Aminolysis of glycal-derived allyl epoxides and activated aziridines. Effects of the absence of coordination processes on the regio- and stereoselectivity

The addition of primary and secondary aliphatic amines to glycal-derived allyl epoxides is completely 1,2-regio- and anti-stereoselective, whereas mixtures of the corresponding anti-1,2- [3-N-(substituted-amino) glycals] and anti-1,4-addition products (N-glycosyl amines) are obtained with N-(mesyl)-aziridines. In this way, structural moieties, otherwise difficult to synthesize, are obtained by means of a very simple protocol. The regio- and stereoselectivity observed with epoxides is the consequence of an isomerization process, whereas the result obtained with aziridines is explained by the absence of an effective substrate-nucleophile (amine) coordination.     

Asymmetric synthesis of (S)-vigabatrin and (S)-dihydrokavain via cobalt catalyzed hydrolytic kinetic resolution of epoxides

A concise route to the asymmetric synthesis of (S)-vigabatrin^® and (S)-dihydrokavain has been described using Co-catalyzed hydrolytic kinetic resolution of racemic epoxides and regiospecific opening of terminal epoxides with dimethylsulfonium methylide as the key steps.     

Reactions of epoxides derived from internal perfluoroolefins with o-phenylenediamine and 2-aminophenol

The reactions of epoxy derivatives of internal perfluoroolefins with o-phenylenediamine and 2-aminophenol in dioxane gave 23–67% of the corresponding 2,3-bis(perfluoroalkyl)quinoxalines and 2,3-bis(perfluoroalkyl)-2H-1,4-benzoxazin-2-ols, respectively. When N,N-dimethylacetamide was used as a solvent, the main reaction pathway was anionic isomerization of epoxides into ketones which were then converted into 2-perfluoroalkylbenzimidazoles (in the reactions with o-phenylenediamine) or 2-hydroxy-N-perfluoroalkanoylanilines (in the reactions with 2-aminophenol). The reaction of 3,4-epoxydodecafluorohexane with 2-aminophenol in N,N-dimethylacetamide was accompanied by unusual cyclization to afford 2-pentafluoropropanoyl-2-pentafluoroethyl-1,3-benzoxazolidine.     

N-Bromosuccinimide-dibenzoyl peroxide/azabisisobutyronitrile: a reagent for Z- to E-alkene isomerization

N-Bromosuccinimide-dibenzoyl peroxide/azobisisobutyronitrile is used to carry out several types of Z- to E-alkene isomerizations. The NBS-bromination conditions are sufficient for both allylic bromination and alkene isomerization. When the allylic hydrogens are not available in substrates, only the isomerization of the alkene takes place. The present conditions for isomerization of carbon-carbon double bonds are mild and efficient.     

E/Z Isomerization of 3,3-disubstituted allylic thioethers

Allylic thioethers of the general structure 1 underwent E/Z isomerization during both basic and acidic hydrolysis of the ester moiety at the remote end of the molecule. The isomerization was dependent on the substitution of the allylic moiety. The presence of a 5-membered heterocycle on the double bond supported the isomerization. However, analogous oxy-ethers were stable.     

Highly selective isomerization of N-allylamides and N-allylamines

A highly selective rhodium and ruthenium catalyzed transformation of N-allylamines and N-allylamides to the corresponding 1-propenyl derivatives is described. Strong E-selectivity in the isomerization of allylamines was observed. The first catalytic system containing a transition metal complex for Z-selective isomerization of allylamides is presented. An application of siliceous mesoporous cellular foams for effective removal of the catalyst from the post-reaction mixture is described.     

The use of trans-2,3-divinyl epoxides as precursors to carbonyl ylides

trans-2,3-Divinyl epoxides have been found to be good substrates for the generation of carbonyl ylides in CCl₄ and 145 °C. These ylides, to a limited extent, undergo isomerization to cis-2,3-divinyl epoxides, leading to the isolation of 4,5-dihydrooxepins. Of greater potential usefulness is the finding that these ylides can be efficiently trapped in an intermolecular sense by a dipolarophile, leading to dihydrofurans.     

