Rearrangement of epoxides to allylic alcohols

BASE-INDUCED REARRANGEMENT OF EPOXIDES TO ALLYLIC ALCOHOLS trans-Pinocarveol,... 

TT-ALLYLNICKEL HALIDES METHALLYLBENZENE, 52, 115 Rearrangement of epoxides to allylic alcohols, 53, 17 Reduction, by controlled-po-tential electrolysis, 52, 22 by lithium aluminum hydride of exo-3,4-dichlorobicyclo [3.2.l]oct-2-ene to 3-chlorobicyclo[3.2.l]oct-2-ene, 51, 61... 

Enantioselective deprotonation.2 The rearrangement of epoxides to allylic alcohols by lithium dialkylamides involves removal of the proton syn to the oxygen.3 When a chiral lithium amide is used with cyclohexene oxide, the optical yield of the resulting allylic alcohol is 3-31%, the highest yield being obtained with 1. 

Enantioselective rearrangement of epoxides to allylic alcohols 91TA1. Photochemical reactions of glycidyl esters 92MI11. 

II. CHIRAL LITHIUM AMIDES IN ASYMMETRIC SYNTHESIS A. Rearrangement of Epoxides to Allylic Alcohols... 

The (3-elimination of epoxides to allylic alcohols on treatment with strong base is a well studied reaction [la]. Metalated epoxides can also rearrange to allylic alcohols via (3-C-H insertion, but this is not a synthetically useful process since it is usually accompanied by competing a-C-H insertion, resulting in ketone enolates. In contrast, aziridine 277 gave allylic amine 279 on treatment with s-BuLi/(-)-spar-teine (Scheme 5.71) [97]. By analogy with what is known about reactions of epoxides with organolithiums, this presumably proceeds via the a-metalated aziridine 278 [101]. 

The well-known base-mediated rearrangement of epoxides into allylic alcohols was first reported as an enantioselective process using a chiral base in 1980. Since then, the reaction has received much attention, mostly due to the significance of chiral allylic alcohols in organic synthesis. Major breakthroughs in the area include the use of a substoichiometric amount of chiral base and the development of chiral bases for a true catalytic reaction protocol. Andersson and co-workers have reviewed this area from 1980 to 2001, with emphasis on the period 1997-2001 <2002CSR223>. 

Titanium-IV compounds with their Lewis acid activity may catalyze an interfering rearrangement of the starting allylic alcohol or the epoxy alcohol formed. In order to avoid such side-reactions, the epoxidation is usually carried out at room temperature or below. 

Isomerization of primary allylic alcohols proceeds in dichloromethane at 25 °C in the presence of a catalyst prepared in situ from VO(acac)2 or Mo02(acac)2 and BTSP to give tertiary isomers in good yields. This is in sharp contrast to the well-known Sharpless epoxidation of allylic alcohols. The catalysts are also effective for rearrangements of secondary-tertiary allylic alcohols. The isomerization of an allenyl allylic... 

Rearrangement of 1,2-disubstituted compounds Diethoxytriphenylphosphorane, 109 epoxides to allylic alcohols Methylmagnesium N-cyclohexylisopro-pylamide, 189... 

Isomerization of epoxides to allylic alcoholsThis rearrangement has been effected with strong bases and various Lewis acids. Enantioselective rearrangement to optically active allylic alcohols can be effected with catalytic amounts of vitamin B, at 25°. Thus cyclopentene oxide rearranges to (R)-2-cyclopentene-l-ol in 65% ee. The rearrangement of the as-2-butene oxide to (R)-3-butene-2-ol in 26% ee is more typical. 

While several stoichiometric chiral lithium amide bases effect the rearrangement of raeso-epoxides to allylic alcohols [1], few examples using catalytic amounts of base have been reported. Asami applied a pro line-derived ligand to the enantioselective deprotonation of cyclohexene oxide to afford 2-cyclohexen-... 

Propylene oxide-based glycerol can be produced by rearrangement of propylene oxide [75-56-9] (qv) to allyl alcohol over triUthium phosphate catalyst at 200—250°C (yield 80—85%) (4), followed by any of the appropriate steps shown in Figure 1. The specific route commercially employed is peracetic acid epoxidation of allyl alcohol to glycidol followed by hydrolysis to glycerol (5). The newest international synthesis plants employ this basic scheme. 

Lithium amide deprotonation of epoxides is a convenient method for the preparation of allylic alcohols. Since the first deprotonation of an epoxide by a lithium amide performed by Cope and coworkers in 19585, this area has received much attention. The first asymmetric deprotonation was demonstrated by Whitesell and Felman in 19806. They enantioselectively rearranged me.vo-cpoxidcs to allylic alcohols for example, cyclohexene oxide 1 was reacted with chiral bases, e.g. (S,S) 3, in refluxing TFIF to yield optically active (/ )-2-cyclohexenol ((/ )-2) in 36% ee (Scheme 1). 

The application of the chiral base 10b has been extended to the rearrangement of epoxides cis- and trans-5 to give allylic alcohols in 97% and 68% ee, respectively (Scheme 7). 

In the first approach shown in Scheme 9, ketoester 77 was alkylated successively with 4-bromobutene and 1,3-dibromopropene. After decarboxylation, 78 was converted into iV-aziridinylimine 79 in good yield. The pivotal radical cyclization reaction proceeded smoothly to produce a mixture of isomeric propellane compounds 80, which was purified after the epoxidation step. For the synthesis of modhephene, the mixture of epoxides was rearranged into the corresponding allylic alcohols 81 and then the allylic alcohols were oxidized, giving a separable mixture of unsaturated ketones 82a and 82b. The major product 82a possessed the correct stereochemistry of the methyl group of modhephene. Since 82a had already been converted into modhephene, a formal total synthesis of dZ-modhephene has thus been completed. The isomeric ratio of 80 reflects the stereoselectivity during the radical cyclization reaction. The selectivity was very close to the ratio reported by Sha in his radical cyclization reaction. ... 

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