Epoxide To allylic alcohol

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]. 

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... 

Because of the mildness of the procedure, this is probably the best means of accomplishing this conversion. The selenoxide reaction has been used in a procedure for the conversion of epoxides to allylic alcohols.229... 

Isomerization of u,fi-unsaturated epoxides. This base is superior to LDA or lithium diethylamide for isomerization of a,/ -unsaturatcd epoxides to allylic alcohols with a trans double bond.1--Examples ... 

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. 

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

Enantioselective Isomerization of meso-Epoxides to Allylic Alcohols... 

The catalytic isomerization of meso-epoxides to allylic alcohols has been achieved with chiral cobalt complexes, in particular with cobalamin (vitamin B12) [47, 48]. 

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... 

Acetals as Chiral Auxiliaries. There have been many applications of acetals of 2,4-pentanediol as chiral auxiliaries to control the diastereoselectivity of reactions on another functional group. Examples include cyclopropanation of alkenyl dioxanes, lithium amide-mediated isomerization of epoxides to allylic alcohols, and addition of dioxane-substituted Grignard reagents or organolithiums to aldehydes. 

Nozaki and Yamamoto reported a novel method for regiospecific isomerization of epoxides to allylic alcohols based on diethylaluminum 2,2,6,6-tetramethylpiperidide (DATMP) which can be prepared in situ from Et2AlCl and lithium 2,2,6,6-tetramethylpiperidide (LiTMP) (molar ratio 1 1) in benzene at 0 °C for 30 min [119], Reaction of DATMP (4 equiv.) with ( )-cyclododecene oxide in benzene at 0 °C for 3 h produced ( )-2-cyclododecen-l-ol in 90 % yield. Interestingly, the reaction of diepoxide 121, a useful synthetic intermediate in the preparation of Cig-Cecropia juvenile hormone, with DATMP furnished the triol 122 in 41 % yield (Sch. 83). 

In addition to the formation of silyl enol ethers, isomerization of epoxides to allylic alcohols is another highly typical transformation performed by combination of a silicon Lewis acid with a tertiary amine. Reaction with la was examined, and its scope and limitation reported, by Noyori [61]. Epoxide 44 can be successfully converted into the corresponding allyl silyl ether 45 (Sch. 34). 

The conversion of epoxides to allylic alcohols (Scheme 24) can also be considered here. A variety of reagents, including lithium diethylamide, r-butyldimethylsilyl iodide, a dialkylboryl triflate and an ethylaluminum dialkylamide have been used successfully. 

AUylic alcohols and amines. Isomerization of epoxides to allylic alcohols by Te-NaBH probably involves epitelluride intermediates. Formation of allylic amines from aziridines requires the presence of a sulfonyloxy group at the a-position. 

The transformation of epoxides to allylic alcohols by the use of lithium dialkylamides is well known Consequently, it should be possible to apply this reaction to the asymmetric synthesis of allylic alcohols by the selective deprotonation of the enantiotopically related protons in symmetrical epoxides. 

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-... 

Epoxide isomerization. This strong base combination converts epoxides to allylic alcohols. The regiochemistry of the ring opening can be directed by a proximal heteroatom in the substrate. 

Isomerization of epoxides to allylic alcohols. This reaction is usually carried out with base (lithium diethylamide, 1, 610-611 2, 247-248 4, 298). Japanese chemists have used instead this new reagent of the type R R NAl(C2Hs)2, which is effective because of the affinity of aluminum for oxygen. Of several species, DATMP proved most satisfactory. It effects the isomerization of (1) and of (3) in high yield under very mild conditions. Note, however, that the oxides of cyclopentene, cyclohexene, and cycloheptene are stable under the same conditions. 

A rise in the content of hydroxyl groups and double bonds was, however, observed during copolymerization without HA compounds by Tanaka and Kakiuchi . These groups and unsaturation can arise by base — or acid-catalyzed isomerization of epoxides to allyl alcohol derivatives (and references cited therein). In the... 

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