Wickerols A and B are diterpene natural products that have a novel fused 6−5−6−6 ring framework and exhibit potent antiviral activity against the H1N1 type A influenza virus. Herein, we report a divergent synthesis of wickerols A and B in 16 and 15 steps, respectively, from commercial sitolactone. The key reactions of the synthesis are a SmI 2 -mediated intramolecular ketone−allylic acetate reductive cyclization, a Claisen rearrangement, and an intramolecular alkylation/aldol reaction that rapidly assembled the compact tetracyclic core framework in a stereocontrolled manner. The work described herein allowed us to confirm the absolute configurations of wickerols A and B.

Furans are versatile synthons in organic chemistry. Described is a general method for transforming furans into alkynes by dual C-C double-bond cleavage. The reaction is proposed to proceed by sequential [4+2] cycloaddition between furan and singlet oxygen and a formal retro-(3+2) fragmentation of the endoperoxide intermediate. A wide array of furans, including those derived from sapogenins, are amenable to this reaction, thus providing the corresponding alkynoic acids in up to 88 % yields. The synthetic utility was demonstrated by a seven-step synthesis of the proposed structure of a pregnane natural product, aglatomin B, from a known intermediate.

The development of new chemical transformations to simplify the synthesis of valuable building blocks is a challenging task in organic chemistry and has been the focus of considerable research effort. Here we report a chemical transformation that enables the facile and modular synthesis of synthetically challenging yet biologically important functionalized butenolides from easily accessible furans. Specifically, Diels–Alder reactions between furans and singlet oxygen generate versatile hydroperoxide intermediates, which undergo iron(II)‐mediated radical fragmentation in the presence of Cu(OAc)2 or various radical trapping reagents to afford butenolides bearing a wide variety of appended remote functional groups, including olefins, halides, azides, and aldehydes. The practical utility of this transformation is demonstrated by easy diversification of the products by means of cross‐coupling reactions and, most importantly, by its ability to simplify the syntheses of known building blocks of eight biologically active natural products.