Gold-catalyzed stereoselective cycloisomerization of allenoic acids for two types of common natural γ-butyrolactones.

γ-(E)-Vinylic and γ-alkylic γ-butyrolactones are two different types of lactones existing extensively in animals and plants and many of them show interesting biological activities. Nature makes alkylic γ-butyrolactones by many different enzymatic lactonization processes. Scientists have been mimicking the natural strategy by developing new catalysts. However, direct and efficient access to γ-(E)-vinylic γ-butyrolactones is still extremely limited. Here, we wish to present our modular allene approach, which provides an efficient asymmetric approach to (E)-vinylic γ-butyrolactones from allenoic acids by identifying a new gold complex as the catalyst. Based on this cycloisomerization strategy, the first syntheses of racemic xestospongiene and xestospongienes E, F, G, and H have been realized and the absolute configurations of the chiral centers in xestospongienes E and F have been revised. In addition, by applying a C-O bond cleavage-free hydrogenation, the syntheses of naturally occurring γ-alkylic γ-lactones, (R)-4-tetradecalactone, (S)-4-tetradecalactone, (R)-γ-palmitolactone, and (R)-4-decalactone, have also been achieved.