In the total synthesis of steroids on the industrial scale, three factors are important: stereoselectivity of the reactions used, resolution of' racenzic intermediates at the earliest possible slage, and convergence ofthe synthesis. Theoretical advances and wider practical experience in the chemistry 0fpoI)xyclic compounds have recently led to the development 01 ihe first syntheses which are suitable for tlie industrial production of steroid hormones.Arigew. Chem. intermit. Edit. / VoI. 4(1965) Nu. 3
Bei der Totalsynthese von Steroiden im industriellen Maßstab müssen vor allem drei Faktoren berücksichtigt werden: Stereoselektivität der angewendeten Reaktionen, möglichst frühzeitige Racematspaltung eines Zwischenproduktes und Konvergenz des Syntheseschemas. Die Entwicklung der Theorie zusammen mit vertieften praktischen Erfahrungen in der Chemie polycyclischer Verbindungen haben in letzter Zeit die ersten industriell verwertbaren Synthesen von Steroidhormonen ermöglicht.
As can be seen from the above scheme, the compounds (70) and (71) are also obtained as by-products in the synthesis of ynamines from t-butylchloroacetylene and trimethylamine (which is described in Section 3.4.). On slow addition (to avoid amide chloride formation and side reactions) of strong acids to the ynamine (72), the only product formed in the presence of tertiary amines, e.g. dimethylaniline, is the saIt (73) The cyclobutene cyanine can be readily synthesized in the presence of HBF4 even without special precautions [49,611, possibly because the weakly nucleophilic BF4Q anion makes the conversion of the keteneiminium structure (65) into the less polar enamine structure (66) impossible.A number of phenylethynyldialkylamines react smoothly with strong acids to form the corresponding cyanines, which can be converted into bromine derivatives (73) by treatment with N-bromosuccinimide (NBS); (73) can also be obtained by direct bromination of the ynamine in dioxane [53J:Bromination of the t-butylethynylamines instead of the phenyl compounds leads to :only the allene aniidinium salts (74) in yields of up to 87 %; this is apparently due to steric factors 1531. From a technical or economic point of view the total synthesis of sterically intricate. carbon compounds has become so important that a new field of preparative stereochemistry has been established which embodies a number of specially developed techniques. This is especially the case in the syntheses of alkaloids and antibiotics, and above all in the plant-scale production of hormonal steroids [I].
Dieser Aufsatz berichtet an Hand zahlreicher Beispiele über die stereoselektive Bildung organischer Verbindungen. Als Beispiele dienen besonders Alkaloide und Steroide, deren Synthese auch technisch interessiert. Eine asymmetrische Synthese, welche die umständliche und verlustreiche Racematspaltung überflüssig macht, ist erst in wenigen Fällen gelungen. Verfahren zur Konfigurationsänderung und zur Racematspaltung werden ebenso besprochen wie die Planung einer vielstufigen stereoselektiven Synthese.
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