Deoxyprepacifenol NSC611358 Spiro[cyclohexane-1,2'-[7]oxabicyclo[4.1.0]hept[4]ene], 3,4'-dibromo-4-chloro-1',3',3',4-tetramethyl-, [1R-[1.alpha.,(1'S*,6'R*),3.beta.,4.alpha.]]-