Photoremovable Protecting Groups in Organic Synthesis

The applications of light-sensitive protecting groups which can be removed by photolysis in the synthesis of organic compounds are reviewed. The use of groups such as 2-nitrobenzyl, benzyloxycarbonyl, 3-nitrophenyl, phenacyl, 3,5-dimethoxybenzoinyl, and 2, 4-dinitrobenzenesulphenyl for the blocking of various functional groups is reviewed with particular emphasis on their application in syntheses involving polyfunctional molecules. The methods for the incorporation of the protecting group, subsequent synthetic steps, and the final removal of the employed protecting group are illustrated with specific examples. The important applications of these groups in carbohydrate chemistry, nucleotide synthesis, and peptide synthesis on polymeric supports are discussed. 1. Introduction 2. 2-Nitrobenzyl and Related Groups 2.1. 2-Nitrobenzyl and α-Substituted 2-Nitrobenzyl Groups 2.2. 2-Nitrobenzyloxycarbonyl and α-Substituted 2-Nitrobenzyloxycarbonyl Groups 2.3. 2-Nitrophenylethyleneglycol Group 3. Benzyloxycarbonyl and Related Groups 3.1. Benzyloxycarbonyl Group 3.2. 3,5-Dimethoxybenzyloxycarbonyl Group 3.3. α,α-Dimethyl-3,5-dimethoxybenzyloxycarbonyl Group 4. 3-Nitrobenzyl and Related Groups 4.1. 3-Nitrophenyloxy and 3,5-Dinitrophenyloxy Groups 4.2. 3-Nitrophenyloxycarbonyl Group 5. Phenacyl Groups 5.1. 4-Methoxyphenacyl Group 5.2. α-Methylphenacyl Group 6. 3,5-Dimethoxybenzoinyl Groups 7. 2,4-Dinitrobenzenesulphenyl Group 8. Other Miscellaneous Groups 9. Specific Applications 9.1. Carbohydrate Synthesis 9.2. Nucleotide Synthesis 9.3. Polymer-Based Peptide Synthesis 10. Conclusions