Allylation: of alcohols

This method can be extended for the synthesis of allyl alkyl ethers from alcohols with allyl acetate. Thus, the iridium cationic complex [lr(cod)2] BFc, catalyzes the allylation of alcohols 71 with allyl acetate 72 to afford allyl ethers 73 (Equation 10.14) [30]. 

The allylation of alcohols was applied to the intramolecular cyclization of hydroxyallylsilanes which were converted into 5- and 6-membered -methylene cyclic ethers [17] ... 

Stereoselective formation of 3-methylenetetrahydrofuran such as 180 by intramolecular allylation of alcohol with allyl benzoate in 179 was utilized in synthetic studies of the core of amphidinolide [70]. Thus treatment of 179 with Pd(OAc)2 and PPh3 in the presence of Me3SnCl (1 equiv.) and NaH in THF afforded the cA-tetrahydrofuran 180 stereoselectively in 77 % yield. In this reaction, the less reactive hydroxy group was converted to the more reactive tin alkoxide by the reaction of Me3SnCl (1 equiv.) and NaH. 

In contrast to less efficient allylation of alcohols, allylation of phenols proceeds much more smoothly. In the enantioselective synthesis of (—)-galanthamine by Trost, two Pd-catalyzed reactions were utilized. Asymmetric allylation of the bro-movanillin 191 with the cyclic allylic carbonate 192 gave the ether 193 by using ( ] -allyl-PdCl)2 and chiral Trost L-2. Subsequent Heck reaction of 194 afforded 195 in 91 % yield when DPPP was used as a ligand. DPPF and DPPE gave lower yield [74]. 

A very simple method for the allylation of alcohols with allylsilane was reported. Different Lewis acids (AICI3, Sc(OTf)3, Bi(OTf)3...) had been examined for this reaction but catalytically these were inefficient. Bismuth(III) chloride was proved to be the best catalyst. The reaction of benzhydrol or its derivatives with silyl nucleophile in the presence of 1 mol% at room temperature afforded the desired alkenes in good yields without any side product. A higher temperature was needed to allylate other alcohols such as phenylethanol. Aliphatic alcohols were not suitable for this system (Equation 3) [25d]. 

Simple esters cannot be allylated with allyl acetates, but the Schiff base 109 derived from o -amino acid esters such as glycine or alanine is allylated with allyl acetate. In this way. the o-allyl-a-amino acid 110 can be prepared after hydrolysis[34]. The Q-allyl-o-aminophosphonate 112 is prepared by allylation of the Schiff base 111 of diethyl aminomethylphosphonates. [35,36]. Asymmetric synthesis in this reaction using the (+ )-A, jV-dicyclohex-ylsulfamoylisobornyl alcohol ester of glycine and DIOP as a chiral ligand achieved 99% ec[72]. 

Allylamines are difficult to cleave with Pd catalysts. Therefore, amines are protected as carbamates, but not as allylamines. Also, allyl ethers used for the protection of alcohols cannot be cleaved smoothly, hence alcohols are protected as carbonates. In other words, amines and alcohols are protected by an allyloxycarbonyl (AOC or Alloc) group. 

The use of allyl ethers for the protection of alcohols is common in carbohydrate literature because allyl ethers are generally compatible with the various methods... 

The section on the cleavage of allyl ethers of alcohols should also be consulted. 

Dimethyl sulfoxide reacts with trifluoroacetic anhydride at low tempera ture to give a complex that is an efficient reagent for the oxidation of alcohols to carbonyl compounds [40 41] This reagent can be used to oxidize primary and secondary aliphatic alcohols, cycloalkyl alcohols, and allylic, homoallylic, ben-zylic, acetylenic, and steroidal alcohols (equation 19)... 

Butyl ethers can be prepared from a variety of alcohols, including allylic alcohols. The ethers are stable to most reagents except strong acids. The /-butyl ether is probably one of the more underused alcohol protective groups, considering its stability, ease and efficiency of introduction, and ease of cleavage. 

Stoichiometric organocoppcr reactions become more y selective in the presence of boron trifluoride or trialkylboranes1Thus, RCu BF3 gives y substitution with allylic halides, alcohols, carboxylates and mesylates1119. 

More recently, Brown and Fallis138 have described a similar epimerization of bicyclic and allylic tertiary alcohols, such as, for example, the epimerization of the endo alcohol 78 to its exo epimer 79 (equation 36). An exo-to-endo ratio of 8 to 1 was obtained in this case. 

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