The structural identity of pethybrene was confirmed as theoretically proposed 6-5-5 tricyclic structure through total syntheses of two putative structures. The originally proposed structure 1 was synthesized in 13 steps via Intramolecular Pauson-Khand reaction to form the triquinane skeleton and the newly proposed structure from a theoretical study 2 was obtained from a known [2 + 2] cycloaddition product in 3 steps.
We
describe a method to generate alkylidene carbenes via tetramethylammonium-fluoride-induced
desilylation of silyl vinyl iodides. The reversible carbene generation
from an iodovinyl anion enabled us to unearth mechanistic aspects
of the trimethylenemethane (TMM) diyl cyclization reaction that could
not be explored via previous methods. We observed that a slow diyl–diylophile
cycloaddition can induce the reversible formation of an alkylidene
carbene from the TMM diyl intermediate via a retro-cyclopropanation
at ambient temperature.
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