, 10/3-epimer (210) was formed which, on saponification of the benzoyl group and cycliza-tion with acids, led to the 9/3,10a-isomer of 19-nortestosterone (211) [789]. Similarly, the cyclization and hydrolysis of the 9a, 10)3-isomer (206) gives the natural 19-nortestosterone (212) [61, 776, 796-800]. 

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