Zinc Chloride protection/deprotection

Nitrophenyl-a-L-fuco/galacto/rhamno/manno-pyranosides can be made by the reaction of the acetate protected sugar with p-nitrophenol and zinc chloride at 120 °C under vacuum [7]. p-Nitrophenyl-p-D-gluco/galactopyranoside can be generated from the reaction of the acetylated hexopyranosyl bromides with sodium p-nitrophenoxide in DMF [8], followed by deprotection, and /7-nitrophenyl-(3-D-mannopyranoside can be synthesised from mannose via 2,3 4,6-di-0-cyclohex-ylidene-a-D-mannopyranose [9]. 

The sulphonyl chloride 23 is proposed as a protecting group for the Gabriel synthesis of secondary amines from primary amines. At the deprotecting stage, carbon-sulphur bond cleavage is achieved using zinc and acid as the electron source [109]. 

Protection and Deprotection.—In a substantial paper, Barton and co-workers have discussed in detail the protection of carboxylic acid functions in penicillin derivatives by conversion into the corresponding acylhydrazines, acylhydrazones, and dihydro-heteroaromatic amides. An alternative method for the methoxymethyl-ation of free acids, which avoids the use of toxic chloromethyl methyl ether, is by prior conversion into the zinc bromide salt followed by reaction with acetyl chloride and methylaP (Scheme 14). 

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