Ethers benzyl, reaction with

Reactions of the Side Chain. Benzyl chloride is hydrolyzed slowly by boiling water and more rapidly at elevated temperature and pressure in the presence of alkaHes (11). Reaction with aqueous sodium cyanide, preferably in the presence of a quaternary ammonium chloride, produces phenylacetonitrile [140-29-4] in high yield (12). The presence of a lower molecular-weight alcohol gives faster rates and higher yields. In the presence of suitable catalysts benzyl chloride reacts with carbon monoxide to produce phenylacetic acid [103-82-2] (13—15). With different catalyst systems in the presence of calcium hydroxide, double carbonylation to phenylpymvic acid [156-06-9] occurs (16). Benzyl esters are formed by heating benzyl chloride with the sodium salts of acids benzyl ethers by reaction with sodium alkoxides. The ease of ether formation is improved by the use of phase-transfer catalysts (17) (see Catalysis, phase-thansfer). 

Conversion of phenols into their methyl or ethyl ethers by reaction with the corresponding alkyl sulphates in the presence of aqueous sodium hydroxide affords a method which avoids the use of the more expensive alkyl halides (e.g. the synthesis of methyl 2-naphthyl ether and veratraldehyde, Expt 6.111). Also included in Expt 6.111 is a general procedure for the alkylation of phenols under PTC conditions.38,39 The method is suitable for 2,6-dialkylphenols, naphthols and various functionally substituted phenols. The alkylating agents include dimethyl sulphate, diethyl sulphate, methyl iodide, allyl bromide, epichlorohy-drin, butyl bromide and benzyl chloride. 

Methyl 2,3-di-0-benzyl-oc-D-glucopyranoside gives 58% of 2,3,6- and 21% of 2,3,4-tri-0-benzyl ether on reaction with 1.4 equiv. of sodium hydride and benzyl bromide [71]. In a remarkably selective reaction, 62% of methyl 2,4,6-tri-0-benzyl-a-D-glucopyranoside result from the unprotected methyl a-D-glucopyranoside [74]. Benzyl chloride has been used for this transformation, as well as for the efficient synthesis of methyl 2,4-di-0-benzyl-a-D-xylopyranoside [75] 1 As expected, OH-2 in methyl 4,6-0-benzylidene-a-D-glucopyranoside is more reactive [71] than OH-3. 

Treatment of oestrone with tetraphenylbismuth monotrifluoroacetate gave oestrone phenyl ether and exemplified, in part, a new procedure for aryl ether formation.31 A detailed study was reported of the formation of benzyl ethers by sequential reaction of alcohols with chloro(phenylmethylene)dimethylammonium chloride and sodium hydrogen telluride.32 Steroidal alcohols, inter alia, were converted into hydrolytically stable silyl ethers by reaction with B N Sil or BulPh2I which were generated in situ from the selenosilane and iodine.33 The 5a-hydroxycholestane (21) was protected in this way. 

Preparation of the chiral oxazolidine-aldehyde 64 from D-serine 59 required various steps, including conversion into the silyl ether 60, reaction with ketone 61 to provide oxazolidine silyl ether 62 and subsequent desilylation of the tert-butyldiphenylsiloxy group. Oxidation of the hydroxy functionality and hydrogeno-lytic cleavage of the benzyl ester then gave the corresponding aldehyde 63. The acid functionality of 63 was then coupled to aminomethylated Merrifield resin (Scheme 12.26). 

The sequence starts out with the protection the hydroxyl group at C17 as its benzyl ether by reaction with benzyl chloride in the presence of base such as sodium carbonate (27-2). Treatment of a solution of the benzyl ether in acetic acid with / -toluenesulfonic acid causes the styrenoid bond to shift from the B-C ring fusion to the more transoid, and presumably more stable, 9,11-position. This now provides a means for activating Cn. Hydroboration with diborane... 

Certain benzyl sulfides are converted to the benzyl methyl ethers by reaction with thallium(III) nitrate in methanol (21). The soft donor characteristic of thiocarbonyl and selenocarbonyl groups has been exploited in the replacement of hydroxy functions with halogen atoms (22). Thus, xanthates and thiobenzoates are activated by alkyl halides. 

