A tandem olefin metathesis/oxidative cyclization has been developed to synthesize 2,5-disubstituted tetrahydrofuran (THF) diols in a stereocontrolled fashion from simple olefin precursors. The ruthenium metathesis catalyst is converted into an oxidation catalyst in the second step and is thus responsible for both catalytic steps. The stereochemistry of the 1,5-diene intermediate can be controlled through the choice of catalyst and the type of metathesis conducted. This olefin stereochemistry then controls the THF diol stereochemistry through a highly stereospecific oxidative cyclization.

Materials and Methods. Unless stated otherwise, reactions were conducted in oven-dried glassware under an atmosphere of nitrogen using anhydrous solvents. THF was obtained from an Aldrich Sureseal bottle. Tetrabutylammonium difluorotriphenylsilicate was obtained from Aldrich. The following reagents and solvents were distilled prior to use: chlorotrimethylsilane (TMSCl), trimethylsilyl trifluoromethanesulfonate (TMSOTf), tetramethylenediamine (TMEDA), and heptane. Analytical thin-layer chromatography (TLC) was performed on precoated, glass-backed silica gel (Merck 60 F 254 ). Flash column chromatography was performed using an automated purification system (Teledyne Isco Combiflash® Rf). Pre-packed normal phase silica gel column was used for separation of products using Teledyne Isco RediSep® Rf High Performance Gold column. Microwave experiments were conducted with a Biotage® Initiator+ Microwave System equipped with a Robot Sixty sample changer. High resolution mass spectroscopy (HRMS) was performed on a Thermo Scientific LTQ Orbitrap Discovery instrument coupled with ESI. Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker 400 MHz or 500 MHz spectrometer. Chemical shifts for 1 H NMR spectra are recorded in parts per million with the solvent resonance as the internal standard CHCl 3 (δ = 7.26 ppm) or DMSO (δ = 2.50 ppm). Data are reported as follows: chemical

Although the parent 2-pyrone is known to react with simple o-benzynes to produce naphthalene derivatives, there appear to be no examples of the successful reaction of coumarin, a benzo-annulated 2-pyrone analogue, with an aryne. We report such a process here using benzynes generated by the hexadehydro-Diels–Alder reaction to produce phenanthrene derivatives (i.e., benzo-annulated naphthalenes). Density functional theory computations were used to help understand the difference in reactivity between 2-pyrone and the slower trapping agent, coumarin. Finally, the reaction of o-benzyne itself [from o-(trimethylsilyl)­phenyl triflate and CsF] with coumarin was shown to be viable, although slow.