O-allylation of phenol

Although palladium catalysts have played the most prominent role in this area, other metals have also been found to catalyze allylic etherification reactions, often providing complementary stereochemical outcomes. A few ruthenium catalyst systems have been used for the O-allylation of phenols,143,144 including an enantioselective version utilizing [Cp Ru(MeCN)3]PF6 that provides promising ee s, albeit with diminished control of regioselectivity (Equation (25)).145... 

The palladium(0)-catalyzed asymmetric O-allylation of phenols has been described using five-, six- and seven-membered ring allylic carbonates and acyclic allylic carbonates (eq 9). The products from these reactions were subjected to a Claisen rearrangement to provide C-alkylated phenols. A study of various ligands for the reaction of phenol with 2-cyclohexenyl-l-methyl carbonate clearly showed that the Trost ligand is superior. ... 

The most common preparative method to prepare the aryl allyl ether is the Williamson s ether synthesis [la,b]. Typically, aryl allyl ethers can be obtained from phenol derivatives and allylic halide under basic conditions (KjCOj) in refluxing acetone. This method is convenient for the preparation of simple allyl aryl ethers. However, some side reactions such as a competitive C-allylation (Sn2 type reaction) often accompany the formation of undesired byproducts. Mitsunobu reaction of phenol derivatives with allylic alcohols instead of allylic halides can be used under mild conditions [13]. In particular, when the allyl halide is unstable, this procedure is effective instead of the Williamson s ether synthesis. This method is also useful for the preparation of chiral allyl aryl ether from chiral allylic alcohol with inversion at the chiral center. Palladium catalyzed O-allylation of phenols is also applicable, but sometimes a lack of site-selectivity with unsymmetrical allylic carbonate [14] may be a problematic issue. 

Manikandan R, Prakash G, Kathirvel R, Viswanathamurthi P (2013) Ruthenium(II) carbonyl complexes bearing quinoline-based NNO tridentate ligands as catalyst for one-pot conversion of aldehydes to amides and o-allylation of phenols. Spectrochim Acta A Mol Biomol Spectrosc 116 501-508... 

Phenols arc highly reactive O-nucleophiles and allylated easily with allylic carbonates under neutral conditions. EWGs on phenols favor the reac-tion[213], Allylic acetates are used for the allylation of phenol in the presence of KF-alumina as a base[214]. 

Claisen, L., Eisleb, O. Rearrangement of phenol allyl ethers into the isomeric allylphenols. Ann. 1914,401, 21-119. 

Highly stereoselective [3,3]-sigmatropic rearrangement of allyl vinyl or allyl aryl ethers to yield y,6-unsaturated carbonyl compounds or o-allyl substituted phenols, respectively ... 

O-Methylation of phenolic compotmds can be efficiently carried out by tetra-methylammonium chloride in diglyme or poly ethyleneglycol (PEG) at temperatures of 150-160 °C and in the presence of either NaOH or K COj. The benzylation and methylation of phenols occiu, where the benzylation product was always predominating. With allyl-substituted phenols as substrates and using NaOH as a base, it was feasible to achieve both the alkylation and the double-bond isomerization of the allyl group to obtain (E/Z)-propenyl-substituted methyl and benzyl aryl ethers in a single preparative step (Maras et al., 2010). 

Early studies on the photochemistry of o-allyl-substituted phenols indicated that photolysis generally gave mixtures of benzofuran and benzopyran cyclization products (i.e., 46 and 47 from 45) ... 

Claisen rearrangement (Section 24 13) Thermal conversion of an allyl phenyl ether to an o allyl phenol The rearrange ment proceeds via a cyclohexadienone intermediate... 

The discovery of the utility of the bis-chromone carboxylic acid derivative cromolyn sodium in the treatment of asthma and related allergies has led to an intensive, and thus far not very fruitful, effort to discover analogues which would show oral activity in contrast to the lead which must be administered by inhalation. Preparation of a typical analogue, proxicromil (63), starts with the O-allylated phenol 57. Claisen rearrangement leads to the corresponding C-allylated product 58. 

The rearrangement of an O-allyl ether (LXXV) to form the isomeric ortho allyl phenol (LXXVI)... 

Some allyl phenyl ethers with an alkyl substituent on the end carbon of the allyl group rearrange to give the normal ortho-Claisen product together with another isomeric O-allyl phenol. The latter, formed by the rearrangement of the normal product, has been established. This is called abnormal Claisen rearrangement, is illustrated by the following example. 

The cationic complex [Ni(bpy)3](BF4)2 is a good catalyst for the electroreductive cleavage of the C—O (allyl) bond of allyl ethers, affording parent alcohols or phenols. The Ni(II)-catalyzed electroreductive deprotection of allyl ethers is found to proceed in a DMF-Bu4NBp4-(Mg) system. For... 

The ring closure of o-allyl phenols has been extended to the synthesis of several other types of fused furans. 

Synthesis of 2-(1-Hydboxyalkyl)-2,3-dihydrobenzofttrans fbom o-Allyl Phenols (168) AND... 

AHC(18)337>. The 3-alkylbenzo[6 ]furans result from cyclodehydration of aryloxyacetones the most common dehydrating agents are sulfuric acid, phosphorus oxychloride and poly-phosphoric acid. The allyl ethers of phenols can be converted to 2-alkyl-2,3-dihydro-benzo[6]furan by heating with polyphosphoric acid, pyridine hydrochloride or magnesium chloride at 180 °C the intermediate o-allylphenol is not isolated. 

The allyl ethers of phenols may be converted via a Claisen rearrangement to o-allyl derivatives and thence to the benzo[6]furans. The products of addition of bromine to the o-allylphenols give good yields of the heterocycle on prolonged heating with alkali, but the photochemical rearrangement of O-allylphenol is not so effective. 

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