A solution of dimethyl sulfoxide (2,04 ml, 28.8 mmol, 2.4 equiv) in 6.0 ml of dichloromethane is added dropwise within 5 min to a stirred solution of oxalyl chloride (1.14 ml, 13.2 mmol, 1.1 equiv) in 30 ml of dichloromethane cooled to −78° C. The mixture is stirred for 10 min at −70° C. A solution of (S,4E)-3-(tert-butyldimethylsilyloxy)-1-hydroxy-4-methyl-5-(2-methylthiazol-4-yl)-pent-4-ene 16 (3.93 g, 12.0 mmol) in 5 ml of dichloromethane is added dropwise within 5 min. The mixture is stirred for 30 min at −70° C. The reaction is quenched by dropwise addition of triethyl amine (8.4 ml, 60.0 mmol). The mixture is warmed to r.t. within 45 min. Water (30 ml) is added and the mixture is stirred for 10 min. The organic layer is seperated and the aqueous layer is extracted with dichloromethane (3×100 ml). The combined organic extracts are dried over magnesium sulfate and concentrated in vacuo. Purification of the residue by flash column chromatography (pentane/diethyl ether 5:2) affords (S,4E)-3-(tert-butyadimethylsilyloxy)-4-methyl-5-(2-methylthiazol-4-yl)-pent-4en-1-al 17 (3.21 g, 82%) as a pale yellow oil.
