PMB reagent

AD-mix-P 9-BBN Bn Boc Bz BOM CDI m-CPBA CSA Cy DBU DDQ DEAD DIAD DIBAL-H DIPT DME DMF DMAP DMSO EDC HMPA HOBT KHMDS LDA MEM MOM MoOPH NaHMDS NBS NMM NMO Piv PMB Reagent for Sharpless asymmetric dihydroxylation 9-Borabicyclo[3.3.1 ]nonyl Benzyl t-Butoxy carbonyl Benzoyl B enzyloxy methyl Carbonyldiimidazole m-Chloroperoxybenzoic acid Camphorsulfonic acid Cyclohexyl 1,8 -Diazabicy clo[5.4.0] undec-7-ene 2,3 -Dichloro-5,6-dicyano-p-benzoquinone Diethyl azodicarboxylate Diisopropyl azodicarboxylate Diisobutylaluminum hydride Diisopropyl tartrate Dimethoxyethane A,N-Dimethylformamide 4-Dimethylaminopyridine Dimethyl sulfoxide N-(3-Dimethylaminopropyl)-A -ethylcarbodiimide Hexamethylphosphoramide 1 -Hydroxybenzotriazole Potassium hexamethyldisilazane Lithium diisopropylamide Methoxyethoxymethyl Methoxymethyl Oxidodiperoxymolybdenum(pyridine)(hexamethylphophoramide) Sodium hexamethyldisilazane N - Bromosuccinimide A-Methylmorpholine A-Methylmorpholine A-oxide Pivaloyl /j-Methoxybenzyl... 

The Dudley PMB reagent can also be activated under mildly acidic conditions using catalytic camphorsulfonic acid (CSA) in lieu of CHsOTf (Example 3). ... 

The Dudley reagents are employed for the protection of alcohols as benzyl or PMB ethers, respectively, under mild conditions. Carboxylic acids are readily protected as well. Activation of the appropriate Dudley reagent in the presence of an alcohol furnishes the desired aiylmethyl ether. The benzyl reagent is activated upon warming to approximately 80-85 °C, whereas activation of the PMB reagent occurs at room temperature upon treatment with methyl triflate (CHsOTf) or protic acid." Aromatic solvents, most commonly trifluorotoluene, often provide the best results. Magnesium oxide (MgO) is typically included in the reaction mixture as an acid scavenger. For benzylation of carboxylic acids, triethylamine (EtsN) is used in place of MgO. ... 

Six protective groups for alcohols, which may be removed successively and selectively, have been listed by E.J. Corey (1972B). A hypothetical hexahydroxy compound with hydroxy groups 1 to 6 protected as (1) acetate, (2) 2,2,2-trichloroethyl carbonate, (3) benzyl ether, (4) dimethyl-t-butylsilyl ether, (5) 2-tetrahydropyranyl ether, and (6) methyl ether may be unmasked in that order by the reagents (1) KjCO, or NH, in CHjOH, (2) Zn in CHjOH or AcOH, (3) over Pd, (4) F", (5) wet acetic acid, and (6) BBrj. The groups may also be exposed to the same reagents in the order A 5, 2, 1, 3, 6. The (4-methoxyphenyl)methyl group (=MPM = p-methoxybenzyl, PMB) can be oxidized to a benzaldehyde derivative and thereby be removed at room temperature under neutral conditions (Y- Oikawa, 1982 R. Johansson, 1984 T. Fukuyama, 1985). 

The PMBs, when treated with electrophilic reagents, show much higher reaction rates than the five lower molecular weight homologues (benzene, toluene, (9-, m- and -xylene), because the benzene nucleus is highly activated by the attached methyl groups (Table 2). The PMBs have reaction rates for electrophilic substitution ranging from 7.6 times faster (sulfonylation of durene) to ca 607,000 times faster (nuclear chlorination of durene) than benzene. With rare exception, the PMBs react faster than toluene and the three isomeric dimethylbenzenes (xylenes). 

Aldehyde 11 is first crolylaled with the ent-1 enantiomer of the reagent discussed above, leading to compound 34. Mild oxidation of the PMB protecting group with DDQ results in the p-methoxyphe-n>] protecting group, which corresponds to an acetal of anisalde-hyde.15, If>... 

Application of the previously described reaction sequence allows an initial insertion reaction with dichloromethyllithium to give 20 Then 20 is enhanced by one C, residue using Grignard reagent 21 to produce 22. Another reaction with dichloromethyllithium results in a C chain extension to product 5. Since the insertion reaction with dichloromethyllithium was conducted twice, the distance between the boron atom and the PMB ether inemases by two carbon atoms. 

Among the other reagents listed, activated Mn02 is specific for the oxidation of allylic and ben/ylie alcohols.22 KM11O4 is used for the oxidation of alkenes to diols.23 Ceriv(lV) ammonium nitrate (CAN) accomplishes oxidative cleavage of the PMB protecting group. 

As Fetizon s oxidation is carried out under neutral conditions, acid-and base-sensitive protecting groups resist its action. The oxidation-sensitive p-methoxybenzyl (PMB) protecting group resists the action of Fetizon s reagent.12... 

Figure 1. Modifications of sulfhydryl groups (a) DTNB or Ellman s reagent (b) 4,4 -dithiodipyridine (c) NEM (d) PMB (e) hydrogen peroxide oxidations.

The left part of the target molecule has now been made After deprotection of the PMB-protected alcohol with DDQ (72), the primary alcohol is oxidized to the aldehyde with the IBX reagent. Then, a Wittig reaction with PhsP CHCHs formed in situ transforms the carbonyl compound into a Z-configured alkene. At this stage, separation of the C-5-isomers is possible to obtain diastereopure 30. 

DDQ is a standard reagent for /7 /ra-methoxybenzyl (PMB) deprotection. The resulting free hydroxyl group is then oxidized to the corresponding aldehyde, which undergoes a subsequent Takai olefination. 

Triethylsilyl ethers have been used as protective groups in Grignard additions, Swern and Dess-Martin oxidations, Wittig reactions, metallations with R2NLi reagents, and cleavage of RO-PMB ethers with DDQ. 

An allylic MPM ether has been converted directly to a bromide upon treatment with Me2BBr (5 min, -78"C). The reagent CBr4/TPP (CH2CI2, 0-30°C) is more general and converts alkyl, allyl, and benzyl PMB derivatives to bromides in 45-94% yield. ... 

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