potassium tert-butylate in tetrahydrofuran; dimethyl sulfoxide (Ar); addn. of tert-BuONO to Cr-complex at room temp. with stirring; addn. of tert-BuOK (THF); addn. of tert-BuONO after 15 min; stirring for 20 min; hydrolysis with ice; E:Z = 72:28; extn. with ether; washing (H2O); drying (MgSO4); chromy. (silica gel, ether/pentane);