Why is a Mitsunobu reaction stereo selective?

A Mitsunobu reaction is stereo selective because it allows for the inversion of stereochemistry at an alcohol's stereocentre.

The Mitsunobu reaction is a powerful tool in synthetic chemistry, named after its discoverer, Oyo Mitsunobu. It is a process that involves the conversion of primary or secondary alcohols into a variety of functional groups, such as esters, ethers, and amines. The reaction is particularly noted for its stereo selectivity, which is the ability to preferentially form one stereoisomer over another in a chemical reaction.

The stereo selectivity of the Mitsunobu reaction is due to the mechanism of the reaction. The reaction involves the use of a nucleophile, a compound that can donate an electron pair to an electrophile to form a chemical bond. In the Mitsunobu reaction, the nucleophile attacks the stereocentre of the alcohol from the opposite side, leading to an inversion of stereochemistry. This is similar to the way in which a backside attack occurs in an SN2 reaction.

The stereo selectivity of the Mitsunobu reaction is also influenced by the choice of reagents. The reaction typically involves the use of a triphenylphosphine and a diazo compound, which together form a phosphonium ylide. This ylide is a strong nucleophile and can attack the stereocentre of the alcohol from the backside, leading to an inversion of stereochemistry.

In summary, the Mitsunobu reaction is stereo selective due to the mechanism of the reaction, which involves a backside attack on the stereocentre of the alcohol, and the choice of reagents, which form a strong nucleophile that can carry out this attack. This allows for the selective formation of one stereoisomer over another, making the Mitsunobu reaction a valuable tool in synthetic chemistry.