The total number of stereo isomers =2² for non-plane of symmetric compounds. The α- onocerin will have 256 stereo isomers.
Method of synthesis :_
The conversion of carbonyl group to hexocyclic methylene group should be carried out. The best method for this is wittig reaction, but witting reaction doesn't takes place in the case reason, but may be the steric effect of the dicyclic compound,
The dione is the starting material one of the keto group using ethylene glycol. The other keto group is reacted with phosphorus ylide wittig reaction and alkene is formed. The resulting compound is treated with osmium. Tetraoxide and 1,2 diol is formed, to direct the rearrangement of the diol(pinaclo-pinaclone) rearrangement. It's necessary to facilitate tertiary allylic alcohols, Tosylation of the diol is used. It generate the secondary tosylate and then the rearrangement was carried out in a ionizing and non- acidic medium. The migration of the vinyl group in preference to the saturated carbon cahin takes place to give the ketone-ketal is fourth converted to fifth by treating with HCl which undergoes deprotection of keto group followed by isomerisation.
The enediol fourth is converted seventh the bridged dion in 10-20% yield, in the presence of strong base, the enediol is degraded in presence of weak base undergo intramolecular, Michel type addition and give the basic carbon framework of longifelon. The methylation is carried out in the tricyclic ketone fourth. After the protection of keto group as thio-ketal to form eighth, then deprotection takes place by treating with LiAlH4, N2H4KOH and CrO3, CH3COOH to form nineth. The compound nineth is treated with CH3Li base and SOCI2 to form longifelon.
Very informative
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