Putative biomimetic route to 8-oxabicyclo[3.2.1]octane motif from a humulene sesquiterpenoid zerumbone
Kollery S. Veena, Greeshma Gopalan, Murali Madhukrishnan, Sunil Varughese, Kokkuvayil Vasu Radhakrishnan* and Ravi Shankar Lankalapalli*
An approach to expand the diversity of terpenes to novel polycyclic skeletons with contiguous stereogenic centers is described. An unprecedented 8-oxabicyclo[3.2.1]octane motif was obtained in quantitative yield by photoirradiation of zerumbone in the presence of a catalytic amount of Lewis acid. The vital role of light in the isomerization of double bonds in zerumbone, which ensued cyclization via tertiary carbocation intermediate, emulates a biosynthetic route. Synthetic diversification of the phototransformed product afforded epoxy derivatives with up to seven contiguous stereogenic centers and eight-member ring fused tricyclic motifs. The present work sheds light on the possible role of UV irradiation in the biosynthesis of oxo-bridged tricyclic structures from polyene terpenes.
Organic Letters 2020, 22, 6409-6413. DOI: 10.1021/acs.orglett.0c02220.