Question

Greg Nard added an equivalent of 3,4-epoxy-4-methylcyclohexanol (Figure 1) to an ether solution of methyl magnesium bromide and then added dilute hydrochloric acid. Heexpected that the product would be a diol (Figure 2). He did not get any of the expected product. What product did he get?

Answer 1

Concepts and reason

The problem is based on the concept of Grignard reagent.

Grignard reagent is an organometallic compound which is formed by the reaction of magnesium metal with alkyl halides. They are extermely good nucleophiles and thus, reacts with electrophiles such as epoxides and carbonyl compounds (aldehyde, ketone, esters) to form new carbon –carbon bonds. Grignard reagents are also used as very strong bases and thus, they reacts with acidic compounds such as alcohols, carboxylic acid to form alkoxide ions.

Epoxides are three-membered ring structures which contain an oxygen atom at one vertices and two carbon atoms at other two vertices. The carbon atoms in epoxides ring are electrophilic and therefore, reacts with nucleophile which opens the strained ring. An example of ring-opening of epoxide is as follows:

Fundamentals

Grignard reaction: Grignard reagents are rich source of nucleophiles, which are useful intermediates in organic synthesize.

Representative example for Grignard reagent preparation and its reaction:

Typical example for ring opening of epoxide was given below:

The acid-base reaction between and is as follows:

Ringing opening of epoxide by

Ans:

The product of the reaction is as follows:

Answer 2

Epoxide rings are readily opened with cleavage of the carabon-oxygen bond when attacked by nucleophiles. Grignard reagents and organolithium reagentsreact with etylene oxide by serving as sources of nucleophilic carbonThe reaction of Grignard reagents with epoxides is regioselective. Attack occurs at the less substituted carbon of ring.