Heptacyclic ring system

Shoreaketone (742) from the stem bark of Shorea uliginosa (Dipterocarpaceae) has a novel framework of fused heptacyclic ring system including an a,y9-unsaturated carbonyl group. Shoreaketone (742) exists as rotational isomers [210]. 

In our retrosynthetic analysis of communesin F (Scheme 10), we envisioned constructing the upper hemisphere of the heptacyclic ring system of the target... 

Daphlongeranines B and A possess a unique heptacyclic ring system with one or two laetones, respeetively. 

A new alkaloid, stryvomicine A, that contains an unprecedented heptacyclic ring system, was isolated from the seeds of Strychnos nux-vomica (14TL6538). Octahydropyrrolo[2,l-l)][l,3]ox(thi)azepines were found to potendy sensitize previously resistant cancer cell lines to TNF-related apoptosis-inducing ligand (14MCT5). 

Benzo[l,2-c 3,4-c 5,6-c ]tris[l,2,5]thiadiazole.—Four related condensed tetracyclic ring systems incorporating 1,2,5-thiadiazole (202 X = S, Se, CH, or CH=CH) are accessible from a common starting material, benzo[l,2-c 3,4-c ]-bis[l,2,5]thiadiazole (200), which is converted into the diamine (201) and variously cyclized to (202). The condensation of (201) and 9,10-phenanthrene-quinone in boiling acetic acid similarly yields the heptacyclic ring system dibenzo-[a,c]bis[l,2,5]thiadiazolo[3,4-/r.3, 4V]phenazine. 2... 

The useful synthetic utilities of photosensitized oxidation of furans were demonstrated. A notable example was the oxidation of the trisubstituted furan 29 shown in Scheme 16 to the (Z)-7-keto-o,/ -unsaturated ester intermediate 30, a crucial step for the construction of the ABC ring system of the complex heptacyclic marine alkaloid norzoanthamine <2004SCI495>. 

Schemes 2.3a-c outline the retro-synthetic production of BTX B (1). The final approach to PbTx-2 involved separate assembly of the ABCDEFG and UK ring systems 4 and 5, their coupling, and final elaboration to the end. The didehydrooxocane ring in BTX B (ring H) was thus designated as the final ring to be constructed. Retro-synthetic cleavage of the indicated C-0 bond in 1 and removal of the terminal electrophilic groupings reveal hydroxy dithioketal 3 as a plausible precursor. Tricyclic aldehyde 4 and heptacyclic phosphonium salt 5 can thus be defined as potential precursors to 3. The reliable and usually stereoselective Wittig reaction would be employed to accomplish the union of compounds 4 and 5 (Scheme 2.3a). Tricyclic aldehyde 4 was traced retro-synthetically to D-mannose 10.

This ring system can be seen in the pentacyclic alkaloids ascididemin 28, 2-bromoleptoclinidone 29, 11-hydroxyascididemin 30, 8,9-dihydro-ll-hydroxyascididemin 31, calliactine 32, the heptacyclic eilatin 33, and the octacyclic biemnadin 34. (See Section II,D,1 on pyrido[2,3,4-/c/]acridines.)... 

Figure 2 Heptacyclic von Baeyer ring system and its name together with the numbering of atoms...

Pattenden has described the reduction of a triene selenyl ester, RCOSeR, by a cascade sequence to give a tetracyclic steroidal ketone,157 and of an acyclic heptaene selenyl ester, by a seven-fold cascade of ring closures to give a heptacyclic system.158... 

The cycloaddition/rearrangement IMDAF cascade of 2-amidofurans such as 319 was remarkably efficient given that two heteroaromatic systems are compromised in the reaction. Closure of 321 to the remaining D-ring of the Strychnos skeleton (i.e., 322) was carried out from the aza-tetracyclic intermediate 321 by an intramolecular palladium-catalyzed enolate-driven cross-coupling between the A-tethered vinyl iodide and the keto functionality. The cycloaddition/rearrangement approach was successfully applied to a synthesis of the heptacyclic fi-amework of ( )-strychnine 323 (Scheme 13.72) [114], which required only 13 steps from furanyl indole 319 and proceeded in an overall yield of 4.4%. 

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