6,7‐Benzotropolone Syntheses Based on Ring‐Closing Metatheses and Four‐Electron Oxidations
作者:Michael Kreibich、Manuel Gemander、David Peter、Dharmendra B. Yadav、Charles B. de Koning、Manuel A. Fernandes、Ivan R. Green、Willem A. L. van Otterlo、Reinhard Brückner
DOI:10.1002/ejoc.202000256
日期:2020.5.22
Homoallyl ortho‐vinylaryl ketones were prepared through several different routes. In the presence of 1–2 mol‐% Grubbs‐II catalyst, these substrates cyclized to give 6,7‐dihydrobenzocyclohepten‐5‐ones. The enolates derived therefrom by treatment with NaHMDS in THF were oxidized by a stream of molecular oxygen at 0 °C. This furnished 6‐hydroxybenzocyclohepten‐5‐ones (“6,7‐benzotropolones”).
DEWAR1 has interpreted the chemistry of the mould metabolite, stipitatic acid, and of colchiceine (the methyl ether of which is the alkaloid colchicine) by postulating that they are derived from the hypothetical cycloheptatrienolone (I). This he termed 'tropolone', and he attributed to it quasi-aromatic character. This interesting suggestion, for which no tangible evidence was advanced2, has acquired more plausibility from the recent demonstration of Haworth, Moore and Pauson3 that purpurogallin is a trihydroxybenztropolone, as earlier suggested by Barltrop and Nicholson4, and from the finding of Erdtman and Gripenberg5 that the cedar-wood constituent γ-thujaplicin is an isopropyltropolone. Hitherto, a synthetic tropolone of established constitution has not been prepared, and the properties ascribed to such a structure have been based largely on speculation.
Syntheses of 3,4-Benzotropolones by Ring-Closing Metatheses
作者:Deniz Arican、Reinhard Brückner
DOI:10.1021/ol400510j
日期:2013.6.7
Ortho-lithiated styrenes or ortho-lithiated benzaldehyde dimethylacetals were added to 2,2-dimethoxypent-4-enals 7. The resulting alcohols were carried on to the aromatic dienones 10. These were ring-closed by olefin metathesis. Hydrolysis of the dimethylketal moiety and enolization provided the 3,4-benzotropolones 5. Overall, this access comprises 4–6 steps and totaled a 22–81% yield.
Chemistry of the Benzotropone Endoperoxides and Their Conversion into Tropolone Derivatives: Unusual Endoperoxide Rearrangements
作者:Murat Güney、Arif Daştan、Metin Balci
DOI:10.1002/hlca.200590061
日期:2005.4
The chemistry of two bicyclicendoperoxides, obtained by photooxygenation of 2,3-benzotropone (=5H-benzocyclohepten-5-one; 5) and of its ethyl carboxylate derivative 15, was investigated with the aim of synthesizing the respective benzotropolone derivatives. The reaction of the endoperoxide 10 derived from 5 with thiourea gave the desired benzotropolone, i.e., 6-hydroxy-5H-benzocyclohepten-5-one (11)