Syntheses of the type AB

Attention is attracted by the fact that practically all the successful syntheses from the precursors considered in this chapter (with the possible exception of syntheses of the type AB - CD) relate to derivatives of equi-lenin and estrone. This is connected with the nature of the reactions used for the syntheses of the missing rings. These include, in the first place, cyclizations with the participation of acids and ketones, which take place well only with aromatic rings or atoms of carbon activated by the propinquity of aromatic rings. 

Several total syntheses of estrogenic hormones and, in the first place, of derivatives of equilenin have been carried out by this route. The principles of the approach to total steroid synthesis considered in this chapter generally come up against serious obstacles even in their application to estrone derivatives. Moreover, their application to the synthesis of nonaromatic steroids has generally been unsuccessful. 

Syntheses via 0 4 Ketones with Aromatic Rings A and B, Tricyclic ketones containing the aromatic system of naphthalene have been used as the raw material for a number of total syntheses of equilenin which have remained the most successful even at the present time. 

Two methods of synthesis of the acid (5) from 6-methoxy-l-tetralone (8), formed in two stages from nerolin (7) [139-142], have also been proposed. One of them [143, 144], like that just described above, is based on the introduction of the and 0 2 atoms by the Reformatskii reaction of the ketone (8). The ester formed (10) is converted into the bromide (11) and the 0 3 and 0 4 atoms are introduced by the condensation of the latter with sodiomalonic ester and decarboxylation. Dehydrogenation of the resulting acid (12) gives the acid (5). According to the other method for synthesizing this acid [140], the acids are introduced in one stage 

The final stage, the cyclization of acid (5) to form Butenandt s ketone (6), is carried out either via the acid chloride under the action of stannic chloride [137, 144] or from the acid as such by the action of hydrofluoric acid (yield 85%) [140] or 90% sulfuric acid (yield 87%) [143]. The synthesis of analogs of the ketone (6) containing no 3-methoxy group has also been described [145, 146]. 

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The main methods for the total synthesis of steroids by this type of method of constructing the skeleton repeat those used in syntheses of the type AB (see Chapter II, Section 3) with the difference that instead... 

Syntheses from AB and AC Fragments. A considerable number of investigations has been devoted to the perfection and subsequent development of syntheses of the type AB - C described in Schemes 35-39. We must first mention work on the improvement of methods of obtaining the main starting materials, 2-aligrl-l,3-cyclo-pentanediones, both by the intramolecular acylation of y-keto acids [1073, 1074] and by the reaction of succinic anhydride with ketone enol acetates [1075] and with alkylacetic acids [1076] in the presence of AICI3. 

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