Functionalized Chromans from ortho-Quinone Methides and Arylallenes

Abstract

ortho-Quinone methides (o-QMs) underwent formal [4 + 2]-cycloaddition reactions with arylallenes regioselectively at the styrenyl olefin to furnish the corresponding 3-methylene-2-arylchromans in moderate to good yields (up to 88%). When R ≠ H, the reactions also proceeded with moderate stereoselectivity (up to 5:1) which was governed by the nature of the R group. The 3-methylene-2-arylchromans could serve as common intermediates for further functionalization including epoxidation, oxidative cleavage/Baeyer–Villiger oxidation, Riley oxidation, acid-catalyzed rearrangement, and Pd-catalyzed cross-coupling reactions to furnish the corresponding derivatives in moderate to good yields.

Total Synthesis of (±)-Rubriflordilactone A

“…With ample quantities of both indanone 6 and ( E )- 20c in hand, we were ready to explore the key intermolecular o -QM type [4 + 2]-cycloaddition. Although such reaction is a powerful tool for biosynthesis chromans, its applications to the total synthesis of natural products remain rather scarce. , It was quite discouraging to our investigation that assembly of the F-ring of rubriflordilactone A ( 3 ) via an endo - o -QM type [4 + 2]-cycloaddition by Ploypradith carried an incorrect configuration . Since it has been reported that the endo-/exo-selectivity in the intermolecular Diels–Alder reaction can be modulated by adding an appropriate catalyst to the system or attaching a suitable substituent in the substrate, we envisioned that construction of the F-ring with desired stereocontrol should be achievable via an o -QM type [4 + 2]-cycloaddition approach.…”