Question

Choose the correct option(s) with regard to mechanism of the following transformation. 

• A. It proceeds through divinyl cyclopropane rearrangement
• B. It involves a diradical intermediate
• C. It proceeds through di-\(\pi\)-methane rearrangement
• D. It proceeds through [2+2+2] cycloaddition reaction

Hint:

Di-\(\pi\)-methane rearrangement is a photochemical reaction often involving diradicals and leads to rearranged bicyclic products from allyl or benzylic systems under UV light.

Answer 1

The Correct Option is B, C

The reaction shown is a classic example of the di-\(\pi\)-methane rearrangement, a photochemical reaction. Upon irradiation with UV light, a system containing a conjugated diene and a methylene bridge undergoes a rearrangement that involves:

• Excitation of the molecule to a singlet or triplet excited state.
• Formation of a diradical intermediate.
• Rearrangement to a bicyclo[3.1.0]hexane-type product via a 1,2-shift.

Let’s evaluate each option:

• (A) Divinyl cyclopropane rearrangement is not applicable here. WRONG
• (B) Correct – the reaction proceeds via a diradical intermediate. CORRECT
• (C) Correct – this transformation is a di-\(\pi\)-methane rearrangement. CORRECT
• (D) [2+2+2] cycloaddition is not the mechanism here. WRONG

\[ \boxed{\text{Correct options: (B) and (C)}} \]