Gas-phase carbanion rearrangements. Deprotonated benzyl and allyl ethers

Abstract

The following systems have been studied: (i) the ion PhOPh₂ on collisional activation undergoes Wittig rearrangement to Ph₃CO^– before fragmentation; (ii) PhOHCHCH₂ undergoes competing rearrangements, viz. Wittig rearrangement to Ph(CH₂CH)CHO^– and anionic Claisen rearrangement to (HO) deprotonated o-allylphenol, with the former reaction predominating; (iii) deprotonation of dibenzyl ether yields an unstable species which forms PhCH₂^–: no Wittig rearrangement is observed in the gas phase although it occurs in the condensed phase; and (iv) PhCH₂OCH₂CHCH₂ deprotonates to form the two interconvertible anions PhHOCH₂CHCH₂ and PhCH₂OHCHCH₂ of which the former is the more stable. Both ions give minor Wittig products, but the major process is loss of H₂O to form a deprotonated dihydronaphthalene. There is some analogy between gas-phase and condensed-phase reactions in this system. The condensed-phase reaction of allyl benzyl ether under forcing conditions (lithium di-isopropylamide/tetrahydrofuran–hexamethylphosphoramide) gives the products 1-phenyl-but-3-en-1-ol, 1,2-dihydronaphthalene, and 1-(o-tolyl)prop-2-en-1-ol in the approximate ratio 4 : 3 : 1.