Asymmetric phenylation of 2,3-dihydrofuran

A solution of phenyl trifluoromethanesulfonate (30.0 mg, 0.13 mmol) and n-tridecane (10.0 mg, 0.054 mmol) in either toluene (0.5 mL) or benzene (0.5 mL) was added to a 5-mL Schlenk tube containing Pd2(dba)3 (2.3 mg, 0.004 mmol) and 1 -[4-(5)-terf-butyl-2-oxazolin-2-yl]-2-(5)-(diphenylphosphino)ferrocene (3.96 mg, 0.008 mmol) under an atmosphere of nitrogen. To this was added 2,3-dihydrofuran (46.2 mg, 0.65 mmol) and base (0.39 mmol) (Table 5.5). The resulting solution was degassed by three freeze-thaw cycles at 0.01 mbar and left to stir under nitrogen at 80 °C for 14 days giving a red solution with precipitation of Base.HOTf. 

A normal sized TLC plate was run and a strip cut off and visualised with KMnCV The silica of the remainder of the plate at the same Rf as the product was then scraped off and extracted with dichloromethane to give 2-phenyl-2,5-dihydrofuran. The enantiomeric excess was determined by chiral GC, (y-CD-TFA, 30 m, 80-90 °C, 0.3 °C min-1, 90-120 °C, 5 °C min-1, 10 minutes, 15 psi, injector temperature 200 °C, detector temperature 220 °C). 

METAL CATALYSED CARBON-CARBON BOND-FORMING REACTIONS 

The procedure to prepare the ligand is very easy to reproduce. The asymmetric intermolecular phenylation of 2,3-dihydrofuran proceeds in moderate to good yields and with excellent enantioselectivities. The solvent and base employed were varied in an attempt to optimise the reaction, Table 5.5. 

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Table 5.5 Asymmetric phenylation of 2,3-dihydrofuran using palladium complexes of l-[4-(5)-tert-butyl-2-oxazolin-2-yl]-2-(5)-(diphenylphosphino) ferrocene as catalyst.

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