Methoxymethyl MOM

Protection of ethyl L-lactate with a MOM group (377) can be effected in high yield with either chloromethyl methyl ether in the presence of Hunig s base [100,119] or with dimethoxy-methane and phosphorus pentoxide [120]. 

Inverse addition of the dianion generated from 380 to lactate 379 results in a 2 1 mixture of diastereomers 381 and 382. After separation of the mixture by column chromatography, the major diastereomer 381 is lactonized by acidic removal of the MOM group. 

A related family of 3-amino-2,3,6-trideoxyhexoses, L-daunosamine (386), the carbohydrate component of anticancer anthracycline antibiotics, L-vancosamine (387), the carbohydrate component of the antibiotics vancomycin and sporaviridin, and D-ritosamine (388), the enantiomer of the carbohydrate component of the antibiotic ristomycin, has been prepared from ethyl L-lactate [119]. 

The oxazole ring is readily cleaved with 10% HCI, which also removes the MOM group, and quantitatively gives 3-amino-5-methyltetronic acid. Hydrogenation of the Boc-protected 

Conversion of 393 to L-daunosamine (386) is accomplished by reduction of the lactone to lactol 394 followed by a Wittig reaction and acid hydrolysis with 20% HCl—THF (1 1.7) 

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Bromocatecholborane. Ethyl esters are not affected by this reagent, but it does cleave other groups see the section on methoxymethyl (MOM) ethers. 

The construction of the five contiguous stereocenters required for a synthesis of compound 3 is now complete you will note that all of the substituents in compound 5 are positioned correctly with respect to the carbon backbone. From intermediate 5, the completion of the synthesis of the left-wing sector 3 requires only a few functional group manipulations. Selective protection of the primary hydroxyl group in 5 as the corresponding methoxymethyl (MOM) ether, followed by benzylation of the remaining secondary hydroxyl, provides intermediate 30 in 68 % overall yield. It was anticipated all along that the furan nucleus could serve as a stable substi-... 

The methoxymethyl (MOM) and (3-methoxyethoxymethyl (MEM) groups are used to protect alcohols and phenols as formaldehyde acetals. These groups are normally introduced by reaction of an alkali metal salt of the alcohol with methoxymethyl chloride or (3-methoxyethoxymethyl chloride.157... 

Chloromethyl ethers.1 BC1, cleaves methoxymethyl (MOM) ethers to give chloromethyl ethers. 

Alkoxy ketones. These ketones can be prepared by an aldol-type reaction of enol ethers with acetals catalyzed by a trityl salt. Methoxymethyl (MOM) enol ethers are more reactive than methyl enol ethers. 

A straightforward synthesis (Scheme 3) of a furocoumarin-thymidine furan-side adduct was developed <1997JOC2630>. The methoxymethyl (MOM)-protecting group in 33 was removed in 91% yield with ethanolic HCl, and the resulting phenol 34 was condensed with dimethylacetamide dimethyl acetal in the presence of 4 A... 

When the t -butyl group in 78 is replaced by a methoxymethyl (MOM) group, the dimetallic intermediate 80 undergoes a 1,3-elimination to give a cyclopropane 82 (equation 36)46. 

Methylthio)methyl ethers (MTM ethers, ROCH2SCH3).1 Methoxymethyl (MOM) and (2-methoxyethoxy)methyl (MEM) ethers are converted to MTM ethers by reaction with (CH3)2BBr in CH2C12 at -78° for 1 hour followed by reaction with... 

Aldehydes may be readily oxidized giving carboxylic acids in very good yield. This reaction has recently been performed using sodium perchlorate in aqueous acetonitrile (equation 44)182. Aldehydes may also be converted into methoxymethyl (MOM) esters, an interesting synthetic sequence that involves the initial formation of an organostanane followed by oxidation with ozone at —78°C (equation 45)183. The a-alkoxyesters produced in this later reaction seem to be potentially very useful synthons for further synthetic elaboration. 

Very recently, a research group at the Sloan-Kettering Memorial Cancer Center reported a new approach to 5-deazaAP (80a), 5-deaza-5-methylAP (124) and 5-deaza-5-methylFA (126)[90, 91]. As an extension of their novel pyrimidine-to-pyridopyrimidine ring transformation [92] this strategy required four key steps - the pyrimidine-to-pyridopyrimidine ring transformation, removal of the 7-amino group, deprotection of the 1,3-A-methoxymethyl (MOM) substituents, and conversion of the resulting 2,4-dioxo derivative to the... 

A methoxymethyl [MOM] protecting group at C-2 could not be removed following esterification ... 

A methoxymethyl (MOM) protecting group at N-3 was chosen based on its successful use in the total synthesis of nucleoside Q.31 Our previous experience with the total synthesis of rigidin vide supra) suggested BOM protection for the N-1 position and a 2,4-dimethoxybenzyl (DMB)... 

Thus the hypothesis in Figure 3.4 is indeed effective for designing asymmetric synthesis. However, the main drawbacks in the transformation of 32 into 33 are low chemical yield and difficulty in removing the (V-mcthyl protective group. Further investigation of other (readily removable) nitrogen substituents and conditions for asymmetric induction are shown in Table 3.4. The best result was obtained with A-methoxymethyl(MOM)-A-Boc derivative 40. Treatment of 40 with KHMDS in toluene-THF (4 1) at —78°C for 30 minutes followed by the addition of methyl iodide afforded 41 in 96% yield and 81% ee (entry 9).27,28 Use of a toluene-THF (4 1) mixture as a solvent is crucial for both high yield and enantioselectivity (entries 7-9). 

Protection of tertiary alcohols. Methylthidiiiethyl (MTM) ethers have the advantage that they can be prepared from tertiary alcolols (7,135), but the disadvantage that they are prone to oxidation. They can be convcrtcil into 2-mcthoxycthoxymethyl (MEM) ethers, methoxymethyl (MOM) ethers, or ethoxy methyl (EOM) ethers by reaction with... 

Cyanomethyl ethers.l Methoxyethoxymethyl (MEM) ethers are converted into cy-anomethyl ethers by reaction with excess diethylaluminum cyanide in toluene at 100° (equation I). The same reaction with methoxymethyl (MOM) ethers is considerably slower. 

Cleavage of ethers1 and acetals.2 This reagent cleaves cyclic and acyclic acetals and ketals, including p-methoxyethoxymethyl (MEM), methoxymethyl (MOM), and... 

Walker et al prepared lOa-spiro epoxide (42a) and its 7-methoxymethyl (MOM) ether (42b), which exhibited comparable cytotoxicity and tubulin assembly activity with paclitaxel. 

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