(Z)-(E) INTERCONVERSION OF OLEFINS BY THE ADDITION-ELIMINATION SEQUENCE OF THE (TMS)(3)SI. RADICAL

Tris(trimethylsilyl)silyl radical is effective in isomerizing either acyclic or cyclic olefins by an addition-elimination sequence. The E/Z ratio after equilibration generally reflects the thermodynamic stability of (Z)- and (E)-alkenes. It has been shown for (E)- and (Z)-hexen-1-ol that equilibration (Z/E = 18/82) is reached with the (TMS)(3)Si . radical in 10 h at 80 degrees C, whereas with PhS . and Bu(3)Sn . radicals the same isomeric composition is reached in 1 and 4 h, respectively. In cyclic systems like (Z)-cyclododecene the ratio of Z/E = 46/54 is reached in 8 h, while with PhS . and Bu(3)Sn . it is much slower. An explanation of this phenomenon has been advanced. Additional information on the impact of this addition-elimination methodology in organic synthesis is given.