Allyl ethers stable

NBS, CH3CN, H2O, 62-90% yield.The POM group has been selectively removed in the presence of an ethoxy ethyl ether, TBDMS ether, benzyl ether, p-methoxybenzyl ether, an acetate, and an allyl ether. Because the hydrolysis of a pentenyl 2-acetoxyglycoside was so much slower than a pentenyl 2-benzyloxyglycoside, the 2-benzyl derivative could be cleaved selectively in the presence of the 2-acetoxy derivative. The POM group is stable to 75% AcOH, but is cleaved by 5% HCl. 

Cp2Zr, then water, 66% yield.O-Allyl ethers are cleaved at a faster rate THP, acetonide. Bn ethers, and benzoates are stable. 

Alternative conditions for reductive decyanations can be used. The allylic ether in compound 26, an intermediate in a total synthesis of (-)-roxaticin, was prone to reduction when treated with lithium in liquid ammonia. Addition of the substrate to an excess of lithium di-ferf-butylbiphenylide in THF at -78°C, and protonation of the alkyllithium intermediate provided the reduced product 27 in 63% yield, as a single diastereomer (Eq. 7). a-Alkoxylithium intermediates generated in this manner are configurationally stable at low temperature, and can serve as versatile synthons for carbon-carbon bond forming processes (see Sect. 4). 

For allyl ethers 790 with R1 =Ph, treatment with LDA generates anions 791 which undergo [2,3]-Wittig rearrangement to more stable alkoxides 792 (Scheme 126). Spontaneous expulsion of benzotriazole anion from 792 generates (3,y-unsaturated ketones 793 that are isolated in high yields (86-92%) <1996JOC4035>. In the case of... 

Ru(H20)6], which is a precursor of ROM polymerization of cyclic dienes has also been found to possess good alkene isomerization activity [1], Among others it catalyzed the isomerization of allylphenyl ether to a vinylphenyl ether (Scheme 9.1) at room temperature. Allyl ethers are stable to acids and bases, while vinyl ethers are easily cleaved in acidic solutions. Therefore this isomerization gives a mild method for removal of protecting allyl groups under exceedingly mild conditions. 

Allyl ethers are also formed under PTC conditions (see Expt 5.73). These ethers are stable under moderately acidic and basic conditions. Deprotection is achieved by treatment with potassium t-butoxide in dimethyl sulphoxide, which results in rearrangement to the corresponding prop-l -enyl ether, followed by reaction with a mercury(n) chloride/mercury(n) oxide reagent mixture.78... 

PMB ethers can be cleaved oxidatively with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)11 in dichloromethane/water tor with cerium ammonium nitrate (CAN) in acetonitrile/water.12 Many other protecting groups such as esters, isopropylidene acetals, benzyl ethers, allyl ethers and f-butyldiphenyl silyl (TBDMS) ethers are stable to these conditions (Scheme 2.4). The cleavage reaction, with DDQ is initiated with a single-... 

For allyl ethers, rearrangement of the double bond to the more thermodynamically stable enol ether can be accomplished using trisjtriphenylphosphinejrho-dium(l) chloride (Wilkinson s catalyst). A possible mechanism for the rhodium(l)-... 

IVrtiary, bcnzylic, and allylic ethers cleave by an Sjjl or El mechanism hecauAO these substrates can produce stable interm iate carbocotions. These reactions arc often fast and take place at modcTate temperatures. /erf-Butylethers, for example, react by an El mechanism on treatment with trifluoroacetic acid at OX. 

A useM review on organomanganese reagents in organic synthesis has appeared. As described therein, one of the most stable alkyl Mn(II) reagents is trialkyl manganate, MnRs, which can be conveniently prepared as the Li+ or MgBr+ salt and used at 0 °C. These have been utilized for a variety of reactions, such as the stereoselective alkylation of gew-dibromocyclopropanes (Scheme 2), the silylation of acetylenes, and the radical cyclization of allylic ethers. Some of these transformations can be made catalytic. ... 

The allyloxycarbonyl group [269] has shown a wide application in organic synthesis, especially in the fields of peptides, nucleotides, and carbohydrates. Allyloxycarbonyl derivatives are more easily prepared than the corresponding allyl ethers and they are more stable than ester protecting groups which find frequent use in carbohydrate chemistry. 

Wilkinson s catalyst catalyzes the isomerization of an alkene to its thermodynamically most stable isomer. Isomerization of allyl ethers in this manner gives enol ethers, which can be hydrolyzed to give the free alcohol and a carbonyl compound. 

The allylic ether monomer I has also been copolymerized with 7V-aryl maleimides, but in this case the tin loading is quite low (0.5 mmol g ) and the polymer appears to be less stable, especially at higher temperature. ... 

Allyldiethylamine behaves similarly, but the yields are low since neither the starting amine nor the products are stable to the reaction conditions. For the efficiency of the cyclopropanation of the allylic systems under discussion, a comparison can be made between the triplet-sensitized photochemical reaction and the process carried out in the presence of copper or rhodium catalysts whereas with allyl halides and allyl ethers, the transition metal catalyzed reaction often produces higher yields (especially if tetraacetatodirhodium is used), the photochemical variant is the method of choice for allyl sulfides. The catalysts react with allyl sulfides (and with allyl selenides and allylamines, for that matter) exclusively via the ylide pathway (see Section 1.2.1.2.4.2.6.3.3. and Houben-Weyl, Vol. E19b, pll30). It should also be noted that the purely thermal decomposition of dimethyl diazomalonate in allyl sulfides produces no cyclopropane, but only the ylide-derived product in high yield.Very few cyclopropanes have been synthesized by photolysis of other diazocarbonyl compounds than a-diazo esters and a-diazo ketones, although this should not be impossible in several cases (e.g. a-diazo aldehydes, a-diazocarboxamides). Irradiation of a-diazo-a-(4-nitrophenyl)acetic acid in a mixture of 2-methylbut-2-ene and methanol gave mainly l-(4-nitrophenyl)-2,2,3-trimethylcyclo-propane-1-carboxylic acid (19, 71%) in addition to some O-H insertion product (10%). ... 

Sml2(5 eq./allyl group), THF, i-PrNH2 (20 eq.), H2O (15 eq.), 80-99% yield. Phenolic allyl ethers are cleaved at a faster rate. An anomeric allyl ether is completely stable and other substituted allyl ethers along with allyl amines and allyl sulfides are also not cleaved. ... 

SiCLt, Lil, BE3, CH3CN, toluene, 45 min to 15 h, 82-98% yield. BF3 was required to get good yields. Benzyl and allyl ethers are cleaved similarly, but methyl thioethers are stable. ... 

Pd(Ph3P)4, PMHS, ZnCl2, THF, rt, 89-92% yield. Allyl ethers and esters are cleaved similarly, but a prenyl ether is stable. 

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