Rearrangement benzylic acid

Benzylic acid rearrangement, 836 Benzylic carbocation, electrostatic potential map of, 377 resonance in, 377 SN1 reaction and, 376-377... 

On treatment of the quinone (109) with NaOH in a dioxane-water mixture (1 1) at 100° for several days a benzylic acid rearrangement takes place giving phenanthro-[3,4-c]fluorene (110) in 52% yield U3>. 

Keywords benzil, alkyli metal hydroxide, benzylic acid rearrangement, benzylic acid... 

On the basis of these results, the benzyl-benzylic acid rearrangement 179 180 -> 181 should occur with stereoelectronic control. The stereochemistry of the transposition should be as depicted by 182 +183. 

If the MeO group is replaced by a leaving group such as MsO, it can exercise the pull and the carbonyl can provide the push after it has been attacked by a nucleophile. This next five-membered cyclic ketone fragments on treatment with base—can you detect hints of the benzylic acid rearrangement ... 

Because of their relatively high reactivity, the foregoing structures often appear as transient intermediates in a series of reactions rather than as end products. Several of the documented reactions of these intermediates include rearomatization (e.g., reduction to catechol and hydroquinone derivatives), further oxidation to mono- and dicarboxylic acids (see below), benzylic acid rearrangements (Corbett 1966, Corbett and Fooks 1967), cycloaddition reactions (Teuber et al. 1966), and various condensation reactions (Erdtman and Granath 1954). The last-named processes, which are accelerated in acidic and basic media, often give rise to structurally complex and poorly defined materials. 

An interesting ring-contraction biogenetic pathway from puupuhenone (45) to haterumadienone (46) might proceed via benzylic acid rearrangement of the diketone form of 45, followed by oxidative decarbonylation. Haterumadienone (46) is the first ring-contracted... 

In the benzylic acid rearrangement of 1,2-diketones, HO adds to one ketone. The tetrahedral intermediate can collapse by expelling HO-, giving back starting material, or it can expel Ph-. The Ph- group leaves because there is an adjacent electrophilic C to which it can migrate to give the product. 

The Favorskii rearrangement differs from the benzylic acid rearrangement in that the a-carbon is a cr-bond electrophile rather than a 7r-bond electrophile. 

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