En Route to Furan-Fused Naphthopyrones: Formal Synthesis of the (+)-Lasionectrin and Its C12-Epimer.

Despite the vast presence of the furan-fused naphthopyrone (FFN) skeleton in many bioactive natural products, such as lasionectrin, at present, a general approach to FFNs has not been developed yet. For that reason, a simple and straightforward synthetic approach consisting of a sequential procedure of a Diels-Alder reaction between 1,3-dimethoxy-benzocyclobutenol I and furan-fused-α,ß-unsaturated-δ-lactones II (via an ο-quinodimethane intermediate III) followed by an oxidative aromatization of the corresponding Diels-Alder adduct IV is reported. Subsequently, the formal synthesis of the (+)-lasionectrin and its C12-epimer was achieved, the latter in only six steps.

Electrochemical Corey-Winter reaction. Reduction of thiocarbonates in aqueous methanol media and application to the synthesis of a naturally occurring α-pyrone.

An electrochemical version of the Corey-Winter reaction was developed giving excellent results in aqueous methanol media (MeOH/H2O (80:20) with AcOH/AcONa buffer 0.5 M as supporting electrolyte), using a reticulated vitreous carbon as cathode in a divided cell. The electrochemical version is much more environmentally friendly than the classical reaction, where a large excess of trialkyl phosphite as reducing agent and high temperatures are required. Thus, cathodic reduction at room temperature of two cyclic thiocarbonates (-1.2 to -1.4 V vs Ag/AgCl) afforded the corresponding alkenes, trans-6-(pent-1-enyl)-α-pyrone and trans-6-(pent-1,4-dienyl)-α-pyrone, which are naturally occurring metabolites isolated from Trichoderma viride and Penicillium, in high chemical yield and with excellent stereo selectivity.