Question

Identify R and S in the following reaction sequence, and draw a mechanism for the conversion of R to S (molecular formula ). S was used in the synthesis of darunavir (trade name Prezista), used to treat HIV.

Short answer

The ozonolysis occurs on the alkene. It forms aldehyde or ketone or both. The substituted carbon forms ketone and the unsubstituted carbon forms aldehyde in the presence of a reducing agent.

Step-by-step solution

Ozonolysis

The ozonolysis occurs on the alkene. It forms aldehyde or ketone or both. The substituted carbon forms ketone and the unsubstituted carbon forms aldehyde in the presence of a reducing agent.

Reducing agent

The sodium borohydride is the reducing agent which reduces aldehyde and ketone into the corresponding alcohol.The alcohol further undergoes intramolecular reaction forming the final product after abstraction of acidic hydrogen.

Explanation

The ozonolysis forms the aldehyde, which is further reduced from the sodium borohydride and forms the alcohol after workup.

The step-by-step reaction mechanism is as follows:

First Step

Second Step