efaq: No Escape key

 
 9.10 What if I don’t have an <Escape> key?
 ==========================================
 
 Type ‘C-[’ instead.  This should send ASCII code 27 just like an Escape
 key would.  ‘C-3’ may also work on some terminal (but not under X). For
 many terminals (notably DEC terminals) <F11> generates <ESC>.  If not,
 the following form can be used to bind it:
 
      ;; F11 is the documented ESC replacement on DEC terminals.
      (define-key function-key-map [f11] [?\e])