Benzyloxymethyl protecting group

From intermediate 12, the path to key intermediate 7 is straightforward. Reductive removal of the benzyloxymethyl protecting group in 12 with lithium metal in liquid ammonia provides diol 27 in an overall yield of 70% from 14. Simultaneous protection of the vicinal hydroxyl groups in 27 in the form of a cyclopentanone ketal is accompanied by cleavage of the tert-butyldimethylsilyl ether. Treatment of the resultant primary alcohol with /V-bromosuccini-mide (NBS) arid triphenylphopshine accomplishes the formation of bromide 7, the central fragment of monensin, in 71 % yield from 27. 

An N-benzyloxymethyl protecting group was removed on Pd black in EtOH at 45 psi H2 for 15 hours (Scheme 4.52).236... 

A new and direct synthesis of (Z)-trisubstituted allylic alcohols has appeared [equation (13)] involving a lithium-free Wittig reaction of unstabilized phosphor anes with acyclic a-alkoxyketones Z.E ratios are best for R = 2-tetrahydropyranyl but, where steric hindrance at the carbon atoms to be joined makes reaction sluggish, the less bulky benzyloxymethyl protecting group may be preferable. 

Tri.-nethylsilyl triflate (TMSOTf), PhSCH, CF3COOH. These conditions also cleave the following protective groups used in peptide synthesis (MeO)Z-, Bn-, Ts-, CI2C6H3CH2-, BOM (benzyloxymethyl)-, Mts-, MBS-, r-Bu-SR, Ad-SR, but not a BnSR, Acm, or Arg(N02) group. The rate of cleavage is reported to be faster than with TfOH/TFA. 

Both benzyl ether, benzyloxymethyl and t-butyldiphenylsilyl protecting groups were removed on Pd(OH)2/C in methanol-acetone (Scheme 4.35).165... 

A -Benzyl groups on pyrimidinones and quinazolinones are removable by hydrogenolysis, although it is now more common to use a PMB substituent that can be removed with either TFA or CAN. Other N-protecting groups to be commonly used include benzyloxymethyl (BOM), removable by hydrogenation, ferZ-butoxycarbonyl (BOC), removable by anhydrous acid, and pivaloyloxymethyl (POM), which is removable by methanolic ammonia at room temperature. Alkenyl pyrimidinones have been employed in 1,3-dipolar cycloaddition reactions to prepare heterocyclic nucleotides. 

Benzyl and benzyloxymethyl (CH2OCH2C6H5) are useful protective groups for the reduction, since both are removed by use of BBr3.2... 

Several compounds have been synthesized starting from 2-benzyloxymethyl-4,5-dichloro-3(2//)-pyridazinone (133) (Scheme 24) <93H(36)519>. First, it was allowed to react with A-benzylamino-ethanol in water or toluene. The ring closure of the precursors (134) and (136) to oxazinones (135) and (137) was achieved with sodium ethoxide in ethanol. The protection groups could be selectively removed as described in Section 7.19.3.1.2 <8iMl 7i9-oi>. 

Ten years later, a Japanese group led by Oikawa developed a mechanistically related method for the selective debenzylation of substituted benzyl ethers based on the reagent 2,3-dichloro-S,6-dicyanobenzo-quinone (DDQ). In contrast to the trityl tetrafluoroborate reaction, the oxidation proceeds at room temperature in the presence of water. Furthermore, under these convenient and essentially neutral conditions, many functional groups, including other common protecting groups, such as isopropylidine, methoxy-methyl, benzyloxymethyl, tetrahydropyranyl, acetyl, r-butyldimethylsilyl, benzyl, benzoyl and tosyl, are unaffected. As a result of the hig levels of selectivity which can be achieved, this method for the depro-... 

Acyclic 0,0-acetals are used for the temporary protection of mono-alcohols. Most commonly used are the tetrahydropyranyl (THP), the methoxymethyl (MOM), the benzyloxymethyl (BOM), or the methoxyethoxymethyl (MEM) protecting groups. 

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. 

The addition, alteration, or removal of protecting groups will not be discussed here Ac = Acetyl, Ar = 2,4,6-triisopropylphenyl. Bn = benzyl, Bz = benzoyl, BOC = rerf-butoxycar-bonyl, BOM = benzyloxymethyl, TBPS = tert-butyldiphenylsilyl, TBS = fert-butyldime-thylsilyl, TES = triethylsilyl, TIPS = triisopro-pylsilyl, TMS = trimethylsilyl. Actual yields of the first published procedures are given, conversions and loss to formation of isomers were included in the calculations where necessary. For precursors the yields were taken from the references given by the authors and used to... 

A convenient synthesis of (— )- xo-brevicomin (87) utilizes a radical chain reaction of methyl vinyl ketone with (45, 5R)-4-benzyloxymethyl-5-iodomethyl-2,2-dimethyl-l,3-dioxo-lane (209), prepared by treating the (R,R)-tartaric acid derivative 141 with triphenylpho-sphonium iodide in the presence of imidazole. Adduct 215, after acidic hydrolysis of the isopropylidene protecting group, furnishes the bicyclic acetal 216. Subsequent debenzylation and tosylation followed by methylation with lithium dimethylcuprate provides 87 in an overall yield of 17% from (R,R)-tartaric acid. The optical purity of 87 corresponds to greater than 99% ee (Scheme 50). Carrying out a similar series of transformations with ( S,5)-tartaric acid leads to ( + )-exo-brevicomin (90) [78]. 

Imidazole protection, temporary protection of the basic and nucleophilic imidazole group of histidine during peptide synthesis. The imidazole moiety has two nonequivalent, but similarly reactive nitrogen atoms, designated tt and r, which cause difficulties in both protection and His racem-ization in peptide synthesis. By application of Boc/Bzl tactics, the jr-benzyloxymethyl (Bom) group is suitable as it prevents racemization and can be cleaved by HE. For Fmoc/Bu chemistry, the best acid-labUe blocking group seems to be r-trityl, as it is stable to bases and cleavable by aqueous TEA at room temperature [T. Brown et al., J. Chem. Soc., Perkin Trans 11982, 1553 P. Sieber, B. Riniker, Tetrahedron Lett. 1987, 28, 6031]. 

Moreover, a VNS was a key step in the first synthesis of pyrrolo[3,2-e]indole -a heterocyclic fragment of the antitumor antibiotic CC 1065. The a-cyano side chain is installed at the C-4 position on V-(benzyloxymethyl)-5-nitroindole 39 in good yield [25]. This intermediate (40) is then reductively cyclized using Pd(C) to produce the new ring system 41 in 69% yield however, the protecting group does not remain intact at 65°C. If this reaction is carried out at 45°C, the benzyloxy-methyl (BOM) group is left intact, and the pyrrolo[3,2-c]indole is isolated in 62%. 

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