Superacid-Catalyzed Cyclization of Methyl (6Z)-Geranylfarnesoates

Methyl (2Z,6Z,10E,14E)- (3) and methyl (2E,6Z,10E,14E)-geranylfarnesoate (4) were prepared, and then individually cyclized in the presence of the superacid FSO3H. In the case of substrate 3, the scalaranic ester 9 (26%) and the cheilanthanic ester 10 (39%) were isolated. Under the same conditions, substrate 4 afforded a mixture of the corresponding stereoisomers 11 (25%) and 12 (63%). The observed product selectivity supports that the internal, (6Z)-configured CC bond in these and other biologically relevant substrates plays an essential role in the cyclization process.