Ph.CH2.OMe, Ph.(CH2)2.0Me, Ph.(CH2)3.0Me (2-3, 3-4, 1-3), does not decrease steadily, but goes through a maximum. These two circumstances point to a specific -interaction in nitrations of the ethers with acetyl nitrate which is important with benzyl methyl ether, more important with methyl phenethyl ether, and not important with methyl phenpropyl ether. This interaction is the reaction with dinitrogen pentoxide already mentioned, and the variation in its importance is thought to be due to the different sizes of the rings formed in the transition states from the different ethers. 

Quantitative Analysis of All llithium Initiator Solutions. Solutions of alkyUithium compounds frequentiy show turbidity associated with the formation of lithium alkoxides by oxidation reactions or lithium hydroxide by reaction with moisture. Although these species contribute to the total basicity of the solution as determined by simple acid titration, they do not react with allyhc and henzylic chlorides or ethylene dibromide rapidly in ether solvents. This difference is the basis for the double titration method of determining the amount of active carbon-bound lithium reagent in a given sample (55,56). Thus the amount of carbon-bound lithium is calculated from the difference between the total amount of base determined by acid titration and the amount of base remaining after the solution reacts with either benzyl chloride, allyl chloride, or ethylene dibromide. 

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). 

SuIfona.tlon, Sulfonation is a common reaction with dialkyl sulfates, either by slow decomposition on heating with the release of SO or by attack at the sulfur end of the O—S bond (63). Reaction products are usually the dimethyl ether, methanol, sulfonic acid, and methyl sulfonates, corresponding to both routes. Reactive aromatics are commonly those with higher reactivity to electrophilic substitution at temperatures > 100° C. Tn phenylamine, diphenylmethylamine, anisole, and diphenyl ether exhibit ring sulfonation at 150—160°C, 140°C, 155—160°C, and 180—190°C, respectively, but diphenyl ketone and benzyl methyl ether do not react up to 190°C. Diphenyl amine methylates and then sulfonates. Catalysis of sulfonation of anthraquinone by dimethyl sulfate occurs with thaHium(III) oxide or mercury(II) oxide at 170°C. Alkyl interchange also gives sulfation. 

Benzyl chloride readily forms a Grignard compound by reaction with magnesium in ether with the concomitant formation of substantial coupling product, 1,2-diphenylethane [103-29-7]. Benzyl chloride is oxidized first to benzaldehyde [100-52-7] and then to benzoic acid. Nitric acid oxidizes directly to benzoic acid [65-85-0]. Reaction with ethylene oxide produces the benzyl chlorohydrin ether, CgH CH20CH2CH2Cl (18). Benzylphosphonic acid [10542-07-1] is formed from the reaction of benzyl chloride and triethyl phosphite followed by hydrolysis (19). 

A -Dieiiol ethers are also formed by acid-catalyzed reaction of the steroid directly with benzyl alcohol with azeotropic removal of water/ Use of isooctane as azeotropic carrier may improve yields/ ... 

Benzyl ethers of phenols can also be prepared by reaction with phenyldi-azomethane. 

The thenyl chlorides appear to be more reactive in nucleophilic aliphatic substitution than the benzyl analogs. Thus, 2-thenyh chloride gives, in the reaction with sodium cyanide in ethanol, a mixture of ethyl 2-thenyl ether (25% yield) and 2-thenyl cyanide (32% yield), whereas benzyl chloride gives a high 3deld of benzyl cyanide uncontaminated with benzyl ether. When 2-thenyl chloride and benzyl chloride were allowed to compete for a deficiency of sodium amyloxide, 2-thenyl chloride reacted three times faster. In acetone solution 2-thenyl cyanide is obtained smoothl. ... 

Hydrogenolysis (Section 26.7) Cleavage of a bond by reaction with hydrogen. Benzylic ethers and esters, for instance, are cleaved by hydrogenolysis. 

With the iodine atom in its proper place, provisions for construction of the C9-C10 bond by an aldol reaction could be made (see Scheme 44). To this end, oxidative cleavage of the para-methoxy-benzyl ether in 181 with 2,3-dichloro-5,6-dicyano-l,4-benzoqui-none (DDQ) in CH2CI2-H2O furnishes a primary alcohol that can... 

