To a solution of (4) (0.25 g, 1.14 mM) and (6) (0.274 g, 1.0 mM) in dry methylene chloride (10 mL) at room temperature was added 4-dimethylaminopyridine (0.122 g, 1.0 mM) followed within one minute by a solution of N,N'-dicyclohexylcarbodiimide (0.22 g, 1.06 mM) in methylene chloride (1 mL), 3×1 mL rinses with methylene chloride. After 2 days, the filtered mixture was concentrated in vacuo and the residue flash chromatographed on silica gel using 15-20% ethyl acetate in hexane as eluant to give product 7 (0.22 g) as an oil that solidified readily in a short time.
