Substituted epoxides by lithiation of terminal epoxides

Diamine-ligand-assisted direct hydrogen-lithium exchange allows the generation of nonstabilized (H-substituted) oxiranyllithium species and their subsequent trapping by Bu(3)SnCl and carbonyl-based electrophiles. This reaction provides a new concise route to alpha,beta-epoxystannanes and substituted epoxides.     

Enantioselective synthesis of epoxides by alpha-deprotonation--electrophile trapping of achiral epoxides

Enantioselective alpha-deprotonation of achiral epoxides 1, 21, and 26 using organolithiums in the presence of (-)-sparteine 2 and subsequent electrophile trapping gives access to enantioenriched trisubstituted epoxides 9-17, 22, 23, 27 and 28 (in up to 86% ee).     

Intramolecular cyclopropanation of unsaturated terminal epoxides

Efficient lithium amide-induced intramolecular cyclopropanation of bishomoallylic and trishomoallylic epoxides is described. The methodology is used in an asymmetric synthesis of sabina ketone.     

Highly enantioselective ylide-mediated synthesis of terminal epoxides

The highly efficient asymmetric epoxidation of aldehydes by methylene transfer is now possible using new sulfonium salts.     

Fluorous biphasic hydrolytic kinetic resolution of terminal epoxides

Although application of light-fluorous techniques facilitates the isolation of reaction products from the hydrolytic kinetic resolution (HKR) of terminal epoxides catalysed by cobalt complexes of salen ligands, the extension of the original fluorous biphasic approach to this reaction is far from being a trivial exercise. The nature of the counter anion has a dramatic effect on the catalytic activity of heavily fluorinated chiral (salen) cobalt(III) complexes. Excellent enantioselectivities are obtained in the fluorous biphasic HKR of 1,2-hexene oxide when fluorinated anions are introduced (e.e.s up to 99% both for the diol and the epoxide), with C₈F₁₇COO^- affording reaction rates even higher than those observed with non-fluorous systems.     

锌和锡参与下末端环氧化物的选择性烯丙基化反应

烯丙基溴和金属辛或锡成功地将末端环氧化合物1一锅法合成高烯丙基醇2和双高烯丙基醇3. 还研究了环氧化合物取代基的影响, 并提出了此烯丙基化的反应途径 .     

Intramolecular cyclopropanation of unsaturated terminal epoxides and chlorohydrins

Lithium 2,2,6,6-tetramethylpiperidide (LTMP)-induced intramolecular cyclopropanation of unsaturated terminal epoxides provides an efficient and completely stereoselective entry to bicyclo[3.1.0]hexan-2-ols and bicyclo[4.1.0]heptan-2-ols. Further elaboration of C-5 and C-6 stannyl-substituted bicyclo[3.1.0]hexan-2-ols via Sn-Li exchange/electrophile trapping or Stille coupling generates a range of substituted bicyclic cyclopropanes. An alternative straightforward cyclopropanation protocol using a catalytic amount of 2,2,6,6-tetramethylpiperidine (TMP) allows for a convenient (1 g-7.5 kg) synthesis of bicyclo[3.1.0]hexan-2-ol and other bicyclic adducts. The synthetic utility of this chemistry has been demonstrated in a concise asymmetric synthesis of (+)-beta-cuparenone. The related unsaturated chlorohydrins also undergo intramolecular cyclopropanation via in situ epoxide formation.     

Enamines from terminal epoxides and hindered lithium amides

A new reactivity mode of lithium amides with epoxides leads to hindered enamines. The reaction of some of these enamines with unactivated primary and secondary alkyl halides is described, which expands the range of electrophiles that one can use in the synthesis of mono-alkylated aldehydes.     

Carbonylative ring opening of terminal epoxides at atmospheric pressure

The carbonylative opening of terminal epoxides under mild conditions has been developed using Co2(CO)8 as the catalyst. Under 1 atm of carbon monoxide and at room temperature in methanol, propylene oxide is converted to methyl 3-hydroxybutanoate in up to 89% yield. This transformation is general for many terminal epoxides bearing alkyl, alkenyl, aryl, alkoxy, chloromethyl, phthalimido, and acetal functional groups. The opening takes place without epimerization at the secondary stereocenter.     

Substituted aziridines by lithiation-electrophile trapping of terminal aziridines

[reaction: see text] Regio- and stereoselective deprotonation of N-Bus (Bus = tert-butylsulfonyl)-protected terminal aziridines with lithium 2,2,6,6-tetramethylpiperidide generates a nonstabilized (H-substituted) aziridinyl anion that undergoes in situ or external electrophile trapping under experimentally straightforward conditions to give trans-disubstituted aziridines in good to excellent yields.     

A novel one-step oxidation of terminal epoxides to allylic aldehydes

Various gibberellin epoxides have been oxidised with sulphuryl chloride to α,β-unsaturated aldehydes in < 70% isolated yield. This novel one-step oxidation occurs in the presence of hydroxy (except at C-13), ester, lactone and olefinic functions.     