With ring G in place, the construction of key intermediate 105 requires only a few functional group manipulations. To this end, benzylation of the free secondary hydroxyl group in 136, followed sequentially by hydroboration/oxidation and benzylation reactions, affords compound 137 in 75% overall yield. Acid-induced solvolysis of the benzylidene acetal in 137 in methanol furnishes a diol (138) the hydroxy groups of which can be easily differentiated. Although the action of 2.5 equivalents of tert-butyldimethylsilyl chloride on compound 138 produces a bis(silyl ether), it was found that the primary TBS ether can be cleaved selectively on treatment with a catalytic amount of CSA in MeOH at 0 °C. Finally, oxidation of the resulting primary alcohol using the Swem procedure furnishes key intermediate 105 (81 % yield from 138). 

The outcomes of intramolecular cyclizations of hydroxy vinylepoxides in more complicated systems can be difficult to predict. In a study of the synthesis of the JKLM ring fragment of dguatoxin, epoxide 44 was prepared and subjected to acid-mediated cydization conditions (Scheme 9.24) [114]. Somewhat surprisingly, the expected oxepane 45 was not formed, but instead a mixture of tetrahydropyran 46 and tetrahydrofuran 47 was obtained, both compounds products of attack of the C6 and C5 benzyl ether oxygens, respectively, on the allylic oxirane position (C3). Repetition of the reaction with dimsylpotassium gave a low yield of the desired 45 along with considerable amounts of tetrahydropyran 48. 

Rhodium catalysts have also been used. Benzylic halides were converted to carboxylic esters with CO in the presence of a rhodium complex. In this case, the R could come from an ether R20, a borate ester B(OR )3, or an Al, Ti, or Zr alkoxide. Reaction with an a,co-diiodide, BU4NF and Mo(CO)e gave the corresponding lactone. ... 

Alkyl esters are efficiently dealkylated to trimethylsilyl esters with high concentrations of iodotrimethylsilane either in chloroform or sulfolane solutions at 25-80° or without solvent at 100-110°.Hydrolysis of the trimethylsilyl esters serves to release the carboxylic acid. Amines may be recovered from O-methyl, O-ethyl, and O-benzyl carbamates after reaction with iodotrimethylsilane in chloroform or sulfolane at 50—60° and subsequent methanolysis. The conversion of dimethyl, diethyl, and ethylene acetals and ketals to the parent aldehydes and ketones under aprotic conditions has been accomplished with this reagent. The reactions of alcohols (or the corresponding trimethylsilyl ethers) and aldehydes with iodotrimethylsilane give alkyl iodides and a-iodosilyl ethers,respectively. lodomethyl methyl ether is obtained from cleavage of dimethoxymethane with iodotrimethylsilane. 

The use of iodotrimethylsilane for this purpose provides an effective alternative to known methods. Thus the reaction of primary and secondary methyl ethers with iodotrimethylsilane in chloroform or acetonitrile at 25—60° for 2—64 hours affords the corresponding trimethylsilyl ethers in high yield. The alcohols may be liberated from the trimethylsilyl ethers by methanolysis. The mechanism of the ether cleavage is presumed to involve initial formation of a trimethylsilyl oxonium ion which is converted to the silyl ether by nucleophilic attack of iodide at the methyl group. tert-Butyl, trityl, and benzyl ethers of primary and secondary alcohols are rapidly converted to trimethylsilyl ethers by the action of iodotrimethylsilane, probably via heterolysis of silyl oxonium ion intermediates. The cleavage of aryl methyl ethers to aryl trimethylsilyl ethers may also be effected more slowly by reaction with iodotrimethylsilane at 25—50° in chloroform or sulfolane for 12-125 hours, with iodotrimethylsilane at 100—110° in the absence of solvent, " and with iodotrimethylsilane generated in situ from iodine and trimcthylphenylsilane at 100°. ... 

N -Fmoc serine benzyl ester 2, which could be prepared as shown or purchased commercially, was smoothly converted to the crystalHne O-methylthiomethyl (MTM) ether 3 in high yield via a Pummerer-Hke reaction using benzoyl peroxide and dimethyl sulfide in acetonitrile [39]. This common intermediate was used to synthesize both 5 and 8 [40]. Both Ogilvie [41] and Tsantrizos [42] had reported that I2 was an effective activator with similar MTM ether substrates. The H promoted nucleosidation reaction between O-MTM ether 3 and bis-silylated thymine 4 produced the nucleoamino acid 5 in 60% isolated yield (100% based on recovered 3). Hydrogenolytic deprotection of the benzyl ester with H2, Pd/C in MeOH gave the thymine-containing nucleoamino acid 6 in quantitative yield. 

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