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Protection hydroxy groups

Ethyl vinyl ether is also useful for hydroxy group protection. The resulting derivative (1-ethoxyethyl ether) is abbreviated as the EE group.156 As with the THP group, the EE group introduces an additional stereogenic center. [Pg.260]

The phosphonium salt is more acidic than usual because its conjugate base, the ylide, is stabilized by resonance involving the double bonds. Therefore, methoxide ion, a weaker base than usual, can be used lo form the ylide. Reaction of the ylide with the aldehyde that has its hydroxy group protected as an ester produces vitamin A acetate. The acetate group can readily be removed to complete the synthesis of vitamin A (see Section 10.2). [Pg.764]

JCS(C)2094). In the thiazolopyrimidine (382) the hydroxy group protects the pyrimidine ring, and it is the thiazole ring which is cleaved with loss of C-2 (70JCS(C)2478). [Pg.689]

The intramolecular 1,4-conjugate addition can be accomplished starting from a hydroxy group protected as silyl ether. The cyclization of the enone 13, however, performed by treatment with tetrabutylammonium fluoride in refluxing tetrahydrofuran, gives the 2,6-fra/t.s-tetrahydropy-ran 14 in only 11 % yield160. [Pg.306]

Furthermore, superhydride is used as an alternative to LAH in the reduction of carbohydrate epoxides (equation 18), In this example, the C—O bond away from the hydroxy group is selectively cleaved, but a tosyloxy group is also reduced in epoxides having a hydroxy group protected with tosyl. A kinetic study of reductions with superhydride has been reported. ... [Pg.875]

Tetrahydrofuranyl (THF) ethers are reported to be useful alternatives to tetrahydropyranyl (THP) ethers for the protection of alcohols (and thiols). THF ethers are easily formed, and are more sensitive to acidic hydrolysis than are THP ethers. We are warned that hydroboration-oxidation or peracid oxidation of simple unsaturated compounds containing a hydroxy-group protected as its THP ether has led to violent detonations. The danger comes from the ready formation of peroxides from THP ethers, and presumably also from THF ethers these peroxides, though very sensitive, are not easily removed by ordinary chemical methods. [Pg.243]

Oxidation of carbohydrate deriratwes. Oxidation of partially acetylated carbohydrates with the reagent of Parikh and Doering leads to both oxidation and elimination of the elements of acetic acid, and thus provides a high-yield route to novel unsaturated carbohydrates.3 Apparently the oxidation step is followed by spontaneous elimination of a /f-acctoxy group. Hydroxy groups protected by benzyl or trimethylsilyl groups are not eliminated. [Pg.438]

An alternative synthesis of five-membered cyclic nitrones such as 763 differs from the previous one in the choice of substrates for hydroxy group protection and pyrrolidine ring formation. Lithium aluminum hydride reduction of 766a-c followed by tosylation affords the ditosylate 767 in good yield. These threitols are cyclized to the A-hydroxypyrrolidines 768 with hydroxylamine in refluxing ethanol. Oxidation of 768 with yellow mercury(II) oxide in dichloromethane affords the nitrones 769 in quantitative yield. This methodology avoids the... [Pg.437]

The 3(S)-hydroxybutanoate 141 obtained by bakers yeast reduction of ethyl acetoacetate was the starting material providing the required chirality at C37 (Scheme 18). Stereoselective alkylation, hydroxy group protection, and aldehyde formation at C35 gave the anti-product 142. Aldol condensation with vinylbor-... [Pg.161]

Full details of the reductive deamination of amino-sugars by the sequence shown in Scheme 1 have been reported. It is usually necessary to have hydroxy-groups protected by acetylation and in this way 2-deoxy-Q - and -P-D-arabino-hexose tetra-acetates can be made in high overall yields. The reaction has been applied to the neamine derivative (2) with which the reaction proceeds in a stepwise fashion allowing mono-, di-, tri-, and tetra-deoxy derivatives to be isolated. The order of reduction is indicated on the structure (2). ... [Pg.100]


See other pages where Protection hydroxy groups is mentioned: [Pg.150]    [Pg.166]    [Pg.458]    [Pg.175]    [Pg.228]    [Pg.228]    [Pg.201]    [Pg.363]    [Pg.700]    [Pg.919]    [Pg.125]    [Pg.688]    [Pg.236]    [Pg.147]    [Pg.156]    [Pg.161]    [Pg.162]    [Pg.163]    [Pg.169]    [Pg.228]    [Pg.220]    [Pg.168]    [Pg.536]    [Pg.365]   
See also in sourсe #XX -- [ Pg.761 ]




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