ammonium chloride in hexane; benzene soln. of NH4Cl in benzene cooled in ice bath, slowly addn. of Al(CH3)3 in hexane, cloudy soln. stirred in ice bath for 30 min, at room temp. for 2 h, soln. transferred to flask with soln. of tin ester, soln. heated at 60°C overnight; diluted with CHCl3, organic layer washed with water, dried over MgSO4, filtrn., evapn. in vac. left brown residue, purified by column chromy.; elem. anal.;