Ethers methoxy methyl

By careful optimization, Widdowson and coworkers were able to show that methoxy-methyl ethers of phenols are better substrates for alkyllithium-diamine controlled enan-tioselective deprotonation, and (—)-sparteine 362 is then also the best ligand among those surveyed the BuLi-(—)-sparteine complex deprotonates 447 to give, after electrophilic quench, compounds such as 449 in 58% yield and 92% ee (Scheme 180) . Deprotonation of the anisole complex 410 (see Scheme 169) under these conditions gave products of opposite absolute stereochemistry with poor ee. 

Reaction of R2CuLi with sec-tosylates.1 Displacement of tosyloxy groups is facilitated by the presence of S or O atoms in the vicinity. In the case of methoxy-methyl ethers or (methylthio)methyl ethers, optimum conditions obtain when the S or O atoms are in a vicinal position. This reaction is useful because it involves complete inversion of configuration. As shown by the last entry in equation (I), the yield of the substitution is low if a heteroatom is absent. A sulfur atom is more effective than oxygen for coordination to copper. 

Directed metallation SEM ethers of phenols are as useful as MOM (methoxy-methyl) ethers for directed ort/io-metallation of aromatic systems, and have the added advantage of removal by fluoride ion. This group is also useful for directed lithiation of hydroxypyridines. 

The allylmetallation of vinyl metals, y-heterosubstituted with a methoxy-methyl ether as the chelating group, leads to the corresponding gembismetal-lic derivatives,20 but now, warming the reaction mixture to room temperature promotes an internal nucleophilic substitution, leading to a metallated cyclopropane which can react with different electrophiles21 (Equation 7.5 and Protocol 9). 

Deprotection of MEM and MOM ethers. Methoxyethoxymethyl and methoxy-methyl ethers are cleaved to the alcohol by this reagent in high yields. Either 2-butanone or 2-methyl-2-propanol is recommended as solvent. The procedure is particularly useful for cleavage of ethers of allylic alcohols, for which ZnBr, and TiCh are not useful. 

When the intramolecular chelating group see Chelating Ligands) is a methoxy-methyl-ether (MOM) in y-position, an... 

Alkoxymethyl Ethers The principal members of this set of protecting groups are methoxy-methyl ether (MOM) [188], methoxyethoxymethyl ether (MEM) [189], benzyloxymethyl ether (BOM) [190], /7-methoxybenzyloxymethyl ether (PMBM) [191], and trimethylsi-lylethoxymethyl ether (SEM) [192] (O Fig. 4). Since these protecting units are devoid of chirality, their use introduces no stereochemical complications. 

Amberlyst-15 was also used as a catalyst for the reaction of alcohols and phenols with tetrahydropyran (Eqn. 22.33). Refluxing a mixture of an alcohol and dimethoxymethane in the presence of a Nafion-H catalyst gave the methoxy methyl ethers in very good yields (Eqn. 22.34). ° Nafion-H was also used to catalyze the conversion of diols to cyclic ethers. ... 

Aplysin and ( ) debromo aplysin have been prepared from wemcresyl methoxy methyl ethers... 

Methoxymethyl ethers of phenols. Phenols can be converted into methoxy-methyl ethers (Ar0CH20CH3> in 80-95% yield by reaction with chloromethyl methyl ether under phase-transfer conditions. Adogen 464 (6, 10) has been used as catalyst. 

The formation of a cyclopropane by 1,3-elimination between an organogembismetallic and a methoxy-methyl ether was already described (a) Marek I, Beruben D, Normant JF (1995) Tetrahedron Lett 36 3695 (b) Beruben D, Marek I, Normant JF, Platzer N (1995) J Org Chem 60 2488 (c) Beruben D, Marek I, Normant JF, Platzer N (1993) Tetrahedron Lett... 

In 2005, Fagnou achieved the formal synthesis of (—)-allocolchicine through a palladium-catalyzed intramolecular C-H/C-X coupling [411]. The intramolecular biaryl coupling of 1,3-diarylpropane precursor 40 proceeded in the presence of Pd(OAc)2> DavePhos (41), and K2CO3 at 145 °C to furnish the seven-membered ring in 42. Deprotection of the methoxy methyl ether (MOM) group by HCl, followed by... 

Fig. 3 Effect of cholesteryl ethers in liposomes prepared with DOPC on the relative amount of glucose released (A) (x) cholesterol (o) cholesteryl methyl ether ( ) cholesteryl ethyl ether (v) cholesteryl-n-propyl ether ( ) cholesteryl isopropyl ether (A) cholesteryl butyl ether (B) (x) cholesterol (o) cholesteryl (2 -hydroxy)-3-ethyl ether ( ) cholesteryl methoxy methyl ether ( ) cholesteryl acetate.

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