triethylamine in tetrahydrofuran under N2, dione in THF added dropwise to stirred soln. SbCl3/THF at -78°C, triethylamine/THF added dropwise to cold mixt. (0.5h), mixt. stirred at -78°C for 1h, then allowed to warm to room temp.; detected in soln. (decompn. on attempted isolation);