Tricyclic compounds Cope rearrangements

DMAD get thermally converted to quinolones (66), through a Cope rearrangement. These quinolones give rise to tricyclic heteroaromatic compounds, namely, pyrano[3,4-6]quinoline-l,5-diones (67) and furo-[3,2-c]quinolines (68), depending on the reaction conditions (Scheme... 

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)."... 

Tricyclic compounds result when in intramolecular cyclopropanation/Cope rearrangements the double bond of the diene moiety next to the tether is incorporated in a ring, e.g., formation of 122 and 124878. 

Cycloaddition reactions of two-co-ordinate phosphorus compounds described this year includes the [2 + 2] cycloaddition of an iminoborane to aminoimino-phosphines to give 1,3,2,4-diazaphosphaboretidines (125). In an attempt to prepare hydrazino-bis-phosphaalkenes (126) as new candidates for hetero-Cope rearrangements, the tricyclic compounds (127) were obtained. The result is explained by a Diels-Alder rearrangement of (126), as shown. 

Compared to the example above, the participation of benzene in the aromatic-Cope rearrangement has been more difficult to achieve. However, it has recently been utilized for the preparation of helicenes and other polycyclic compounds.One of the first and most impressive demonstrations of this reaction was utilized in the synthesis of tricyclic compounds such as 252. As above, the anionic oxy-aromatic-Cope rearrangement of 251 proceeded in excellent yield to give 252, resulting from rearomatization of the benzene ring. 

Novel spirocyclic compounds have been prepared by the Cope rearrangement of taxane-like tricyclic compounds having a 1,5-diene moiety. The transformation was found to be reversible and the product distribution was found to be greatly dependent on the solvent polarity. The intramolecular cyclopropanation of dienylmethyl vinyldiazoacetate, followed by a Cope rearrangement, has been used in the... 

Intermediate 1-6 can evolve by metal loss to give tricyclic compound 1-2, or by fragmentation to form methyl ketone 1-3 (Scheme 2.2). The competitive 2-oxonia-Cope rearrangement of intermediate 1-6 via 1-7 forms 1-8, which results in the minor epimer 1-2 of the tricychc compotmd. As other gold(I)-catalyzed reactions of enynes, this reaction is stereospecific [Refs. 4, 8, 154 in Chap. 1] [1]. 

To date, the stereocontrolled synthesis of the tricyclic vinigrol core was only achieved through the use ofpericyclic reactions. In 1993, Hanna et al. disclosed the first synthesis of the tricyclic core of vinigrol 92 (Scheme 8.13) [35]. Their approach features an intermolecular Diels-Alder reaction between cyclic diene 87 and 1,4-benzoquinone 88 to give tricycle 89, which upon treatment with NaBH afforded 90 in 62% over two steps. After functional group manipulations, compound 91 underwent an anionic oxy-Cope rearrangement to deliver 92 in 82% yield. 

The cytotoxic sesquiterpenoid quadrone, 38, has an embedded diquinane carbon framework that allowed the Piers s group to leverage the chemistry of the Weiss-Cook reaction. The monoketal 35 is readily available from 12 (R = R" = H). Several transformations converted this compound into the vinyl cyclopropane 36. Thermal rearrangement of the scaffold employing a Cope process afforded tricyclic 37. This compound was readily elaborated into 38. 

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