Polycyclic rearrangements. A novel,carbonium ion mediated,bicyclo (4.2.0) octa-2,4-diene→1,3,5-cyclooctatriene isomerisation in a propellane framework

A serendipitious cationic rearrangement of hexacyclic propellane $\text{9}$ to its strained fluxional isomer, the bridged 1,3,5-cyclooctatriene $\text{10}$ is described.     

Enantiospecific first total synthesis and assignment of absolute configuration of the sesquiterpene (-)-cucumin H

The first total synthesis of the sesquiterpene (-)-cucumin H, a linear triquinane isolated from Macrocystidia cucumis, has been accomplished starting from (R)-limonene employing two different cyclopentannulation methodologies, which in addition to confirming the structure also established the absolute configuration of the natural product. [reaction: see text]     

A novel, versatile synthetic approach to linearly fused tricyclopentanoids via photo-thermal olefin metathesis

Fifteen examples of a new, speedy and general approach to linearly fused tricyclopentanoids bearing the tricyclo[6.3.0.0^2,6]undecane (triquinane) frame of high contemporary interest is delineated. The key concept in our synthetic sequence to triquinanes is the novel photo-thermal olefin metathesis of cheap, abundantly available Diels-Alder adducts of 1,3 cyclopentadienes and p-benzoquinones. Thus photolysis of endo-tricyclo[6.2.1.0^2,7] undeca-4,9-dien-3,6-diones (9a–9j, 13a,b) furnished pentacyclo [5.4.0.0^2,6.0^3,10.0^5,9]undecan-8,11-diones (10a–10j, 14a,b), which on thermal fragmentation of the cyclobutane ring gave cis, syn, cis-tricyclo [6.3.0.0^2,6]undeca-4,9-dien-3,11-diones (11a–11j, 15a,b in just three steps and in exceptionally good yields. A few interesting transformations of the readily available parent bis-enone 11a which indicates its wider uses in syntheses, are described. Finally, a smooth thermal isomerisation of cis, syn, cis-bis-enones to cis, anti, cis-bis-enones is reported, which further enhances the scope and versatility of our synthetic theme.