Best Synthetic Methods: Functional Group Protection

• Main Author: Taber, Douglass
• Format: Book Part
• Language: unknown
• Published: Oxford University Press 2011
• Subjects: Akureyri; University of Akureyri
• Online Access: http://dx.doi.org/10.1093/oso/9780199764549.003.0012

Benzyl esters are easily deprotected by hydrogenolysis. It is often observed, however, as exemplified by the conversion of 1 to 2 reported (Adv. Synth. Catal. 2008, 350, 406) by Hironao Sajiki of Gifu Pharmacutical University, that alkene hydrogenation can be carried out selectively. Fernando Albericio of the University of Barcelona has developed (Tetrahedron Lett. 2008, 49, 3304) a family of thiophene-based esters 3 that can be removed with acid in the presence of t-butyl esters, and that are stable to the removal of FMOC groups. Vassiliki Theodorou of the University of Ioannina has found (Tetrahedron Lett. 2008, 49, 8230) that esters were rapidly saponified by methanolic NaOH in solvent CH2Cl2. Specific oligosaccharide synthesis depends heavily on the use of orthogonal methods for alcohol protection and deprotection. This is illustrated by the work (J. Org. Chem. 2008, 73, 1008) of Carolyn R. Bertozzi of the University of California, Berkeley, who deployed p-methoxybenzyl (PMB), 3,4-dimethoxybenzyl (DMB), p-chlorobenzyl (PCB) and p-iodobenzyl (PIB) ethers to enable construction of a disaccharide, by way of 9. Piers R. J. Gaffney of Imperial College London has reported (Tetrahedron Lett. 2008, 49, 1836) a practical preparation of the ether 11, that should make this symmetrical protecting group more readily available. George W. J. Fleet of the University of Oxford and Sigthur Petursson of the University of Akureyri have found (Tetrahedron Lett. 2008, 49, 2196) that diphenyl diazomethane 14, easily prepared from benzophenone, reacted under neutral conditions with primary, secondary and tertiary alcohols to form the benzyhydryl ethers. Harsh conditions have often been employed to remove aryl methyl ethers such as 16. Wei Wang of the University of New Mexico and Wenhu Duan of the Shanghai Institute of Materia Medica have developed (Tetrahedron Lett. 2008, 49, 4054) a simple protocol to effect this transformation, by heating the ether to reflux in DMF in the presence of iodocyclohexane 17. Dithianes such as 19 have ...