Triphenylphosphine → [(3-Nitrophenyl)methyl](triphenyl)phosphanium bromide

Participants

Reaction Steps

A suspension of 3-nitrobenzyl bromide (10 g, 46 mmol) in acetonltrile (100 ml) was added to a solution of triphenylphosphine (13.3 g, 51 mmol) in acetonitrile (150 ml). The resulting suspension was heated at reflux (15 min), cooled and 15.5 g of (3-nitrobenzyl)triphenylphosphonium bromide was obtained by filtration. A mixture of this compound (10 g, 21 mmol) and imidazole-2-carboxaldehyde (2 g, 21 mmol) was heated at reflux in ethanol (200 ml) and a solution of sodium ethoxide in ethanol (sodium (480 mg, 21 mmol; ethanol (100 ml)) was added dropwise over 2 h. After a further 3 h at reflux the solution was cooled, filtered and the solvent evaporated. The residue was taken up in 2M HCl (50 ml). The aqueous phase was washed with diethyl ether (3×50 ml), basified with 1N sodium hydroxide solution and the product extracted into diethyl ether (3×50 ml). The organic phase was dried (NaSO4) and evaporated to afford 4 g of a crude cis/trans mixture of 2-((3-nitrophenyl)ethen-2-yl)imidazole as a yellow solid. This material (1.75 g, 8.14 mmol) was dissolved in a mixture of dichloromethane (40 ml) and acetonitrile (40 ml) and di-t-butyl dicarbonate (2.13 g, 9.8 mmol) was added. After 48 h at room temperature the solvent was evaporated and the residue chromatographed on silica gel with ethyl acetate:petrol (bp 60°-80°) (1:1) as eluant to afford 1.7 g of a cis/trans mixture of the titled compound as a yellow oil. 1H NMR (250 MHz, CDCl3) δ 1.64 and 1.70 (9H, 2s), 6.72-8.50 (8H).

Provenance & Evidence