PROTECTING GROUPS 57 Smith: Chapter 7
PROTECTING GROUPS 57Carey & Sundberg Chapter # 1; 2; 3a, b, c ;Smith: Chapter 7Protecting Greene & Wuts, Protective GROUPS in Organic Synthesis (2nd edition) J. Wiley & Sons, J. Kocienski, PROTECTING GROUPS , Georg Thieme Verlag, groups2Ketones and Acids- Protect functional GROUPS which may be incompatible with a set of reactionconditions- 2 step process- must be efficient- Selectivity a. selective protectionb. selective deprotectionHydroxyl PROTECTING GroupsEthersMethyl ethersR-OH R-OMedifficult to remove except for on phenolsFormation:- CH2N2, silica or HBF4- NaH, MeI, THFCleavage:- AlBr3, EtSH- PhSe -- Ph2P -- Me3SiIOOOBzOMeOOOBzOHAlBr3, EtSHTL 1987, 28 , 3659Methoxymethyl ether MOMR-OH R-OCH2OMestable to base and mild acidFormation:- MeOCH2Cl, NaH, THF- MeOCH2Cl, CH2Cl2, iPr2EtNCleavage- Me2BBr2TL 1983, 24 , 3969PROTECTING GROUPS 58Methoxyethoxymethyl ethers (MEM)R-OH R-OCH2OCH2CH2OMestable to base and mild acidFormation:- MeOCH2CH2OCH2Cl, NaH, THF- MeOCH2CH2OCH2Cl, CH2Cl2, iPr2EtNTL 1976, 809Cleavage- Lewis acids such as ZnBr2, TiCl4, Me2BBr2OC
PROTECTING GROUPS 58 Methoxyethoxymethyl ethers (MEM) R-OH → R-OCH2OCH2CH2OMe stable to base and mild acid Formation: - MeOCH2CH2OCH2Cl, NaH, THF - MeOCH2CH2OCH2Cl, CH2Cl2, iPr2EtN TL 1976, 809 Cleavage - Lewis acids such as ZnBr2, TiCl4, Me2BBr2 C 5 H 11 O MEM-O
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