Cyclopentane, electrophilic oxygenation

Baran also postulated that these simpler dimeric PIAs could be precursors to the more advanced tetracyclic and hexacyclic family members. Key to this hypothesis was the common putative intermediate pre-axinellamine (139), which hypothetically could be produced from both the rearrangement of sceptrin (66) or ageliferin (132) (Schane 13.22) [114]. Oxidative ring expansion (sceptrin) or contraction (ageliferin) induced by either electrophilic oxygen or chlorine, respectively, would lead to formation of the highly functionalized cyclopentane core (137) of this hypothetical compound. Eurther oxidation of the aminoimidazole would then yield pre-axinellamine (139). 

A condensation of vinyl sulphides of synthetic value involves the reaction of a-ethylthio-styrenes with an aldehyde in the presence of a Lewis acid catalyst to give 3-ethylthio-indenes. Regiospecific and stereospecific pentannelation i.e, fusion of a cyclopentane ring) of an alicyclic ketone involves arylthiomethylen-ation followed by base-catalysed addition to an aj8-unsaturated ester. a-Phenyl-thiobutenolides are less reactive Michael acceptors than their sulphoxide counterparts, and /SjS-dichlorovinyl sulphides are less reactive in electrophilic reactions than their oxygen counterparts. Dimerization of aryl a-cyanovinyl sulphides occurs more readily than that of alkyl analogues, since the intermediate 1,4-diradical ArSC(CN)CH2CH2d(CN)SAr, which cyclizes to the cyclobutane, is more stable. Products obtained by photolysis of methyl vinyl sulphide are accounted for by homolysis of both vinyl—S and methyl—S bonds. The kinetics of catalysed cis-trans isomerization of aryl vinyl sulphides have been studied. ... 

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