Heptacycles

Willstattcr s formula for tropine was confirmed by his syntheses of tropidine, tropine and 0-tropinc from the heptacyclic ketone, suberone as a starting-point. The latter was converted into the oxime, whieh was... 

The path to the complex heptacycle 87 (Scheme 17 a) commences with a stereoselective Wittig reaction between 2-deoxy-D-ribose (110) and (ethoxycarbonylethylidene)triphenylphosphorane (see Scheme 21). This reaction takes advantage of a ring-chain tauto-... 

The same pattern of reaction has been employed with symmetrical starting materials 124 and 126 to give tandem cyclizations yielding heptacyclic products 125 (Equation 29) and 127 (Equation 30), the latter being formed in near quantitative yields <1997KGS660>. 

We have recently characterized the heptacyclic alkaloid chilocorine from the ladybird (coccinellid) beetle Chilocorus cacti (23). In spite of its superficial complexity, this structure is easily dissected into two tricyclic moieties, A and B, each of which can be regarded as an acetogenin which has been elaborated from a straight chain of 13 carbon atoms stitched together at three points by a trivalent nitrogen atom. 

The second Chilocorini species studied, Chilocorus cacti, contained several alkaloids closely related to the former. The structure of the heptacyclic chilo-corine A (19) was deduced from a series of NMR experiment (DEPT, HMQC, DQ-COSY, TOCSY) and from a comparison of its spectral properties with those of exochomine (18) from which it differ by having two C-C linkages between the two tricyclic partners. However, the configuration at the asymmetric center in the azaacenaphthylene ring was not established [33]. 

Finally, the examination of Chilocorus renipustulatus, a European member of the Chilocorus genus, led to the isolation and structure determination of chilocorine D (22), a new heptacyclic alkaloid constituted of a hippodamine moiety linked to a modified octahydro-azaacenaphthylene skeleton encompassing a seven-membered ring [36]. 

In the last ten years, research in the field of insect defensive chemistry has made remarkable breakthroughs which would not have been possible without the advances in separation techniques, structure determination methods, and synthetic methodology. The structures of structurally complex compounds can now be determined on less than 1 mg of material, as exemplified by the hexa- and heptacyclic coccinellid alkaloids. Moreover, in-depth investigations on the biosynthetic origins of some of the defensive compounds are now made possible and will surely bring interesting data in the future. 

Scheme 39 Example of heptacyclic bis-pyrano-l,4-benzoquinone derivative...

This sequence has been successfully extended to the regioselective multicomponent construction of bis- pyrano-l,4-benzoquinone derivatives when unsubstituted 2,5-dihydroxy-l,4-benzoquinone is used (Scheme 39) [130], Depending on the alkene moiety, the reaction yielded only the linear tri-, penta-, or heptacyclic product in a 1 1 diasteromeric ratio, as illustrated with indene. 

Grosjean, E. Poinsot, J. Charrie-Duhaut, A. Tabuteau, S. Adam, P. Trendel, J. Schaeffer, J. Cotman, J. Dessort, D. Albrecht, P. (2000) A heptacyclic polyprenoid hydrocarbon in sediments a clue to unprecedented biol( cal lipids. Chan. Commun., 923-4. 

A twofold intramolecular Heck reaction of the dibromobenzene derivative 19 has been used to construct the heptacyclic skeleton 20 of cephalostatin analogs. This reaction required a precise control of the reaction time and temperature. The conversion proceeded best with a catalytic amount of the palladacycle from tris(< -tolyl)phosphine and palladium acetate, and gave exclusively (in 80% yield) the heptacycle 20 with an unusual m-annelation of the two newly formed rings (Scheme 10). ... 

Scheme 10 A twofold intramoleoular Heck reaction of a 1,4-dibromobenzene derivative leading to a heptacyclic skeleton. ...

The ultimate in the so-called zipper-mode carbopalladations has been demonstrated by Trost and Shi with the oligocyclization of the heptaenyne 130c to the heptacyclic hexaspirane... 

Acetone sensitized irradiation of the. y ,st>/-biscyc opentadienequinonc adduct 11 affords the cage compound 12 (a heptacyclic dione) in 60% yield which was further converted to 1,4-... 

A search of the literature revealed a 1982 Trost and Fortunak paper [58] wherein PdCL and AgBF4 were utilized to effect the Heck-type cyclialkylations of various isoquinuclidine model compounds. Compound 100 was exposed to these conditions, affording the heptacycle 101 in 63-82% yields. 

Closure of the seventh ring was effected by treatment of 121 with 4.68 equiv of PdC and 3.1 equiv of AgBF4 [58] in acetonitrile containing propylene oxide as an acid scavenger. The incipient heptacyclic a-pallladium adduct was worked up immediately by the addition of the ethanol and NaBHjto afford the desired indole 122. 

An example of intramolecular azide addition to the olefinic bond of an enol ether is provided by the synthesis of a heptacyclic steroidal triazoline (Scheme 63).253 The dipolar aprotic solvent that is used is considered to facilitate the cycloaddition.11 182... 

Triamantane (13) is obtained from the rearrangement of the heptacyclic dimer of cyclooctatetraene (18), after it has been elaborated to the C1S level by Simmons-Smith cyclopropanation and subsequent hydrogenolysis (Eq.(9))33l. The structure of the product, obtained in 5% yield, is again confirmed by an X-ray analysis 34>. 

Vinca minor, cultivated in Georgia, USSR, has been shown to contain ( )-vincadifformine and vincine, both already known to occur in this species, together with apovincamine and 11-methoxyvincadifformine.92 Voaphylline, voaphylline hydroxyindolenine, and 11-hydroxytabersonine have been isolated from the leaves of Tabernanthe pubescens,43/ and 5,22-dioxokopsane (177) from the root bark of Alstonia venenata R. Br. 93 this is the first report of an alkaloid of the heptacyclic kopsine group in this species. 

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