20  US 6,767,687 Bl  19  -continued  -continued  CH 3  I  O=C-O-C-CH  I  I  3  0  CH3  0 -r 0 -0-9  w,-0-cn,  CH3-t-cH 3  ¢  CH$_{3 }$ 0  CH3  I  I  o=c-o-c-cH  I  3  CH$_{3 }$ CH$_{3 }$ o=c-o-b-cH  I  I  3  0 -ro-O-s  CH3-,-CH3  D  ~03  I  ¢  CH30  CH$_{3 }$ 0  CH3  I  I  o=c-o-c-cH  I  3  CH 3  9  on-0-~,,-0-cn,  OH  OH  OH-0-s+  ,  ¢  1 H$_{2 }$ o  S0$_{2 }$ OH  TI  f83  !  s- CF3S04- CH3-t-CH3  ¢  CH$_{3 }$ CH$_{3 }$ I  O-C-O-C-CH  II  I  3  0 