Benzylic groups

Synthesis It might be better to add the benzyl group at the end so that we ean use dim ethyl amine. 

The benzyl group has been widely used for the protection of hydroxyl functions in carbohydrate and nucleotide chemistry (C.M. McCloskey, 1957 C.B. Reese, 1965 B.E. Griffin, 1966). A common benzylation procedure involves heating with neat benzyl chloride and strong bases. A milder procedure is the reaction in DMF solution at room temperatiue with the aid of silver oxide (E. Reinefeld, 1971). Benzyl ethers are not affected by hydroxides and are stable towards oxidants (e.g. periodate, lead tetraacetate), LiAIH, amd weak acids. They are, however, readily cleaved in neutral solution at room temperature by palladium-catalyzed bydrogenolysis (S. Tejima, 1963) or by sodium in liquid ammonia or alcohols (E.J. Rcist, 1964). 

When the benzene ring is named as a substituent the word phenyl stands for CgH5— Similarly an arene named as a substituent is called an aryl group A benzyl group IS CgHjCH,—... 

Allyl or benzyl groups on the nitrogen facilitate the process. The rearrangement appears to be intramolecular (13), proceeding by a cycHc mechanism as in the case of /V-2-buteny1-/V-metby1 aniline oxide giving /V-methyl-0-1-methylallyl-/V-phenyl-hydroxylamine. 

Catalyst Cation. The logarithms of extraction constants for symmetrical tetra- -alkylammonium salts (log rise by ca 0.54 per added C atom. Although absolute numerical values for extraction coefficients are vastly different in various solvents and for various anions, this relation holds as a first approximation for most solvent—water combinations tested and for many anions. It is important to note, however, that the lipophilicity of phenyl and benzyl groups carrying ammonium salts is much lower than the number of C atoms might suggest. Benzyl is extracted between / -propyl and -butyl. The extraction constants of tetra- -butylammonium salts are about 140 times larger than the constants for tetra- -propylammonium salts of the same anion in the same solvent—water system. 

Again, as with pyridopyrimidines, the main reaction is oxidation of di- or poly-hydro derivatives to fully aromatic structures, often merely by air or oxygen. In some cases the reagent of choice is mercury(II) oxide, whilst other reagents used include sulfur, bromine, chloranil, chromium trioxide-acetic acid, hydrogen peroxide, and potassium ferricyanide, which also caused oxidative removal of a benzyl group in the transformation (306) (307)... 

FeCl3, AC2O, 55-75% yield.The relative rates of cleavage for the 6-, 3-, and 2-O-benzyl groups of a glucose derivative are 125 24 1. Sulfuric acid has also been used as a catalyst. ... 

RUO2, NaI04, CCI4, CH3CN, H2O, 54-96% yield. In this case the benzyl group is oxidized to a benzoate that can be hydrolyzed under basic conditions. 

Na, NH3- Benzyl groups are also removed under these conditions. 

A benzylidene acetal is a commonly used protective group for 1,2- and 1,3-diols. In the case of a 1,2,3-triol the 1,3-acetal is the preferred product. It has the advantage that it can be removed under neutral conditions by hydrogenolysis or by acid hydrolysis. Benzyl groups and isolated olefins have been hydrogenated in the presence of 1,3-benzylidene acetals. Benzylidene acetals of 1,2-diols are more susceptible to hydrogenolysis than are those of 1,3-diols. In fact, the former can be removed in the presence of the latter. A polymer-bound benzylidene acetal has also been prepared." ... 

FeCl3, CH2CI2, 3-30 min, 68-85 % yield. Benzyl groups are also cleaved by this reagent. 

This acetal is stable to hydrogenation with W4-Raney Ni, which was used to cleave a benzyl group in 99% yield. ... 

CF3OSO2F or CH3OSO2F, PhSCH3, CF3CO2H, 0°, 30 min, 100% yield. Thioanisole suppresses acid-catalyzed rearrangement of the benzyl group to form 3-benzyltyrosine. The more acid-stable 2,6-dichlorobenzyl ether is cleaved in a similar manner. 

Treatment of a tertiary benzylamine also affords the Troc derivative with cleavage of the benzyl group (CI3CCH2OCOCI, CH3CN, 93% yield). ... 

The Teoc derivative can be prepared by cleavage of an N-Bn bond with Teoc-Cl in THE. This is a general method for removal of benzyl groups from nitrogen. Methyl and ethyl groups are also cleaved, but more slowly (24 h vs. 4 h) and in lower yield ... 

Me,SiCl, PhOH, CH2CI2, 20 min, 100% yield.Under these conditions benzyl groups are not cleaved. 

KOH, H2O, reflux, 12 h, 64-92% yield. This group is more stable to n-BuLi than is the benzyl group when used to protect imidazoles. 

With H2/Pd-C, the normal conditions for benzyl group removal, it is difficult to remove the benzyl group on histidine without also causing reduction of other aromatic groups that may be present. ... 

Methods 7 and 8 were used to remove the benzyl group from a biotin precursor. 

Some of the methods used to cleave the benzyl group should also be effective for cleavage of the MPM group. ... 

This procedure is representative of a new general method for the preparation of noncyclic acyloins by thiazol ium-catalyzed dimerization of aldehydes in the presence of weak bases (Table I). The advantages of this method over the classical reductive coupling of esters or the modern variation in which the intermediate enediolate is trapped by silylation, are the simplicity of the procedure, the inexpensive materials used, and the purity of the products obtained. For volatile aldehydes such as acetaldehyde and propionaldehyde the reaction Is conducted without solvent in a small, heated autoclave. With the exception of furoin the preparation of benzoins from aromatic aldehydes is best carried out with a different thiazolium catalyst bearing an N-methyl or N-ethyl substituent, instead of the N-benzyl group. Benzoins have usually been prepared by cyanide-catalyzed condensation of aromatic and heterocyclic aldehydes.Unsymnetrical acyloins may be obtained by thiazol1um-catalyzed cross-condensation of two different aldehydes. -1 The thiazolium ion-catalyzed cyclization of 1,5-dialdehydes to cyclic acyloins has been reported. 

Knabe et al. (271-274) later observed that 6,7-dimethoxy-2-methyl-1,2-dihydroisoquinolines (175), possessing either a free or a substituted benzyl group in position 1, readily rearrange to 3,4-dihydroisoquinoline salts (176) on treatment with dilute acids. 

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