Concise synthesis of β-blockers (S)-metoprolol and (S)-betaxolol using hydrolytic kinetic resolution

Enantiopure (S)-metoprolol and (S)-betaxolol were prepared in an extremely simple and practical way using Jacobsen's hydrolytic kinetic resolution of terminal epoxides in isopropanol.     

Reactions of N - and C -alkenylanilines: VIII. Synthesis of functionalized cycloalka[ b ]indoles from o -(cycloalk-2-en-1-yl)anilines

N-Acyl-2-(cyclohex-2-en-1-yl)anilines react with molecular iodine to give the corresponding N-acyl-1-iodo-1,2,3,4,4a,9a-hexahydrocarbazoles which undergo isomerization into 1-R-2a,3,4,5,5a,10a-hexahydro[1,3]oxazolo[5,4,3-j,k]carbazol-10-ium iodides; no isomerization occurs with N-acetyl-3-iodo1,2,3,3a,4,8b-hexahydrocyclopenta[b]indole. The reaction of N-p-tolylsulfonyl-3,4,4a,9a-tetrahydrocarbazoles with hydrogen peroxide leads to the formation of a single 1,2-epoxy derivative with trans orientation of the nitrogen-and oxygen-containing rings. N-p-Tolylsulfonyl-1,3a,4,8b-tetrahydrocyclopenta[b]indoles give rise to the corresponding 2,3-epoxy derivatives with both trans and cis orientation of the dihydropyrrole and oxirane fragments. The resulting epoxides undergo trans-opening with formation of N-p-tolylsulfonyl-1-hydroxy-2-methoxy-1,2,3,4,4a,9a-hexahydrocarbazoles and N-p-tolylsulfonyl-3-hydroxy-2-methoxy-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indoles on heating in methanol in the presence of KU-2 cation exchanger. Mutual orientation of the oxirane and nitrogen-containing rings in the epoxides derived from cyclopenta[b]-indoles was proved by X-ray analysis. Original Russian Text ? R.R. Gataullin, N.A. Likhacheva, K.Yu. Suponitskii, I.B. Abdrakhmanov, 2007, published in Zhurnal Organicheskoi Khimii, 2007, Vol. 43, No. 9, pp. 1316–1326. For communication VII, see [1].     

The isomerization of cis,trans-1,5-cyclodecadiene by RhCl3 · 3H2O in ethanol

The isomerization of cis,cis-1,6-cyclodecadiene to cis,trans-1,5-; and cis,cis-1,5-cyclodecadiene in the presence of their rhodium complexes seems to indicate an isomerization for which no thermal conversion has been reported. Evidences are presented for the functioning of ethanol as a hydride source in these polymerizations.     

Substrate specificity and reaction mechanism of recombinant styrene oxide isomerase from Pseudomonas putida S12

To clarify the substrate specificity of the recombinant styrene oxide isomerase, various epoxides were subjected to the reaction. From the substituent effect on the rate of isomerization, the mechanism of the isomerase catalyzed reaction was estimated.     

Hydrogénolyse en phase liquide sur Pd/C des époxydes du carvomenthène et du limonène

Hydrogenolysis over Pd/C of cis and trans epoxides of carvomenthene and limonene give a mixture of hydrocarbons, secondary and tertiary alcohols, and ketones in proportions dependent upon the nature of the starting material. In the limonene epoxides, the extracyclic double bond plays an important role in the opening of the oxirane ring through a common unsaturated tertiary alcohol intermediate by double bond migration, hydrogenation of which leads to the products. For the carvomenthene epoxides the results are similar to those found in the 4-t-butyl series with competition between cis addition and trans addition of hydrogen. The presence of the isopropenyl group leads to slower reaction rates in comparison with t-butyl analogues.     

