Lithium allyl ethers

Lithium diphenyphosphide (THF, 25°, 2 h HCl, H2O, 87% yield) selectively cleaves an aryl methyl ether in the presence of an ethyl ether.It also cleaves a phenyl benzyl ether and a phenyl allyl ether to phenol in 88% and 78% yield, respectively. ... 

The rearrangement of an ether 1 when treated with a strong base, e.g. an organo-lithium compound RLi, to give an alcohol 3 via the intermediate a-metallated ether 2, is called the Wittig rearrangement. The product obtained is a secondary or tertiary alcohol. R R can be alkyl, aryl and vinyl. Especially suitable substrates are ethers where the intermediate carbanion can be stabilized by one of the substituents R R e.g. benzyl or allyl ethers. 

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). 

There are other means of generating the anions of allyl ethers. One of the most useful for synthetic purposes involves a lithium-tin exchange on stannylmethyl ethers (see Section 7.1.2.4).295... 

Hartwig et al. demonstrated that the same combination of iridium precursor and phosphoramidite LI also catalyzes allylic etherifications (Scheme 9) [68]. Lithium and sodium aryloxides were shown to react with cinnamyl and hex-2-enyl carbonates to form the branched allylic ethers in high yield, with high branched-to-linear... 

Wenn man Carbonsaure-nitrile bei — 78° mit Diisobutylalan in Pentan reduziert, das Pen-tan entfernt und den Riickstand bei — 78° mit Allyl- oder Benzyl-magnesiumchlorid bzw. mit Alkyl-lithium in Ether/Tetrahydrofuran umsetzt, erhalt man nach der hydrolytischen Aufarbeitung z. B. folgende Amine1. 

Metallated allylic ethers can also be used as partners in allylzincations of alkenyl-metals144. Allyl methyl ether could be metallated with s-BuLi in ether provided that TMEDA was present and, after transmetallation with ZnBr2, addition to the alkenyl-lithium derived from 205 proceeded slowly at room temperature. Nevertheless, after hydrolysis the corresponding allylic ether 227 was obtained with high diastereoselectivity (equation 110)146. 

Lithiated allyl sulfides (in common with allyl sulfoxides and selenides, but in contrast with allyl ethers and allyl amine derivatives) tend to react with alkyl halides at the a position, adjacent to S.1 The best a-selectivities are obtained with lithium-coordinating S-substituents such as pyridyl (114),85 imidazolyl (115), and dimethylaminocarbonyl (116).1... 

Lithium naphthalenide (prepared from lithium and 1.33 equivalents of naphthalene) also reductively cleaves benzyl ethers [Scheme 4.143],262 Some functionalities survive the reaction conditions like carbon-carbon double bonds, benzene rings, THP ethers, stlyl ethers and methoxymethyl ethers. A ketone group can be present but its prior conversion to an enolate is necessary. A similar transformation, but with a catalytic amount of naphthalene, has been reported.263 Although allyl ethers are also cleaved by the procedure, the selective deprotec-... 

Isomerisation of allyl ethers to enol ethers by Wilkinson s catalyst in refluxing aqueous ethanol is accompanied by competing reduction of the double bond to the propyl ether409-412 However, treatment of Wilkinson s catalyst with butyl-lithium results in a red rhodium catalyst that is able to isomerise a wide range of substituted and unsubstituted allylic ethers without competing reduction.413-414 In the example shown in Scheme 4.215, the unpurified enol ether product was cleaved by treatment with a mixture of mercury(Il) chloride and mercury(II) oxide in acetone to liberate the anomeric centre in 91% yield for the two steps.413-414... 

A number of investigations have explored the reactions of ally lie stannanes containing a y-alkoxy substituent. A direct preparation of these substances utilizes the kinetic deprotonation of an allyl ether followed by alkylation with tri-n-butylstannyl chloride. In a typical experiment, the deprotonation of 101 with 5-butyllithium leads to internal coordination of lithium cation and provides formation of the Z-allylstannane 102. The behavior of y-alkoxyallylstannanes is similar to the corresponding Z-alkylstannanes, and as a result, the reaction provides a stereoselective route for the synthesis of complex diol derivatives. In the allylation of chiral aldehyde 80 with stannane 102, /l-chelation dictates face selectivity. The expected. yyn, anti-product 104 is obtained with high diastereoselection via the antiperi-planar 103, which accommodates the sterically demanding silyl (TBS) ether (Scheme 5.2.23).23... 

One of die most popular reactions in organic chemistry is dissolving metal reductions [1-3], Two systems are frequently used - sodium dissolved in ammonia with alcohol and lithium dissolved in alkylamines [4]. Although calcium is seldom used, it has been successfully applied to the reduction of a variety of compounds and functional groups [5], including aromatic hydrocarbons, carbon-carbon double and triple bonds, benzyl ethers, allyl ethers, epoxides, esters, aliphatic nitriles, dithianes, als well as thiophenyl and sulfonyl groups. 

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