Keto aldehydes rearrangement

The blank test in liquid phase yields less than 1% conversion. Unlike non-zeolitic catalysts, except for H-Nafion, most zeolites yield complete conversion. A high yield of the keto aldehyde 24 up to 81%, was surprisingly attained by using H-FER as a heterogeneous catalyst. For the rearrangement of isophorone oxide, the presence of acidic sites is necessary for the catalytic activity. The reactivity of H-FER can be explained by the acidic outer surface of the catalyst Molecular modeling showed that the isophorone epoxide is too bulky for the small pore size of ferrierite. 

The cytotoxic sesquiterpenoid (-)-quadrone, isolated from the fungus Aspergillus terreus, possesses the constitution and absolute stereochemistry shown in (218). The tricyclic carbon skeleton of this interesting natural product is the same as that found in compound (198), which, as described above (Scheme 28), is readily prepared by thermolysis of the tricyclic diene (197). Thus, it appeared that the Cope rearrangement of a suitably substituted and functionalized derivative of (197) might serve effectively as a key intermediate in a total synthesis of ( )-quadione (218) that is, successful Cope rearrangement of a substrate, such as (219), would provide, stereoselectively, the tricyclic substance (220). Presumably, the intermediate (220) could then be converted into the keto aldehyde (221), which had already been transformed into ( )-quadrone (218). ... 

A successful formal total synthesis of ( )-quadrone (218) via a route in which a divinylcyclopropane rearrangement played a key role was achieved by employing the substrate (228 Scheme 32). This material is readily prepared from the ketone (227) and, in contrast to compounds (219) and (224), undergoes smooth Cope rearrangement to the tricyclic diene acetal (229), which is easily transformed into the keto acetal (230). A rather lengthy sequence of reactions effects conversion of (230) into the keto aldehyde (221), which, as mentioned previously, has served as an intermediate in a total synthesis of ( )-quadione (218)."... 

Translation of these results into compound I leads to structure X. Unraveling of the strained zwitterion XI derived from this would yield keto aldehyde XII, a structure that plays a central role in the various possible reaction mechanisms that branch off from the starting material I. Furthermore, under photo-lytic conditions, some alkenes react with carbonyl compounds to form four-membered cyclic ethers, namely, oxetanes, by way of a [2-1-2] cycloaddition reaction known as the Patemo-Buchi process. Such a reaction would be all that is necessary to convert XII into the bicyclic cyclopropanone XIII required for the Favorskii-type rearrangement (see Scheme 42.3). Splitting by methanol attack would directly yield compound II. 

It has been suggested" that the formation of the keto-aldehyde (137) in relatively high yield from the sensitized photo-oxidation of thujopsene (138) can best be explained in terms of a dioxetan intermediate (139), similar examples of which have recently been found in singlet oxygen addition to electron-rich double bonds. An extensive analysis of the products of acid-catalysed rearrangement of thujopsene (138) has been carried out." Under different acid conditions ten products have been isolated and identified these include the known compounds, chami-grene (140), cuparene (141), and widdrol (142 R = H) together with the previously unknown compounds (142 R = Et) and (143)—(148). The authors have put forward a mechanistic scheme to explain the formation of all these compounds based on interconversions of cyclopropylcarbinyl and homoallyl cations. 

The thio-Claisen rearrangement has its special value when the specific reactivity of a sulfur function, e.g. its carbanion-stabilizing effect or the high nucleophilicity of S, can be utilized, as in syntheses of 7-keto aldehydes (Scheme 72) or thioamides (Scheme 73). ... 

When the initially formed rearrangement product is a p-keto aldehyde, facile loss of the formyl group is sometimes observed (retro-aldol). An interesting example is found in the reactions of the quinone derivative (129 equation 53) Rearrangement accompanied by deformylation occurred under a variety of acidic conditions, but the BFs-induced reaction was especially efficient. ... 

A Fannitalia group" reported, without details or yields, that both the a- and j3-epoxides derived from testosterone are rearranged by BFs-etherate in benzene to 4-hydroxy-A -3-ketones. Collins (Australia) made a more detailed study in the cholestane series and found that both the a- and the fi-oxide indeed give the hydroxy-A -cholestene-3-one but that they both yield a second product characterized as 5/8-A-norchoIestane-3-one. TTie latter compound evidently comes from an intermediate /3-keto aldehyde, probably by deformylation during chromatography on neutral alumina. 

Analogous pyrrolyl derivatives are also found as furan metabolites. Furans are oxidized by CYP to reactive furan-epoxides, which rearrange to ene-dial or ene-keto-aldehyde metabolites (Figure 33.20). After... 

Terpene epoxides are very reactive compounds. Some are prepared conventionally by isomerization using homogeneous catalysts such as Bp3.Et20 [35,36]. The rearrangement of isophorone oxide (Figure 6) yields the keto aldehyde (13), which is an intermediate for fragrance chemicals. If the reaction is performed in the presence of zeolites the keto aldehyde (13) and the keto-enol form of the a-diketone... 

Conversion of X to the C-17 ketone (XIII) is considered as a reverse aldol reaction. Conversion of the keto-aldehyde (XIV) to the hydroxy acid (XV) is considered a benzillic acid rearrangement. 

P,7-Unsaturated ethers of cyanohydrins, on formation of lithio derivatives, undergo a 2,3-sigmatropic rearrangement to form. y-unsaturated ketones (equation 21), whereas benzylic ethers of aliphatic cyanohydrins gave o-methylaryl ketones. The method has been used to prepare 3-methyi-l-(3-methyl-2-furyl)-l-butanones, a naturally occurring Cio terpene, a-allenic ketones and enolic monoethers of 7-keto aldehydes via 2,3-sigmatropic rearrangement of tiieir respective carbanions. ... 

Condensation of the enol ethers of P-dicarbonyl compounds with dimethylsul-phonium methylide generally takes place by attack on the carbonyl group, leading to furans. However, enol ethers derived from P-keto-aldehydes are attacked first at the double bond to give cyclopropanes. These further react at the carbonyl group, the resulting cyclopropyl epoxides rearranging to dihydropyrans (Scheme 1). 

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