In the following transformation, the enantiomerically pure lactone A provides

Concept:

​Activation of allylic electrophiles by palladium(0):

• Allylic compounds with a good leaving group can form a π-allyl cation complex of palladium (0) via nucleophilic displacement reaction with controlled stereochemistry and regiochemistry.
• The π-allyl cation complex gives the product upon attack by a nucleophile.
• An example is shown below:

• The reaction usually proceeds with the retention of configuration at the reacting center.

Explanation:

• The reaction pathway is shown below:

• From the above reaction, we can see that the reaction proceeds with the retention of configuration at the reacting center. It also suggests a double
  inversion.
• The Coordination of Pd occurs to the double bond of the allylic lactone A on the less hindered face opposite to the leaving group. Also, we may think of the oxidative addition step as an invertive nucleophilic displacement of the leaving group by a pair of Pd electrons.
• In the last step, the nucleophile then adds to the face of the π-allyl Pd cation complex opposite of the Pd metal.
• This results in the formation of a syn-diastereomer B, which is racemic.

Conclusion:

Hence, In the following transformation, the enantiomerically pure lactone A provides only syn-diastereomer of B, which is racemic.