Arylation benzyl alcohols

The value of such heteroatom-> C rearrangements has been expertly demonstrated by Clayden and coworkers when it was shown that substituted diaryhnethylamines could be prepared by a stereospecific intramolecular electrophilic arylation of hthiated ureas [17], This work was soon followed-up and developed further to produce a-arylated cyclic amines [18], a-arylated benzylic alcohols [19], an asymmetric synthesis of clemastine (Scheme 18.5) [20], a sequential double a-arylation of A -allylureas by asymmetric deprotonation and N C aryl migration [21], and a simple method for the synthesis of tertiary thiols and thioethers [22], and tertiary alcohols [23], all involving a Truce-Smiles rearrangement. 

C) Carboxylic adds For aryl-substituted alcohols, such as benzyl alcohol, oxidation readily gives the corresponding add (c/. p. 336). 

In the reaction of aryl and alkenyl halides with 1,3-pentadiene (248), amine and alcohol capture the 7r-allylpalladium intermediate to form 249. In the reactions of o-iodoaniline (250) and o-iodobenzyl alcohol (253) with 1,3-dienes, the amine and benzyl alcohol capture the Tr-allylpalladium intermediates 251 and 254 to give 252 and 255[173-175]. The reaction of o-iodoaniline (250) with 1,4-pen tadiene (256) affords the cyclized product 260 via arylpalladiuni formation, addition to the diene 256 to form 257. palladium migration (elimination of Pd—H and readdition to give 258) to form the Tr-allylpalladium 259, and intramolecular displacement of Tr-allylpalladium with the amine to form 260[176], o-Iodophenol reacts similarly. 

Section 1115 The simplest alkenylbenzene is styrene (C6H5CH=CH2) An aryl group stabilizes a double bond to which it is attached Alkenylbenzenes are usu ally prepared by dehydration of benzylic alcohols or dehydrohalogena tion of benzylic halides... 

Substitution Reactions on Side Chains. Because the benzyl carbon is the most reactive site on the propanoid side chain, many substitution reactions occur at this position. Typically, substitution reactions occur by attack of a nucleophilic reagent on a benzyl carbon present in the form of a carbonium ion or a methine group in a quinonemethide stmeture. In a reversal of the ether cleavage reactions described, benzyl alcohols and ethers may be transformed to alkyl or aryl ethers by acid-catalyzed etherifications or transetherifications with alcohol or phenol. The conversion of a benzyl alcohol or ether to a sulfonic acid group is among the most important side chain modification reactions because it is essential to the solubilization of lignin in the sulfite pulping process (17). 

Aiyl esters, prepared from the phenol and an acid chloride or anhydride in the presence of base, are readily cleaved by saponification. In general they are more readily cleaved than the related esters of alcohols, thus allowing selective removal of phenolic esters. 9-Fluorenecarboxylates and 9-xanthenecarboxylates are also cleaved by photolysis. To permit selective removal, a number of carbonate esters have been investigated aryl benzyl carbonates can be cleaved by hydrogenolysis aryl 2,2,2-trichloroethyl carbonates, by Zn/THF-H20. 

SnBr2, AcBr, CH2CI2, rt, 81-92% yield. These conditions, which also cleave alkyl and aryl benzyl ethers, produce an acetate that must then be hydrolyzed with base to release the alcohol. When SnCl2/PhOCH2COCl is used, only MPM ethers are cleaved, leaving benzyl ethers unaffected. 

In this example, sodium in r-butyl alcohol cleaves two aryl benzyl ethers and reduces a double bond that is conjugated with an aromatic ring non-conjugated double bonds are stable. 

In 1983, Nozaki, Takai, Hiyama, and their coworkers disclosed that vinyl and aryl iodides or bromides are reduced with chromium(n) chloride, and that the resulting organochromium(in) species react smoothly with a host of aldehydes to give allylic or benzylic alcohols in excellent yields.6 As shown in Scheme 1, the chromium(n) chloride-mediated carbonyl addition can be conducted efficiently at... 

Scheme 13 Iron(III)-catalyzed addition of benzylic alcohols to aryl alkynes...

Scheme 15 Iron(III)-mediated synthesis of alkenyl halides via direct C-C bond formation of benzylic alcohols and aryl alkynes...

Scheme 16 sp-sp C-C bond formation via Fe(OTf)3ATfOH-cocatalyzed coupling reaction of terminal aryl alkynes with benzylic alcohols... 

Table 5 Reaction of an ori/zo-substituted aryl iodide with benzyl alcohol in the presence of K2C03, Pd(OAc)2 and norbomene.1...

General procedure for the reaction of an o-substituted aryl iodide in the presence of benzyl alcohol. Synthesis of biphenyl derivatives. 

Reaction of 2-amino-benzyl alcohol and 2-chloroH-phcnylaminopyrimidinc forms the intermediate cation 204, which contains ene and iminium functionalities and undergoes electrocyclic rearrangement to the 2-phenylamino-6//-pynmido[2,l-2 ]quinazoline 205 (Scheme 32). The cation 204 is stabilized by the aryl groups. The 2-NHPh stmcture of the product was confirmed by 111 NMR spectroscopy <2002TL1303>. 

The combination Et3SiH/(C6F5)3B reduces acid chlorides to methyl groups (Eq. 138).281,282 If a smaller amount of triethylsilane is used, the same combination reduces aryl acid chlorides to the trimethylsilyl ethers of the benzyl alcohols.281,282... 

The PMHS/TBAF system provides both an excellent and practical approach to the reduction of aryl ketones to the benzyl alcohols.278 Similarly, the PMHS/ Triton B combination gives high yields of the benzyl alcohols.278... 

Benzyl alcohols Aryl alkyl carbinols (11) can be oxidized to ketones (12) by the direct electrochemical method (Eq. 4) since they possess their oxidation potentials at around 2.0 V versus SCE (saturated calomel electrode) however, cleavage products decrease the selectivity [14]. 

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