The new synthesis of sesquiterpenoids 10-bromo-α-chamigrene

The new synthesis of 10-bromo-α-chamigrene was achieved as follows; 6-methyl-5-heptene-2-one was transformed into corresponding thioacetals,and then successively treated with Cp2Ti(P(OEt)3)2.The intermediate reacted with mono-ketal of cyclohexane-1,4-dione,and gave the carbonyl coupling product.It was then transformed into the key intermediate γ-bisabolene via deketalization,Grignard reaction,dehydration and then furnished the target molecule by polyene cyclization,with total yield 2%.All structures were confirmed by 1H NMR and 13C NMR.The final compound was confirmed by 1H NMR,13C NMR and MS.