First Enantioselective Synthesis of Marine Diterpene Ambliol‐A

The first enantioselective synthesis of furanditerpene ambliol‐A, which is a major metabolite of marine sponge Dysidea amblia , has been accomplished by starting from racemic α‐ionone. The key steps of the synthesis include lipase‐mediated resolution of 4‐hydroxy‐γ‐ionone, its stereoselective transformation into trans ‐α‐epoxy‐dihydroionone, C 2 homologation to trans ‐α‐epoxy‐monocyclofarnesyl acetate and Li 2 CuCl 4 ‐catalysed sp 3 –sp 3 cross‐coupling reaction of the latter ester with (furan‐3‐ylmethyl)magnesium chloride. This work confirms the chemical structure previously assigned to ambliol‐A and proves that the natural levorotatory isomer does not possess (1 S ,2 S ) absolute configuration, as previously indicated, but is the opposite enantiomer, (1 R ,2 R )‐2‐[( E )‐6‐(furan‐3‐yl)‐3‐methylhex‐3‐enyl]‐1,3,3‐trimethylcyclohexanol.