Oxidation enol, chromium trioxide

For the synthesis of (69), the enol ether (71) from the indanone (70) was carboxylated with COa-n-butyl-Iithium in THF at —70 C to yield (72). The methyl ester (73) was converted into (75) via the maleic anhydride adduct (74), essentially as described in earlier work. Lithium aluminium hydride reduction followed by oxidation with dicyclohexylcarbodi-imide afforded the aldehyde (76). This was condensed with excess (77) to yield a mixture of the diastereomers (78). Oxidation with chromium trioxide-pyridine in methylene dichloride gave (79), which could be converted into the diketone (80) by treatment with excess benzenesulphonylazide. The diketo-lactam (81) was prepared from (80) as described for the synthesis of the analogous intermediate used in the synthesis of napelline. Reduction of (81) with lithium tri-t butoxyaluminohydride gave the desired dihydroxy-lactam (82). Methylation of (82) with methyl iodide-sodium hydride gave (83). Reduction of this lactam to the amine (84) with lithium aluminium hydride, followed by oxidation with potassium permanganate in acetic acid, gave (69). 

Steroidal 17-cyanohydrins are relatively stable towards chromium trioxide in acetic acid (thus permitting oxidation of a 3-hydroxyl group ) and towards ethyl orthoformate in ethanolic hydrogen chloride (thus permitting enol ether formation of a 3-keto-A system ). Sodium and K-propanol reduction produces the 17j -hydroxy steroid, presumably by formation of the 17-ketone prior to reduction. ... 

Oxidation of ecgonine (2) by means of chromium trioxide was found to afford a keto acid (3). This was formulated as shown based on the fact that the compound undergoes ready themnal decarboxylation to tropinone (4)The latter had been obtained earlier from degradative studies in connection with the structural determination of atropine (5) and its structure established independently. Confirmation for the structure came from the finding that carbonation of the enolate of tropinone does in fact lead back to ecgonine. Reduction, esterification with methanol followed by benzoylation then affords cocaine. 

Oxidation of 172 with chromium trioxide in pyridine gave the monoketone 176, whereas oxidation of spiradine F under the same conditions afforded the hydroxylactam 177. Catalytic hydrogenation of compound 176 afforded the a-ketol 178. The latter was treated with sodium methoxide in benzene to give an enolated a-diketone (179), which definitely fixed the position of the hydroxyl group at C-6 in spiradine G. Comparison of an ORD curve of compound 178 with that of 5a-cholestane-6-one established the indicated absolute configuration for these alkaloids. It is worth noting that these alkaloids bear many structural similarities to the earlier mentioned alkaloid ajaconine. 

Various complex and low yield procedures for the preparation of acetylallene have been described oxidation of homopropargytic alcohol with chromium trioxide in sulfuric acid,11 mild acid hydrolysis of conjugated ethoxyenyne,12 reaction of propargyltrimethylsilane with acyl halide,13 flash vacuum thermolysis of 0-keto trimathylsilyl enol ether14 and cydoelimination of p-silylethyl sulfoxide.15... 

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