MTMS

Me2BBr, CUjClj, -78°, then NaHC03/H20, 87-95% yield. This reagent also cleaves the MEM, MTM, and acetal groups. Esters are stable to this reagent. 

Methylthiomethyl ethers are quite stable to acidic conditions. Most ethers and 1,3-dithianes are stable to the neutral mercuric chloride used to remove the MTM group. One problem with the MTM group is that it is sometimes difficult to introduce. 

HgCl2, CH3CN, H2O, 25°, 1-2 h, 88-95% yield. If 2-methoxyethanol is substituted for water, the MTM ether is converted to a MEM ether. Similarly, substitution with methanol affords a MOM ether. If the MTM ether has an adjacent hydroxyl, it is possible to form the formylidene acetal as a byproduct of cleavage. 

MezBBr, CH2CI2, -78° NaHC03, H2O, 87-95% yield. This method also cleaves MTM and MOM ethers and ketals. 

NCSBu2Sn)20 1%, THF, H20. Acetonides and TMS ethers are also cleaved under these conditions, but TBDMS, MTM, and MOM groups are stable. This catalyst has also been used to effect transesterifications. ... 

Some of the methods used to cleave methylthiomethyl (MTM) ethers should also be applicable to the cleavage of tetrahydrothiofuranyl ethers. 

Hg(C104)2, 2,4,6-collidine, acetone, H2O (9 1), 5 h NH3, dioxane, H2O (1 1). In this case Hg(II) is used to cleave the MTM group, liberating a hydroxyl group, which assists in the cleavage of the carbonate on treatment with ammonia. Cleavage by ammonia is 500 times faster for this hydroxy derivative than for the initial MTM derivative. 

HgCl2, CH3CN-H2O, reflux, 10 h, 90-95% yield. Aiyl methylthiomethyl ethers are stable to the conditions used to hydrolyze primary alkyl MTM ethers (e.g., HgCl2/CH3CN-H20, 25°, 6 h). They are moderately stable to acidic conditions (95% recovered from HOAC/THF-H2O, 25°, 4 h). 

Me2BBr, CH2CI2, — 78°, 90-97% yield.This reagent also cleaves MTM, MEM, and MOM ethers (87-95% yield). 

A 1,3-dithiane is stable to the conditions (HgCl2, CaC03, CH3CN-H2O, 25°, 1-2 h) used to cleave a methylthiomethyl (MTM) ether (i.e., a mono-thio acetal). ... 

Electrolysis Pt electrode, KOAc, AcOH, 10 V, 18-20° K2CO3, MeOH, 81-91% yield. These cleavage conditions could, in principle, be used to cleave the MTM group. 

Methylthiomethyl Ester (MTM Ester) RCOOCH2SCH3 (Chart 6) Formation... 

HCl, Et20, 6 h, 83-88% yield.Acidic deprotection of the BOC group could not be achieved with complete selectivity in the presence of an MTM ester. The trityl and NFS (2-nitrophenylsulfenyl) groups were the preferred nitrogen protective groups. 

Further elaboration of the MOM derivative E was carried out as described above for the MTM protected fragment B to afford fragment F which was converted to aplasmomycin by an 8-step sequence. 

MgBr2, ether, BuSH, rt, 40-97% yield. Tertiary and allylic MOM derivatives give low yields. MTM and SEM ethers are also cleaved, but MEM ethers axG stable." ... 

MTM ethers can be prepared from MEM and MOM ethers by treatment with Me2BBr to form the bromomethyl ether, which is trapped with MeSH and (t-Pr)2NEt. This method may have some advantage, since the direct preparation of MTM ethers is not always simple. ... 

AIH2CI, AIHCI2, or BH3 in toluene or THE. See the section on SEM ethers for a selectivity study of these reagents with the SEM, MTM, EOM (ethoxymethyl), andp-AOM groups."... 

BH3, toluene converts the p-AOM ether into a methyl ether. For a comparison of the stability of this group with MTM, SEM, BOM, and EOM to various hydride reagents, see the section on SEM ethers. ... 

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