We have developed a useful synthetic route to a 6/5/6/5/6-oxacyclic ring system and bipentalene derivatives from dimeric 7-oxonorbornene derivatives by using ring-rearrangement metathesis as a key step. This method provides access to fused oxacycles containing eight stereogenic centers in just three steps and to bipentalene derivatives in two steps only.
21 CCDC 2175968, 2176027, and 2175972, contain the supplementary crystallographic data for compounds 10, 16, and 18. The data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures.
22Bipentalene Derivatives; General ProcedureA magnetically stirred solution of the RRM precursor in anhyd CH2Cl2 was degassed by sequential purging with N2 and ethylene gas for about 10 min each. The Grubbs catalyst was added in one portion at rt under C2H2 at 1 atm, and purging was continued for another 2–5 min. The mixture was stirred at the appropriate temperature under C2H2 until the reaction was complete (TLC). The crude product was purified by column chromatography (silica gel, EtOAc–PE).3,3′-Divinyl-2,2′,3,3′,4,4′,6a,6a′-octahydro-1,1′-bipentalene-3a,3a′(1H,1′H)-diol (12a)Colorless liquid; yield: 65%. 1H NMR (500 MHz, CDCl3): δ = 5.93–5.86 (m, 2 H), 5.69–5.68 (m, 2 H), 5.63–5.61 (m, 2 H), 5.12–5.06 (m, 4 H), 2.91–2.90 (m, 2 H), 2.69–2.65 (m, 2 H), 2.60–2.55 (m, 2 H), 2.19–2.15 (m, 2 H), 1.95–1.91 (m, 2 H), 1.85–1.81 (m, 2 H), 1.86–1.71 (m, 2 H), 1.10–1.07 (m, 2 H). 13C NMR (125 MHz, CDCl3): δ = 137.7, 130.4, 129.3, 116.1, 90.0, 60.8, 55.2, 44.5, 43.0, 34.6. HRMS (ESI, Q-ToF): m/z [M + Na]+ calcd for C20H26NaO2: 321.1825; found: 321.1823.3a,3a′-Dimethoxy-3,3′-divinyl-1,1′,2,2′,3,3′,3a,3a′,4,4′,6a,6a′-dodecahydro-1,1′-bipentalene (17)Yellow liquid; yield: 60%. 1H NMR (500 MHz, CDCl3): δ = 5.94–5.48 (m, 6 H), 5.15–5.03 (m, 4 H), 3.25 (s, 3 H), 3.20 (s, 3 H), 3.11–3.06 (m, 2 H), 2.84–2.68 (m, 2 H), 2.49–2.31 (m, 4 H), 2.19–1.88 (m, 4 H), 1.17–1.06 (m, 2 H). 13C NMR (125 MHz, CDCl3): δ = 138.5, 135.6, 133.8, 130.8, 130.3, 127.4, 117.3, 115.5, 97.9, 95.4, 54.7, 54.6, 53.9, 51.3, 51.2, 50.9, 44.6, 42.7, 38.9, 36.8, 34.5, 34.3. HRMS (ESI, Q-ToF): m/z [M + H]+ calcd for C22H31O2: 327.4800; found: 327.4805.