A direct method for the conversion of terminal epoxides into gamma-butanolides

A new and efficient process for the conversion of terminal epoxides to gamma-butanolides is described involving Lewis acid promoted epoxide ring-opening by 1-morpholino-2-trimethylsilyl acetylene. Addition of a terminal epoxide to a solution of the ynamine and boron trifluoride diethyl etherate in dichloromethane at 0 degrees C rapidly affords a cyclic keteneaminal that can be hydrolyzed and protodesilylated under mild conditions to provide the corresponding gamma-butanolide in high yield. The net transformation is equivalent to an acetate enolate opening of terminal epoxides. The formation of a cyclic keteneaminal as the direct addition product was observed by monitoring of the reaction by IR and NMR spectroscopy. Functionalized gamma-lactones were prepared by the interception of the reactive cyclic keteneaminal prior to hydrolysis. Reactions with enantiomerically enriched terminal epoxides provide the corresponding gamma-butanolides without loss of optical activity. The compatibility of the present methodology with a wide range of functional groups is noteworthy.     

Intramolecular trapping by epoxides of intermediates generatedby organocuprate additions to propiolate esters.

The facility with which intramolecular trapping of the intermediates generated by conjugate addition of organocopper nucleophiles to propiolate esters may be effected by internal epoxides is critically dependent on the nature of the nucleophile.     

Direct catalytic synthesis of enantiopure 5-substituted oxazolidinones from racemic terminal epoxides

A venerable scaffold for asymmetric synthesis and drug development, chiral 5-substituted oxazolidinones are obtained in almost enantiomerically pure form (up to 99.9% ee) starting from racemic terminal epoxides. The salient features of this process include the very simple and convenient experimental protocol and the employment of a readily accessible catalyst and inexpensive, easily handled starting materials. An enantioconvergent approach for the total conversion of racemic epoxide into a single stereoisomeric oxazolidinone is also described.     

Highly selective hydrolytic kinetic resolution of terminal epoxides catalyzed by chiral (salen)Co(III) complexes. Practical synthesis of enantioenriched terminal epoxides and 1,2-diols

The hydrolytic kinetic resolution (HKR) of terminal epoxides catalyzed by chiral (salen)Co(III) complex 1 x OAc affords both recovered unreacted epoxide and 1,2-diol product in highly enantioenriched form. As such, the HKR provides general access to useful, highly enantioenriched chiral building blocks that are otherwise difficult to access, from inexpensive racemic materials. The reaction has several appealing features from a practical standpoint, including the use of H(2)O as a reactant and low loadings (0.2-2.0 mol %) of a recyclable, commercially available catalyst. In addition, the HKR displays extraordinary scope, as a wide assortment of sterically and electronically varied epoxides can be resolved to > or = 99% ee. The corresponding 1,2-diols were produced in good-to-high enantiomeric excess using 0.45 equiv of H(2)O. Useful and general protocols are provided for the isolation of highly enantioenriched epoxides and diols, as well as for catalyst recovery and recycling. Selectivity factors (k(rel)) were determined for the HKR reactions by measuring the product ee at ca. 20% conversion. In nearly all cases, k(rel) values for the HKR exceed 50, and in several cases are well in excess of 200.     

2-Ene-1,4-diols by dimerization of terminal epoxides using hindered lithium amides

[reaction: see text] Reaction of hindered lithium amides with readily available (enantiopure) terminal epoxides gives 2-ene-1,4-diols via carbenoid dimerization of the corresponding alpha-lithiated epoxides. D-Mannitol and D-iditol were synthesized using this method in three steps from (S)-tritylglycidyl ether.     

Enantioselective synthesis of 2,2-disubstituted terminal epoxides via catalytic asymmetric Corey-Chaykovsky epoxidation of ketones

Catalytic asymmetric Corey-Chaykovsky epoxidation of various ketones with dimethyloxosulfonium methylide using a heterobimetallic La-Li(3)-BINOL complex (LLB) is described. The reaction proceeded smoothly at room temperature in the presence of achiral phosphine oxide additives, and 2,2-disubstituted terminal epoxides were obtained in high enantioselectivity (97%-91% ee) and yield ( > 99%-88%) from a broad range of methyl ketones with 1-5 mol% catalyst loading. Enantioselectivity was strongly dependent on the steric hindrance, and other ketones, such as ethyl ketones and propyl ketones resulted in slightly lower enantioselectivity (88%-67% ee).     

Interaction of terminal epoxides of α-geranyl and α-farnesyl acetates with fluorosulfonic acid

The interaction of 7,8-epoxygeranyl acetate and of 11,12-epoxy-E,E-farnesyl acetate with fluorosulfonic acid forms products of the opening of the epoxide ring.