The Zimmerman Traxler Model
   Overview: The Zimmerman-Traxler model is invoked to rationalize the unexpected 
   stereochemical outcomes of certain aldol reactions, such as the Reformatsky and 
   Ivanov reactions. It models the stereochemistry of the products, based on the steric 
   hindrance in the possible six-membered transition states in the aldol condensation 
   reactions.
   Enolate Formation
  Wiki Page: Aldol Reaction- Traxler Model
  1. Zimmerman and Traxler, JACS, 1957 79 (8)
  The Zimmerman Traxler Model
  Overview: The Zimmerman-Traxler model is invoked to rationalize the unexpected 
  stereochemical outcomes of certain aldol reactions, such as the Reformatsky and 
  Ivanov reactions. It models the stereochemistry of the products, based on the steric 
  hindrance in the possible six-membered transition states in the aldol condensation 
  reactions.
  Possible Transition States
               E-enolate
               Z-enolate
 Wiki Page: Aldol Reaction- Traxler Model
 1. Zimmerman and Traxler, JACS, 1957 79 (8)
    Examples
         Ivanov
         Reaction
         Reformatsky
         Reaction
         It   was  noted  that  these  reactions  produced  products  with  very  high 
         enantioselectivity, however, the rationale for this was not determined until the 
         work of Zimmerman and Traxler. For this to be useful, however, there must be 
         some control over the enolate formation, as this is the determining factor for the 
         stereochemical  induction.  This  knowledge  proves  to  be  useful  in  synthesis 
         where enantioselectivity is necessary. 
   Zimmerman and Traxler, JACS, 1957 79 (8)
   Wikipedia pages: Reformatsky; Ivanov
  Experimental Observation
  Chair-like vs. Boat-like intermediates:
  It was recognized prior that the metal enolate, as well as the stereochemistry of the 
  alkene, had an effect on product selectivity. With this information and more, it was 
  deduced that the stereoselectivity of the products indicated the chair-like intermediate. 
   
  Lui et. Al. have shown that the Zimmerman-Traxler model for the intermediate of the 
  selective  reaction  prevails  over  boat-like  intermediates  with  a  ratio  of  50  to  1 
  respectively. 
 Lui et. al. JACS 2005, 127 (16), pp 5770–5771
  Problems
  1. Draw a Zimmerman-Traxler transition state model for the following reactions. 
  2. Draw the major product for the reactions above.
  3. Repeat questions 1 and 2 for the following Reformatsky type reaction.
  1 & 2. Reiser, O. Chem. Rev. 1999, 1191
  3. Choppin et. al. Chem. Soc. Rev., 2013,42, 937-949