To a stirred solution of dimethylsulphide (7 μl, 0.1 mmol), rhodium (II) acetate (2 mg, 0.005 mmol) and N-benzylidene-toluene-p-sulphonamide (131 mg, 0.5 mmol; J. C. S. Perkin I (1981) 2435-2442) in dichloromethane (2 ml) was added phenyldiazomethane (prepared as in Example 36; 8.11 ml of a 0.074M solution in t-butylmethylether) over a period of 12 hours. Upon completion of the addition, the solvent was removed in vacuo and the residue chromatographed using silica gel eluting with 15:85 ethyl acetate:petrol to give the title compound as a 3:1 mixture of trans:cis isomers (144 mg, 82%).
