LiC(CH3)3 in n-heptane (C6H5)3SnCl in heptane was treated with LiC(CH3)3 in pentane at 0 .degre.C, then stirring at 25 °C for 12 h;;

1,2,4,5-benzenetetracarboxylic acid tetramethyl ester in acetonitrile 100 h; Irradiation;