Syntheses of the type CD

Syntheses by this route are conveniently grouped in accordance with the classes of steroid compounds synthesized. They are used mainly for two purposes to obtain estrogenic hormones and, from these, 19-norsteroids, on the one hand, and to obtain derivatives of vitamin D, on the other hand. In the latter case, obviously, the necessity for cyclization with the formation of ring B is absent, and the ACD fragments obtained are the final products of the synthesis. Total syntheses of 8- and 9-azasteroids are also considered individually in this section. 

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The contents of the second section (syntheses of the AB - CD type) include the condensation of vinylbicyclenes with cyclic dienophiles. Among these, the successful total synthesis of estrone (Scheme 19) and the synthesis of nonaromatic D-homosteroids (Scheme 22) deserve to be mentioned. ... 

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. 

Crystal structures of the benzotriazole complexes [Zn(HL)Cl2] and [Zn2L4] (HL = benzotriazole 62) have been reported the former compound has the metal in a tetrahedral N2C12 environment (Zn—N, 2.014, 2.034 A Zn—Cl, 2.241, 2.235 A) and the latter is a polymeric species.441 The complex [H2L]2[ZnCU] (HL = 62) has also been described it is isostructural with the tetrachlorocobaltate(II) analogue, which has previously been structurally characterized.441 The synthesis and powder diffraction pattern for [ZnL Cy (L = 62) have also been reported.442 Complexes of the type MX2L2 (M - Zn, X = Cl, Br, I or SCN M = Cd, X = Cl L = allyl or 3,5-dimethylpyrazole) have been synthesized where L is 3,5-dimethylpyrazole, cadmium also forms the complexes (CdBr2L3 and CdI2L4. When L is allylpyrazole, alkene coordination is not observed thiocyanate is N-bonded.443,444... 

Many examples of electrochemically prepared anionic complexes are known [202,506,507,551]. Among them, the coordination compounds with ammonium cations are of interest [506,507]. In these syntheses, it is possible to vary the composition of complexes of the type [(R4N)mMX ]. Thus, similar complexes (R = Me, X = SCN, m = 2, 3, 4 m = 4, 6) were obtained by dissolution of metals (Mn, Fe, Co, Cu, Zn, Cd) in aqueous medium, containing (Me4N)SCN [561], Analogous syntheses with use of pyridine, 2,2 -bipy, and 1,10-phen (L) lead to neutral complexes, for instance (3.241) [561] ... 

Complexes of the type MX2L2 (M = Zn, X = Cl, Br, I, or SCN M = Cd, X = Cl L = allyl or 3,5-dimethylpyrazole) have been synthesized where L is 3,5-dimethyl-pyrazole, cadmium also forms the complexes CdBr2L3 and Cdl2L4. When L is allylpyrazole, olefin co-ordination is not observed thiocyanate is N-bonded. ... 

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