Isoagathic acid

The cyclization of agathic acid by formic acid to afford the tricyclic isoagathic acid has been known for many years. The stereochemistry of the comparable cyclization products (15) and (16) of methyl jE-anticopalate (13) and methyl Z-anticopalate (14)... 

The acid-catalysed cyclization of labdanes has continued to attract attention. The influence of a C-15 carbonyl group, as in (15), leads to compounds of the pimarane series (16) and to the enol-ether (17) rather than isoagathic acid derivatives even in the presence of formic acid. The tetracyclic alcohol (20) has been obtained by dehydration of sclareol (18) with perchloric acid. It is presumably formed via the carbocation (19). 

The new diterpene, named isoagatholactone, proved to be the first naturally occurring compound with the carbon skeleton of isoagathic acid, the acid-catalyzed cyclization product of agathic acid (30, 159). Structure (63) for isoagatholactone without sterical implications was suggested... 

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