Sinularene

A stereoselective synthesis of sinularene (8) and the 5-epimer (9) from a norbornene also involves as the key step the Mg-ene reaction 6—>7, The product can be converted by known reactions into either 8 or 9.5... 

Silver(I) acetate, 396 Silver hexafluoroantimonate, 467 Silver imidazolate, 467 Silver nitrite-Mercury(II) chloride, 467-468 Silver(l) oxide, 468-469 Silver(II) oxide, 469 Silver perchlorate, 469-470 Silver tetrafluoroborate, 471 Silver(I) trifluoracetate, 471 Simmons-Smith reagent, 210-211, 472, 598 Sinularene, 246 Slaframine, 114, 115 Sodium amalgam, 473-475 Sodium-Ammonia, 472 Sodium benzeneselenoate, 475 Sodium bicarbonate, 476 Sodium bis(methoxyethoxy)aluminum hydride, 93, 476-477 Sodium borate, 322 Sodium borohydride, 477-479, 499 Sodium borohydride-Cobalt(IF) chloride, 479 Sodium borohydride-Methanesulfonic acid,... 

Catalytic hydrogenation will usually open the less hindered bond adjacent to the carbonyl-substituted cyclopropane carbon Therefore, construction of the sinularene skeleton has become possible (cleavage of bond a) on the other hand, Cr(II) breaks the more shielded C-C bond (cleavage of bond b) in a very similar compound yielding the longifolene system (equation 34) . 

The bicyclic cyclopropyl ketone shown in equation 174—easily accessible from the corresponding diazocarbonyl compound—could be transformed into two bicyclic divinylcyclopropanes with different functionality and positioning of the cyclopentene double bond. Rearrangement of these compounds leads to the bicyclo[12.1]octane series Very recent syntheses of the terpenes sinularene and quadrone include a pivotal Cope process of divinylcyclopropanes generated and rearranged in an analogous fashion (equation 175) . 

Substituted tetracyclo[5.4.0.0 . 0 ]undec-10-en-5-ones, e.g. 27, which can be made by intramolecular Diels-Alder cycloaddition reactions, offer potential synthetic entries to sinularene-type 28 and longifolene-type 29 natural products via reductive cleavage. ... 

For other 6-substituted derivatives, the proportions of the two products were reversed when zinc(II) chloride in methanol, or chromium(II) sulfate in aqueous dimethylformamide, was used as reductant. Lithium/ammonia reduction of ethyl 5-oxotetracyclo[5.4.0.0 . 0 ]un-dec-lO-ene-8-carboxylate (30) gave a higher proportion of the sinularene-type product, ethyl 2-methyl-4-oxotricyclo[4.4.0.0 ]decane-7-carboxylate (31), than the longifolene-type, ethyl 5-oxotricyclo[5.4.0.0 ]undecane-8-carboxylate (32). Once again, these proportions were reversed for other 8-substituted substrates when zinc metal/zinc(II) chloride in methanol, or chromium(II) sulfate in aqueous dimethylformamide, was used to induce cyclopropane cleavage. ... 

Several sesquiterpenes have been synthesized using this methodology. Bicyclo[3.2.1]octadiene 92, obtained in excellent yield from 91, has been used in the synthesis of prezizaene (93). Other targets included sinularene (94) and quadrone (95). ... 

C12 hydrocarbon (271)135 by a similar route but this compound is not identical to a tricyclic hydrocarbon isolated from East Indian sandalwood oil and reported to have this structure. (+)-Copacamphor (272) and (+)-copaborneol (273) have been isolated from Espeltiopsis guacharaca.136 The interesting sinularene derivative (274) and the acetoxycyclosinularane (275) have been isolated from the marine source, Clavularia inflata.137 These compounds, together with an aromadendrane derivative (see p. 181) are the first sesquiterpenoids from Octocorallia of the order Stolonifera. 

---