Esters with chromium trioxide

An alternate route to the 5,7-diene system is by the hydride induced decomposition of A 7-toluenesulfonylhydrazones (113) (31, 41). The corresponding 7-oxo-steroids (114) can be prepared by allylic oxidation of A -sterol esters with chromium trioxide-amine complexes in methylene chloride at room temperature (163). The attractive feature of this method is that the product formed in the toluenesulfonyl hydrazone decomposition is virtually free of the 4,6-diene isomer. 

This oxidation has been used to determine the anomeric nature of sugar residues in oligosaccharides.153 The oligosaccharide is reduced to the alditol, this is acetylated, and the ester is treated with chromium trioxide in acetic acid in the presence of an internal standard. From the sugar analysis of the product, the residues that have survived (and, consequendy, are a-D-linked) may be identified. The... 

The synthesis of isolongistrobine also started with the imidazole ester 126, which in three steps was converted to the amino alcohol 129. Acylation with 4-pentenoyl chloride gave the amide alcohol 133. Oxidation of 133 with chromium trioxide in aqueous pyridine yielded the 4-pentene carboxamide 134. Oxidative splitting of the vinyl group of 134 with sodium periodate... 

The oxidation of unsaturated esters to unsaturated keto esters is accomplished with chromium trioxide in acetic acid and acetic anhydride. Methyl 2-nonenoate is thus converted in benzene solution at 0-20 °C into methyl 4-keto-2-nonenoate in 86% yield [553],... 

Oxidation of VI with chromium trioxide in acetic acid gave a methyl keto ester VII from which benzoic acid was eliminated under mild conditions to give an a,j8-unsaturated methyl ketone. When air was bubbled into an alkaline solution of the a,j8-unsaturated ketone it was... 

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). 

In contrast to the usual reaction of aromatic aldehydes with cyclic ketones o-nitrobenzaldehyde condenses with 17-ketones to produce good yields of seco-acids, a reaction which has been applied to the preparation of 16-oxa-steroids. Thus, 3 -hydroxy-5a-androstan-17-one or its acetate affords the seco-steroid (153), which can be oxidised either as the free acid by ozone and alkaline hydrogen peroxide to the diacid (155) or, as its methyl ester (154), with chromium trioxide to the monomethyl ester (156). Diborane reduction of the diacid (155) or lithium aluminium hydride reduction of the dimethyl ester (157) gave the trans-diol (158), cyclised with toluene-p-sulphonic acid to 16-oxa-androstan-3)5-ol (159) or, by oxidation with Jones reagent to the lactone (152) (as 3-ketone) in quantitative yield. This lactone could also be obtained by lithium borohydride reduction of the monomethyl ester (156), whilst diborane reduction of (156) and cyclisation of the resulting (151) afforded the isomeric lactone (150). The diacid (155) reacted with acetic anhydride to afford exclusively the cis-anhydride (161) which was reduced directly with lithium aluminium hydride to the cis-lactone (160) or, as its derived dimethyl ester (162) to the cis-diol (163) which cyclised to 16-oxa-14)5-androstan-3) -ol (164). 

Oxidation of lappaconitine with chromium trioxide in acetone followed by basic hydrolysis afforded a lactam-cyclopentanone. The identical lactam was also obtained by the oxidation of lappaconine with chromium trioxide in acetone. Only a vicinal diol (C-8 and C-9) could give rise to such an oxidation product thus, Yunusov and his colleagues (109) assigned the N -acetylanthranilic ester moiety to the C-4 position in lappaconitine. Recently, we have confirmed (110) this assignment by 13CNMR analysis of lappaconitine (87) and lappaconine (86). 

In 1952, Frank B. Colton (1923-2003) at Searle synthesised and later patented norethynodrel, an isomer of norethisterone. An improved synthesis emerged, in which both compounds were obtained, while the aromatisation and Birch reduction could be avoided. [41,42] As starting point serves 5-androsten-3/l-ol-17-one acetate, to which hypochlorous acid is added. Notable is the thermal or photochemical functionalisation of C-19 with lead tetraacetate/iodine, [43] under formation of a cyclic ether. Hydrolysis ofthe ester and oxidation with chromium trioxide leads to a A -enedione, while HCI is eliminated. Reductive opening ofthe ether gives the 19-hydroxy-compound, which can be oxidised with chromium trioxide to the lOjS-carboxylic acid and then decarboxylated in... 

The alcohol undergoes nucleophilic addition to chromium trIoxIde, to give a chromate ester which collapses In an elimination reaction to the aldehyde this aldehyde Is In equilibrium with Its hydrate, formed by the addition of water the carboonyl group, and the oxidation process with chromium trIoxIde Is repeated, to give a carboxylic acid. 

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