Mecanismo de adição de Michael

Mecanismo de adição de Michael, passo a passo

Cada etapa começa com o seu desenho, setas curvas incluídas; o texto abaixo dele descreve esse desenho.

1. Remove an alpha hydrogen

   

   The base removes the drawn hydrogen between the two carbonyls. This gives a resonance-stabilized enolate, with its lone pair drawn on carbon, and an alcohol that can give the proton back later.

   As setas curvas do desenho:

   • The base uses a lone pair to bond to the drawn hydrogen.
   • The bond to hydrogen breaks, leaving its electrons on the atom that lost H.

2. Attack the beta carbon

   

   Draw all three arrows together to add at the beta carbon. The attacked molecule becomes an enolate, not an alcohol. The original enolate donor keeps its carbonyl groups unchanged.

   As setas curvas do desenho:

   • The enolate carbon uses its lone pair to bond to the beta carbon.
   • The alkene π electrons form a bond toward the carbonyl carbon.
   • The C=O π electrons move to oxygen so carbon keeps eight electrons.

3. Alcohol gives back a proton

   

   The alcohol made in the first step gives its proton to the enolate carbon as the carbonyl returns. This regenerates the base without adding a workup reagent.

   As setas curvas do desenho:

   • Oxygen uses a lone pair to restore the C=O π bond.
   • The enolate π electrons form an alpha C–H bond with the drawn alcohol hydrogen.
   • The alcohol O–H electrons return to oxygen, regenerating alkoxide.

4. Products

   

   The new bond joins the donor alpha carbon to the acceptor beta carbon. The acceptor alpha carbon gains the hydrogen removed in the first step. The organic product is neutral, and the regenerated alkoxide carries the negative charge. The drawing shows which atoms are joined, not a preference for one stereoisomer.