Question

The reaction(s) in which inversion of configuration occur(s) is(are)

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

\textbf{Mitsunobu} \(=\) activated alcohol \(\mathrm{S_N2}\) \(\Rightarrow\) inversion.
\textbf{Neighboring-group participation} (acyloxonium/thiiranium/halonium) often leads to backside opening \(\Rightarrow\) inversion at the attacked carbon.
\textbf{Rearrangements} like Hofmann and Baeyer–Villiger are concerted migrations \(\Rightarrow\) \emph{retention} of configuration at the migrating center.

Answer 1

The Correct Option is A, B

Step 1: Option (A) — Mitsunobu reaction.
\(Ph\textsubscript{3}\)P/DEAD with a carboxylic acid converts an alcohol \(\ce{R^\*–OH}\) into the corresponding ester \(\ce{R^\*–O_2CR'}\) via an \(\mathrm{S_N2}\) displacement of the \(\ce{O–PPh_3}\) activated intermediate. The chiral center at carbon undergoes a single backside attack \(\Rightarrow\) Walden inversion.
Step 2: Option (B) — Anchimeric assistance (acyloxonium) under heat.
On heating, the neighboring acetate participates to form a cyclic \emph{acyloxonium} intermediate; subsequent intramolecular/backside attack (or acetate capture) occurs \(\mathrm{S_N2}\)-like. The carbon bearing the leaving group is attacked from the opposite face \(\Rightarrow\) inversion at that stereocenter. (This is the classic neighboring-group participation in constrained bicyclic/allylic systems.)
Step 3: Option (C) — Hofmann rearrangement.
\(\ce{NaOBr}\) converts an amide to a \(\ce{C{-}1}\) shorter amine via \(\ce{N}\)-bromoamide, rearrangement, and isocyanate. Stereochemical information at a migrating \(\alpha\)-carbon (if present) is \emph{retained} through the concerted migration; no inversion is involved.
Step 4: Option (D) — Baeyer–Villiger oxidation.
Peracid inserts an oxygen adjacent to a carbonyl with migration of one substituent. The migrating stereocenter (if any) migrates \emph{with retention} (concerted rearrangement), not inversion.
Therefore, only (A) and (B) involve inversion of configuration.