Methoxymethyl MOM Ethers

MOM ethers are the first and simplest of the acetal-type protecting groups whose prime virtues are ease of introduction. MOM ethers are the most robust of the alkoxymethyl ethers. In some cases, the conditions required to liberate a 

MOMa(82mmoO DIPEA (62 mmoq B114NI (0.92 mmoO 

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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-... 

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

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. 

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. 

Enantioselective reduction of prochiral acylstannanes (45) by (5)-BINAL-H [(S)-(28)] gives (/f)-a-hy-droxystannanes in reasonable chemical yields and consistently good optical yields (up to 96% ee). The unstable a-hydroxystannanes have been isolated and characterized after protection as methoxymethyl (MOM) ethers (46). In contrast, (S)-BINAL-H reduction of r-butylacylstannanes and a,p-unsaturated acylstannanes affords (5)-a-hydroxystannanes. ... 

After deprotection of the methoxymethyl (MOM) ether under acidic conditions, alcohol 319 was deoxygenated through the Barton procedure to obtain the natural alkaloid (—)-pyrinodemin A (Scheme 72) <20030L2611>. 

An efficient, versatile protocol for the synthesis of highly enantioenriched a-aminophosphonate has been devised. The addition of lithium diethyl phosphite in THF at room temperature to imines prepared from methyl and methoxymethyl (MOM) ethers of (7 )-(-)-2-phenylglycinol and a wide variety of aldehydes has been explored. The reaction generates predominantly the (R,R) diastereomers whose hydrogenolysis produces a-aminophosphonates in good yields (Scheme 8.67). 

With the basic skeleton of 47 and 48 in hand, we proceeded to incorporate the tethers (Scheme 13). The three-carbon tether was attached to the helicene unit by reacting the phenol of 53 with 3-bromo-l-propanol under basic conditions. Deprotection of the acetamide in 64 with KOH at reflux afforded the desired molecular rotary motor prototype 47 as a mixture of atropisomers. In an analogous way, the two-carbon tether was introduced by reaction of the phenol 53 with the methoxymethyl (MOM) ether of 2-bromoethanol. Deacetylation with KOH (—>66) and removal of the MOM group under acidic conditions led to the two-carbon tether molecular motor prototype 48, again as a mixture of three rotamers (Scheme 13). 

Another ether of 9 used as auxiliary is the methoxymethyl (MOM) ether 12 which forms amides with carboxylic acids for sigmatropic rearrangements (Section D. 1.6.3.2.) or enantiose-lective Birch reduction/alkylation (Section D. 1.1.1.3.1.). The ether is obtained by an analogous alkylation procedure with chloromethyl methyl ether15 6. 

All that remained in order to achieve spiroketalization was deprotection of the phenolic EOM groups. EOM ethers are known to be labile under similar reaction conditions to methoxymethyl (MOM) ethers, in particular Bronsted and Lewis acidic reagents. A survey of acidic deprotection conditions was therefore undertaken in order to elucidate optimal reaction conditions that would result in the formation of spiroketal 24 (Table 2). 

The protection of hydroxyl groups as methoxymethyl (MOM) ethers was achieved in a simple and convenient solvent-free reaction on alumina under sonication (Eq. 54).The reactions are generally reasonably fast and high-yielding and conditions are mild enough not to induce isomerization of double or triple bonds in allylic and propargylic alcohols. Alumina can be recycled after washing and reactivation. Without sonication, reactions were very slow. 

In the synthesis depicted in Fig. 10, White et al (52) converted the protected methoxymethyl (MOM) ether (30) derived from (29) into the aldehyde (31), followed by a Wittig reaction to obtain the E a,P-unsaturated ester (32). Subsequent reaction of the bis-MOM derivative (33) with lithium diisopropylamide furnished, via a fragmentation-recombination process, two diastereoisomers (34) and (35). After chromatographic separation of (34), its bis-ether derivative (36) was converted into... 

Ranu et al. employed Inl3 generated in situ to catalyze the conversion of THP and methoxymethyl (MOM) ethers to acetate, using the easily available but usually unreactive ethyl acetate [268, 269] (Figure 8.121). 

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