We present in this report the development of a convergent and highly stereocontrolled cycloaddition strategy toward the synthesis of C-1, C-6, and C-14 tris-oxygenated eudesmane sesquiterpenoids. This approach was demonstrated in the first total synthesis of (±)-6β,14-epoxyeudesm-4(15)-en-1β-ol (1), a structurally unique ethereal eudesmane sesquiterpenoid, via an effective Diels–Alder construction of a compact functionalized tricycle intermediate from readily available N-benzylfurfurylamine (2) and homoprenyl maleic anhydride (3) as the C5 and C10 building blocks, respectively.

A concise total synthesis of (±)-cephalotaxine (1) has been achieved from dioxolanone derivative 15 via a transannulation strategy. The key transformation is a facile reductive oxy-Nazarov cyclization as illustrated above, involving presumably a tethered 1,2-oxidopentadienyl cation species 7a or 7b, which represents a new variant of the oxy-Nazarov cyclization and constitutes an effective, regio- and stereospecific 5-hydroxy cyclopentenone annulation protocol under mild hydride reduction conditions.

We present in this report the development and realization of a novel formal total synthesis of estrone (1) via the Torgov diene (24) by the furano diene approach, first attempted by Woodward in 1937. The core ring structure 16 was established by an acid-mediated regioselective and stereospecific cyclization of the endo-oxabicyclo[2.2.1]heptene derivative 14, which is readily available from the AlCl3-catalyzed Diels−Alder cycloaddition of 2-(3-methoxyphenethyl)furan (4) and dimethyl maleate. The mechanistic pathway of this SN′ type cyclization is discussed, and the earlier perspectives in our preliminary report (Org. Lett. 2004, 6, 1333) are corrected.