Question

The major product obtained in the given reaction is :

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

AlCl₃ ionises the secondary C-Cl bond to a carbocation, which attacks the ring intramolecularly (Friedel-Crafts alkylation) to close a six-membered ring at the less hindered ortho position (para to CH₃).

Answer 1

The Correct Option is C

The substrate is 3-methylphenyl 3-chlorobutyl ether: m-CH₃-C₆H₄-O-CH₂-CH₂-CHCl-CH₃.
Step 1: AlCl₃ abstracts Cl^-, giving the secondary carbocation ArO-CH₂-CH₂-CH⁺-CH₃.
Step 2: The electron-rich ring (activated by OR) attacks the cation in an intramolecular Friedel-Crafts alkylation. Attack at the ortho position of the O-substituent closes a six-membered ring (O, 2 CH₂, CH, and two ring carbons) = chroman.
Step 3: The two ortho positions of OR are C2 (between OR and CH₃, sterically crowded) and C6 (para to CH₃, favourable, also activated by CH₃). Closure at C6 puts the CH₃ on C-7 of the chroman and the new CH₃ on C-4: 4,7-dimethylchroman.
Options (1) and (2) are alkenes (elimination), and option (4) is the 4,5-dimethyl isomer formed by hindered closure.
Answer: (3) 4,7-dimethylchroman