title: A new access to dihydrotropones through ring expansion of spirocyclohexadienones: synthesis and mechanism.
abstract: In this paper we report the rearrangement of spirocyclohexadienones into dihydrotropones in basic conditions as a new method for the preparation of seven-membered ring ketones, which are key building blocks for the synthesis of tropoloalkaloids. DFT calculations and deuterium labeling studies support the mechanism we propose for this rearrangement, involving the ring opening of a spirocyclopropane intermediate followed by successive base-catalyzed 1,3-hydrogen shifts. The X-ray structure of the resulting dihydrotropone shows near-perfect planarity and the conjugation gain is likely to be the driving force of the reaction.
authors.affiliation: Institut de Chimie des Substances Naturelles, CNRS UPR 2301, F-91198 Gif sur Yvette, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Varin
authors.forename: Angèle
authors.initials: A
authors.lastname: Chiaroni
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Lallemand
authors.forename: Bogdan
authors.initials: B
authors.lastname: Iorga
authors.forename: Catherine
authors.initials: C
authors.lastname: Guillou
mesh_terms: D003500:Cyclization; D006586:Hexanes / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D014334:Tropolone / Q000031:analogs & derivatives* / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D006586:Hexanes; D014334:Tropolone; D006859:Hydrogen; C003730:tropone