Syntheses of the type BD

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 

A tricyclic analog of the corticosteroids (287) was also obtained from the keto acid (281). The Reformatskii reaction of the methyl ester of acid (281) with bromoacetic ester led to compound (284), the cyclization of the chloride of which yielded the tricyclic keto ester (283). Reduction of the keto group and the side chain with subsequent acetylation led to the diacetate (286), the oxidation of which with osmium tetroxide in the presence of N-methylmorpholine peroxide gave compound (287). The assignment of a configuration to the latter was made on analogy with the natural steroids [859-861]. 

The Stobbe condensation between the enol ether (299) and di-tert-butyl succinate with subsequent aromatization led to acid (317), which was converted through its chloride into the corresponding methyl ketone (318). 

The successive condensation of compound (318) with tert-butyl cyanoacetate, hydrogen cyanide, and acrylonitrile, and pyrolysis to eliminate the tert-butoxycarbonyl grouping, led to the trinitrile (321). Its intramolecular condensation by the Thorpe reaction gave the bicyclic product (320) which was 

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Model block-double graft copolymers and terpolymers of styrene, butadiene, and isoprene of the type poly[S-6-(PBd-l,2-g-X)] were recently synthesized (28), where X is either S, Bd, I, or S-6-I by a combination of anionic polymerization, hydrosilylation, and chlorosilane linking chemistry. The backbone P(S-6-l,2Bd) was synthesized by sequential addition of the monomers. The vinyl groups of the PBd-1,2 block were hydrosilylated with HSiCH3Cl2 and used for the attachment... 

Syntheses via BCD Intermediates with a Five-Mem-bered Ring D. These syntheses generally start from 6-methoxy-l-tetralone or its 5-methyl derivative, which are used as the BC fragments. All the methods used in Chapter II for the synthesis of estrogenic hormones from 14-oxa compounds are employed for the construction of ring D. It must be mentioned that some of the intermediates illustrated in Schemes 70 and 71 have also been obtained by syntheses of the BD - C type (cf. Section 3 of this chapter). 

Miura et aL terminated a living anionic polymerization of BD with several different types of nitroxides to prepare CRP initiators [283]. The bulk polymerization of St initiated by four different nitroxide moieties proceeded with a linear increase of the molecular weight with monomer conversion and molecular weight distributions <1.2. To synthesize the macroinitiators for preparation of... 

The imidazo[l,2-ft]pyrazole, imidazo[l,5-a]imidazole, imidazo[l,2-a]imidazole, imidazo[2,l- ]ox-azole, imidazol[2,l-6]thiazole, and imidazo[l,5-c]thiazole ring systems have all been prepared by more than one of the different types of synthetic route described in Sections 8.04,9 and 8.04.10. The various routes to each of these heterocycles are summarized in Table 4. For example, the imidazo[2,l-ft]thiazole skeleton has been synthesized by (5 - - 0) routes (types B, C, and D), (4 - - 1) routes (types BC and CD), and by (3 -I- 2) routes (type BD) (for a summary of this classification see Scheme 10). By far the most common route to this system is the (3 - - 2) ring closure discussed in Section 8.04.9.3.2. Tetramisole (34), the most important compound of this type in terms of commercial... 

Of the reported routes to imidazo[l,5-c]thiazoles, the (4 + 1) type BC and (3 + 2) type BD routes are more generally applicable and involve milder reaction conditions. Imidazo[l,2-Z>]pyrazoles can be obtained by both (5 + 0) syntheses (types B and C) and (3 + 2) syntheses (type BD). The (3 + 2) synthesis allows access to a range of 2,3-disubstituted heterocycles whereas the (5 + 0) type B route allows simple analogues to be synthesized from already functionalized aminopyrazoles. The (5 + 0) type C synthesis is limited in scope due to the multistep route to the required precursors. 

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