4443-89-4Relevant academic research and scientific papers
6,7-Benzotropolone Syntheses Based on Ring-Closing Metatheses and Four-Electron Oxidations
Brückner, Reinhard,Fernandes, Manuel A.,Gemander, Manuel,Green, Ivan R.,Kreibich, Michael,Peter, David,Yadav, Dharmendra B.,de Koning, Charles B.,van Otterlo, Willem A. L.
, (2020)
Four homoallyl ortho-vinylaryl ketones (10a-d) – 1,8-dienes of sorts – were prepared by several approaches. In the presence of 1–2 mol-% Grubbs-II catalyst, they ring-closed to give 6,7-dihydrobenzocyclohepten-5-ones (11a-d) in 90–96 % yield. With SeO2 the parent compound (11a) delivered benzocyclohepten-5-one (13a) and/or selenium-containing compounds (18–22) but no more than traces of 6,7-benzotropolone (5a). However, 5a was accessible from compound 11a via the sodium enolate and allowing it to react with a stream of oxygen (43 % yield). The sodium enolates of the substituted 6,7-dihydrobenzocyclohepten-5-ones 11b–d and oxygen underwent analogous 4-electron oxidations. This furnished the substituted 6,7-benzotropolones 11b-d. In contrast, the corresponding lithium enolates were inert towards oxygen. The 6,7-dihydrobenzocyclohepten-5-one 11d was also accessed differently, namely by a Grubbs-II catalyst-mediated RCM/C=C migration tandem reaction of the allyl ortho-allylaryl ketone 73 – another 1,8-diene of sorts (90 % yield).
