When an electron-attracting aromatic group (IC) is used instead of a phenyl group (la), the isomerization is slowed down but the yield is identical (65-70%). In contrast, the tolyl group enhances the dehydration rate of diol (4b) but decreases the yield to about 35%. There is probably, in the first ionization step, more benzylic carbocation leading to the classical dehydration, with migration of the ethylenic gr0up. l
