Metal Fries rearrangement

Prior to solving the structure for SSZ-31, the catalytic conversion of hydrocarbons provided information about the pore structure such as the constraint index that was determined to be between 0.9 and 1.0 (45, 46). Additionally, the conversion of m-xylene over SSZ-31 resulted in a para/ortho selectivity of <1 consistent with a ID channel-type zeolite (47). The acidic NCL-1 has also been found to catalyze the Fries rearrangement of phenyl acetate (48). The nature of the acid sites has recently been evaluated using pyridine and ammonia adsorption (49). Both Br0nsted and Lewis acid sites are observed where Fourier transform-infrared (FT IR) spectra show the hydroxyl groups associated with the Brpnsted acid sites are at 3628 and 3598 cm-1. The SSZ-31 structure has also been modified with platinum metal and found to be a good reforming catalyst. 

More recently, Mouhtady et al. demonstrated that Bi(0Tf)3xH20 and other metal triflates interact with methanesulfonic acid (MSA) to form an efficient synergic catalytic system for the Fries rearrangement of naphthyl acetate [70, 71]. 

Focken, T. Hopf, H. Snieckus, V. Dix, I. Jones, P. G. Stereoselective lateral functionalization of monosubstituted [2.2]paracyclo-phanes by directed ortho metalation-homolo-gous anionic Fries rearrangement. Eur. J. Org. Chem. 2001, 2221-2228. 

Total synthesis has benefited from key DoM reactions. The sequence 48 —> 49 —> 50 —> 51 (Scheme 12) en route to the natural product ochratoxin A (52) takes multiple advantage of anion chemistry (53) ortho-metalation of the powerful OCONEtj group (step 1), anionic Fries rearrangement (step 2), in-between DoM and chain-extension by Li-Mg transmetalation (step 3) [12]. 

The starting point for the metallation sequence was /7-chlorophenol, whose directing power was first maximised by conversion to the carbamate 3. Ortholithiation and reaction with N,N-diethylcarbamoyl chloride gave the amide 4. The second ortho carbonyl substituent was then introduced simply by allowing the lithiated carbamate 5 to undergo an anionic ortho-Fries rearrangement to the bis-amide 6. The phenol was protected as its methyl ether 7. 

The O-carbamate, the most powerful of DMGs in competition experiments [13], is similarly plagued by stability as the N,N-diethyl derivative 13 (Scheme 6). However, the N-cumyl -N-methyl counterpart 14 undergoes unproblematic metalation-electrophile quench to give 15 and anionic Fries rearrangement (16) reactions. The very mild conditions for hydrolysis to 17, and hence to 18, as well as to 19 bode well for further useful chemistry of the N-cumyl DMG in context of more substituted aromatics [14]. 

Advantageously, catalytic amounts of rare earth metal triflates are used instead of stoichiometric amounts of aluminum trichloride in catalytic Fries rearrangements of carboxylic acid aryl esters furnishing keto building blocks, e.g. 10... 

The total synthesis of the potent protein kinase C inhibitor (-)-balanol was accomplished by J.W. Lampe and co-workers. They took advantage of the anionic homo-Fries rearrangement to prepare the sterically congested benzophenone subunit. To this end, 2-bromo-3-benzyloxy benzyl alcohol was first acylated with a 1,3,5-trisubstituted benzoyl chloride to obtain the ester precursor in 84% yield. Next, the ester was treated with n-BuLi at -78 °C to perform a metal-halogen exchange. The resulting aryllithium rapidly underwent the anionic homo-Fries rearrangement to afford the desired tetra ortho-substituted benzophenone in 51% yield. 

Charmant, J. P. H., Dyke, A. M., Lloyd-Jones, G. C. The anionic thia-Fries rearrangement of aryl triflates. Chem. Common. 2003, 380-381. Mouhtady, O., Gaspard-lloughmane, H., Roques, N., Le Roux, C. Metal triflates-methanesulfonic acid as new catalytic systems application to the Fries rearrangement. Tetrahedron Lett. 2003,44, 6379-6382. 

Metal triflates are efficiently utilized as reusable catalysts in the direct acylation of phenols as well as in the Fries rearrangement. Scandium triflate is employed as catalyst (5% mol) in the direct acylation of phenols and naphfhols wifh acyl chlorides in toluene-nitromefhane mix-fures af 100°C for 6 h. Resulfs from Table 5.3 show fhaf fhe reacfion is very efficienf complefe regioselecfivify is observed wifh mefa-cresol and 1-naphfhol derivafives. 

These results confirm that the Fries rearrangement can be performed in the presence of specific transition metal triflates as homogeneous, highly active catalysts with low toxicity, moisture and air tolerance. However, the high cost of these catalysts limits their use to small-scale production. 

Ortho-specific metal-promoted Fries rearrangement can be achieved, starting from orffeo-bromophenyl esters and sec-butyllithium. The reaction is performed at -95°C with 4 1 1 tetrahydrofuran diethyl ether hexane ratio followed by stirring for 30 min, followed by an additional 30 min at 78°C. The orfto-hydroxyaryl ketones are the sole isomers obtained, and the regioisomeric para-hydroxyaryl ketones are not obtained (Table 5.11). 

Anionic ortho-Fries rearrangement is performed by freafment of variously subsfifufed aryl carbamates with sec-butyllithium at -78°C in tetramethylethylenediamine-tetrahydrofuran solution for 8-12 h. i The reaction involves the selective ortho-metalation of fhe aryl groups. The meta-cooperafive mefalafion effect is responsible for fhe producfion of some extremely hindered aromatic compounds (Table 5.13). 

Kobayashi, S., Moriwaki, M., and Hachiya, I. 1997. The catalytic Fries rearrangement and o-acylation reactions using group 3 and 4 metal triflates as catalysts. Bull. Chem. Soc. Jpn. 70 267-273. 

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