Methoxyethoxy methyl MEM

Protection of ethyl L-lactate with a MEM group is easily accomplished by alkylation with (2-methoxyethoxy)methyl chloride in the presence of Hunig s base (2- 372) [100,116,117]. 

The protecting group can be removed under mild conditions by treating 372 with one equivalent of catechol boron bromide [118]. This reagent is also effective for cleaving other protecting groups, such as /er/-butyl, allyl, benzyl or MOM ethers, as well as N-Cbz and N-Boc functionalities. 

The chelative ability of the oxygen atoms in the MEM group results in an ideal environment for the addition of organolithium reagents to the ester group of 372. If the reaction is performed at —100 °C in ether/pentane (1 1) for a maximum of 10 min, protected a-hydroxyketones 374 are produced, with only minor amounts of alcohol 375 appearing [5]. At temperatures below — 80 °C the intermediate 373 is sufficiently stable to prevent in situ formation of 374, which upon further addition of RLi is responsible for production of the undesired alcohol 375. 

The identical reaction based on a MOM-protected lactate, which contains one less oxygen, produces a 3 1 mixture of a-hydroxyketone/alcohol with only 56—58% ee. 

A superior method for effecting the transformation is to use lactamide 376 instead of ester 372. In this case the reaction is performed in THF/ether (7 3) at 5 °C and within 1 product 374 is formed in 80% yield with an enantiomeric excess of 99%. 

---

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... 

Hydroxybenzyl alcohols have been converted to dioxepins, as the major product, by forming methoxyethoxy-methyl (MEM) ethers either on the phenolic -OH or on the benzylic -OH and reacting the other -OH group with bromoacetaldehyde dimethyl acetal, followed by treatment with BF3-OEt2 (Scheme 9) <2004T11453>. 

Acetal esters such as methoxymethyl (Mom),P9 (2-methoxyethoxy)methyl (Mem),t l benzyloxymethyl (Bom),P l tetrahydropyranyl,P l 2-(trimethylsilyl)ethoxymethyl (SEM)t l and (methylsulfanyl)methyl (hltm) are sensitive to noild aqueous acids in THE as well as to mild Lewis acids such as magnesium bromide in diethyl ether (2 equiv, rt, l-24h).t l In addition. Bom esters may be cleaved by catalytic hydrogenation.P l In the absence of acid, acetal esters display reactivities typical for unhindered alkyl esters. Surprisingly, these esters... 

Cleavage of Acetals. Cyclic and acyclic acetals react with Mc2BBr at -78 °C to generate the parent aldehydes and ketones in excellent yield (e.g. eq 6). Primary, secondary, and tertiary (2-methoxyethoxy)methyl (MEM), methoxymethyl (MOM), and (rnethylthio)methyl (MTM) ethers also react at —78 °C to give, after aqueous workup, the corresponding alcohol. It is interesting to note that even tertiary MEM ethers cleanly regenerate the... 

Fmoc HMPA Ipc KHMDS LDA MCPBA MEM Mes MOM MS- NBS NCS NIS (+)-NLE PCC PDC Ph3P Pht PMB PNB europium 9-fluorenylmethoxycarbonyl hexamethylphosphoric triamide isopinocamphenyl potassium hexamethyldisilazanide lithium diisopropylamide 3- chloroperoxybenzoic acid (2-methoxyethoxy)methyl mesityl methoxymethyl molecular sieves iV-bromosuccinimide iV-chlorosuccinimide iV-iodosuccinimide positive non linear effect pyridinium chlorochromate pyridinium dichromate triphenylphosphane phthaloyl 4- methoxyphenyl 4-nitrobenzyl... 

MALDI-TOF Matrix assisted laser desorption ionization-time of flight MEM methoxyethoxy methyl... 

Triglycol monomethyl ether 2-(2-Methoxyethoxy) ethyl acetate. See Diethylene glycol methyl ether acetate 2-Methoxyethoxymethyl chloride CAS 3970-21-6 EINECS/ELINCS 223-589-8 Synonyms MEM-chloride p-Methoxyethoxymethyl chloride Empirical C4H9CIO2... 

---