Elimination reactionsSynthesis from an Ester
Figure 135 Synthesis of alcohol from an ester and Grignard reagent
The image above shows the synthesis of an alcohol from an ester reacted with a Grignard
reagent. When an ester is the target of the Grignard’s attack, the result is a tertiary alcohol
and a primary alcohol. The primary alcohol is always from the -O-R portion of the ester
and the tertiary alcohol is the other R groups of the ester combined with the R group from
the Grignard reagent.
Synthesis from an Epoxide
Figure 136 Synthesis of alcohol from an epoxide and Grignard reagent
We will discuss reactions with Epoxides later when we cover epoxides, but for now, we’ll
briefly discuss the synthesis of an alcohol from an epoxide. The nature of the reaction is
different than with the carbonyls, as might be expected. The reaction of Grignard reagents
with epoxides is regioselective. The Grignard reagent attacks at the least substituted side
of the carbon-oxygen bonds, if there is one. In this case, one carbon has 2 hydrogens and
the other has 1, so the R group attacks the carbon with 2 hydrogens, breaking the bond
with oxygen which is then protonated by the acidic solution. leaving a secondary alcohol
and a concatenated carbon chain. The R group can be alkyl or aryl.
Organolithium Alternative
As an alternative to Grignard reagents, organolithium reagents can be used as well. Organo-
lithium reagents are slightly more reactive, but produce the same general results as Grignard
reagents, including the synthesis from epoxides.