Allen-Millar-Trippett Rearrangement is the ring expansion of cyclic phosphonium salts to form dihydro phosphinine.Cyclic Phosphonium salts are obtained by reacting Cyclic phosphines with Alkyl halides or acyl halides in presence of base like triethylamine.
Mechanism:
The Lone electrons of the phosphorous atom of cyclic phosphine attack the carbon atom of acyl halides to form a phosphonium ion. After that, when refluxed with water, undergoes a rearrangement reaction to form dihydro phosphinine.
