Synthesis of an angularly fused tricycle via tandem ring closing metathesis.; Tricycles, triquinanes

Andrew Edwards (a.edwards@shef.ac.uk),
A contribution from the Harrity Group, University of Sheffield

Chemicals Used
Dichloroethane (DCE), distilled over CaH₂, Grubbs’ catalyst, Lancaster

Procedure
A solution of anti 1R*, 2, 2, 3R*-tetraallylcyclopentanediol 1 (50 mg, 0.19 mmol) was dissolved in dry, distilled DCE (2 ml). Grubbs’ catalyst [Ru(PCy₃)₂Cl₂(CHPh)] (8 mg, 0.0095 mmol) in DCE (1 ml) was added via syringe. The reaction mixture was heated to 60 ^oC under N₂ overnight. A further 5 mol% of Grubbs’ catalyst was added after 24 h. In total, 10 mol% of Grubbs catalyst had been added over 48 h with heating throughout. The solvent was removed in vacuo and purification on silica gel using 2:1 hexane:EtOAc supplied the desired tricycle 2 as a pale yellow oil. (28 mg, 72%)

Author's Comments
We have carried out many tandem ring closing metathesis reactions, and have found the catalyst to be very robust and reliable. On some of our other systems slightly higher catalyst loadings have been required to complete the conversion. The scale of the reaction does not seem to be important with 50mg reactions working as well as 1g reactions. Also, it is worth taking some care with the chromatographic purification of reactions using Ru catalysts as they have a habit of sticking to your compound. If necessary reduce the polarity of the column to overcome this problem.

Data
¹H-NMR (250 MHz, CDCl₃): d 1.60 (2H, br s, OH), 1.70-2.04 (6H, m) 2.14-2.38 (4H, m), 2.46-2.58 (2H, m), 5.54-5.71 (4H, m). ¹³C-NMR (62.9 MHz, CDCl₃): d 33.5, 35.3, 39.1, 61.3, 80.8, 125.0, 125.7.

Lead Reference
Bassindale, M.J., Edwards, A.S., Hamley, P., Adams, H., Harrity, J.P.A., Chem. Commun., 2000, 1035.

Other References
For recent metathesis reviews see: Grubbs, R.H., Chang, S., Tetrahedron, 1998, 54, 4413; Fürstner, A., Angew. Chem., Int. Ed. Engl., 2000, 39, 3012.

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