
%0 Journal Article
%A Frey, Barbara 
%A Wells, Adam P. 
%A Roden, Frances 
%A Au, Ty Duong 
%A Hockless, David C. 
%A Willis, Anthony C. 
%A Mander, Lewis N. 
%T Total Synthesis of the Pentacyclic Diterpenoid Tropone Hainanolidol
%J Australian Journal of Chemistry
%D 2001/04/05
%V 53
%N 10
%P 819-830
%K Hainanolidol; diterpenoids; Yew bark; tropones; harringtonolide.
%R https://doi.org/10.1071/CH00124
%U https://www.publish.csiro.au/paper/CH00124 
%X The total synthesis of the unusual diterpenoid tropone, hainanolidol (1), discovered in the bark of the yew species, Cephalotaxus hainanensis, has been completed in 26 steps from 3,5-dimethylanisole. The intramolecular cyclopropanation reaction of the aryl ring in (30) by means of the rhodium mandelate-catalysed reaction of the diazoacetyl function was used to assemble the 5/7 ring system of (31), at the same time elaborating a cycloheptatriene moiety that could be transformed subsequently to the tropone functionality in the target molecule. While removing the acetal protecting group from (31) an unexpected Mukaiyama&#8211;type aldol process was induced by ZnBr2, affording (32), the structure of which was determined by X-ray analysis. With greater care, the aldehyde (33) could be obtained and the desired carbocyclic ring system completed by means of a base-catalysed aldol reaction with the newly formed hydroxyl being employed subsequently in the formation of the &#963;-lactone function in (35). Desilylation, reduction of the C-10 carbonyl function and brief exposure to acid finally afforded (1). This last step took advantage of the stability of the tropylium ion (40) to provide a &#8216;thermodynamic sink&#8217; for the reaction outcome. The synthesis of (1) also constitutes a formal synthesis of the troponoid ether, harringtonolide (2), since this compound had been obtained previously from (1) by means of a transannular oxidation process. Methodology for the assembly of the tropone moiety in (1) and (2) was modelled on the simpler bi- and tricyclic systems, (13) and (22), respectively. 
