Benzyl alcohols reaction with phosgene

SYNTHESIS The first step involves the s)mthesis of the amino acid 7-benzyl-L-glutamate by a standard Fischer esterification reaction of L-glutamic acid with benzyl alcohol in the presence of strong acid. The amino acid is subsequently converted to the N-carboxyanhydride (NCA) monomer by reaction with phosgene gas, or by reaction with the less hazardous compound triphosgene.The NCA is polymerized by initiation with a variety compounds such as primary and secondary amines, and alkoxides. Typical comonomers include other amino acid NCAs. 

Figure 6.28 shows the SN reaction of two equivalents of benzyl alcohol (formula B) with C13C—O—C(=0)—Cl (diphosgene, formula C preparation Section 1.7.1). It is preferable to work with diphosgene, which is a liquid, rather than with phosgene... 

The reaction of phosgene with benzyl alcohol yields benzyl chloroformate (carbobenzoxy chloride), CICO2CH2C6H5, useful in protecting (Ege, 1999) amino groups of amino acids. (Deprotection is accomplished with H2/Pd/C.)... 

Thus, the chloroformates of primary and secondary alcohols, prepared by reaction of the alcohol with phosgene, are reduced to the corresponding alkane in excellent yield on reaction with tri-n-propylsilane in the presence of t-butyl peroxide at 140 °C yields are low for aryl and benzyl alcohols. A method for the direct replacement of the hydroxy-group of alcohols by alkyl or aryl groups has been described (see Scheme 11, ref. 67). 

Carbobenzoxy function (CBz) is also an acyl protecting group for the amino function which is removed by hydrogenolysis or under acidic conditions. The chloride is prepared by reaction of benzyl alcohol with phosgene ... 

Preparative Methods CbzCl can be readily prepared by the reaction of benzyl alcohol and phosgene, either in toluene solution or neat. Purification of such freshly prepared CbzCl is often not necessary indeed, ca. 25% residual toluene solvent does not interfere with derivatization reactions. ... 

Some routes leading to transformation of carbanions into cations were described4585. One of the methods involves capping carbanions with bromine and conversion via Grig-nard into reactive benzyl bromides that could be oxidized by silver salts. Alternatively, phosgene could be used as the reagent4595. Conversion of cations into anions is exemplified by the reaction of living polytetrahydrofuran with lithium salt of cinamyl alcohol,... 

Benzyl esters of a-amino acids may be formed by reaction of the alcohol with the cyclic anhydride (12) formed between the amino acids and phosgene [37]. 

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