Question

Two products are formed in the following [1,7] sigmatropic rearrangement, one due to hydrogen migration and the other to deuterium migration. Show the configuration of the products by replacing A and B with the appropriate atoms (H or D).

Short answer

The replacement of A and B with H and D is given below.

Step-by-step solution

Sigmatropic rearrangement

Sigmatropic reactions involve the cleavage of the sigma bond in the reactant, the formation of a new sigma bond, and the rearrangement of the pi bond. The word “sigmatropic” means “sigma-change.”

Configuration of the products by replacing A and B with H and D

The reaction given below is a [1,7] sigmatropic rearrangement.

[1,7] sigmatropic rearrangement

The reaction includes four pairs of electrons, and an antrafacial rearrangement takes place in it. Hence, when H migrates, as it is situated above the plane of the reactant, it ends up below the plane of the reactant molecule.

When D migrates, as it is below the plane of the reactant molecule, it ends up above the plane of the product molecule.

A and B in the product can be replaced by H and D appropriately, as shown below

Replacement of A and B with H and D