A new access to dihydrotropones through ring expansion of spirocyclohexadienones: synthesis and mechanism.
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.
Varin
Marie
M
Institut de Chimie des Substances Naturelles, CNRS UPR 2301, F-91198 Gif sur Yvette, France.
Chiaroni
Angèle
A
Lallemand
Jean-Yves
JY
Iorga
Bogdan
B
Guillou
Catherine
C
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
D006586:Hexanes; D014334:Tropolone; D006859:Hydrogen; C003730:tropone