Synthesis of complex carbobicyclic compounds from sugar allyltins: functionalization of the allylic position in bicyclo[4.3.0]nonene derivatives

Two approaches for the functionalization of the allylic position in 7,8,9-tri-O-benzyl-5-substituted bicyclo[4.3.0]non-2-ene derivative 12 were examined. The first method, which involves an epoxidation of the C2–C3 double bond followed by a base induced isomerization, was found to be inappropriate. Although the epoxides were formed in good yields, the base-induced isomerization of the latter performed under the harsh conditions (LDA, HMPA, 80 °C) did not lead to the desired allylic alcohol 13, but to the tricyclic derivative 15 resulting from the opening of the oxirane ring by the anion generated from the benzyl group at the C9-position. The other, more promising approach, consisted of the cis-hydroxylation of the C2–C3 double bond followed by selective protection of one of the hydroxyl groups (at the C2-position) using the dibutyltin methodology. The free hydroxyl group located at the C3 position can be eventually eliminated to give the desired olefin with the double bond between the C3 and C4 carbon atoms of the bicyclic system.     

Investigation of the catalytic activity of an electron-deficient vanadium(IV) tetraphenylporphyrin: A new, highly efficient and reusable catalyst for ring-opening of epoxides

In this work, the catalytic activity of high-valent tetraphenylporphyrinatovanadium(IV) trifluoromethanesulfonate, [V^IV(TPP)(OTf)₂], in the nucleophilic ring-opening of epoxides is reported. This new V(IV) catalyst was used as an efficient catalyst for alcoholysis with primary (methanol, ethanol and n-propanol), secondary (iso-propanol) and tertiary alcohols (tert-butanol), hydrolysis and acetolysis of epoxides with acetic acid and also for the conversion of epoxides to 1,2-diacetates with acetic anhydride, conversion of epoxides to thiiranes with ammonium thiocyanate and thiourea, and for conversion of epoxides to acetonides with acetone. The catalyst was reused several times without loss of its activity.     

Synthesis of the enantiomeric forms of cis and trans 1-benzyloxy-2,3-epoxy butane and of (3S,4S) 4-methyl-3-heptanol

The C₄erythro and threo diols (7) and (8) are converted either into the chiral epoxides (13) and (15) or into the enantiomers (14) and (16); the epoxide (13) is used as chiral synthon for the preparation of (3$\text{S}$,4$\text{S}$) 4-methyl-3-heptanol (21).     

Direct conversion of epoxides to vic-difluorides

vic-Difluoro compounds can be directly prepared from epoxides by reaction with Et₃N-3HF and DFMBA under microwave-irradiation conditions.     

Synthesis of carba analogs of 6-O-(benzyl)-d-allal- and -d-galactal-derived allyl epoxides and evaluation of the regio- and stereoselective behavior in nucleophilic addition reactions

The new racemic diastereoisomeric epoxides 6α and 6β, the carba analogs of the corresponding d-galactal- and d-allal-derived allyl epoxides have been synthesized and their regio- and stereoselective behavior examined in addition reactions with model O-, C-, N-, and S-nucleophiles. The results have indicated that epoxide 6β has a pronounced tendency toward anti-1,2-addition, whereas epoxide 6α shows interesting levels of syn- and/or anti-1,4-addition processes. A chiral recognition process found with epoxide 6β, turned out to be consistently reduced in epoxide 6α. All the results have been rationalized on the basis of conformational, steric, and stereoelectronic effects.     

H4SiW12O40-catalyzed cyclization of epoxides/aldehydes and sulfonyl hydrazides: An efficient synthesis of 3,4-disubstituted 1H-pyrazoles

A simple and efficient method for the synthesis of pyrazoles through a silicotungstic acid(H₄Si W₁₂O₄₀)-catalyzed cyclization of epoxides/aldehydes and sulfonyl hydrazides has been developed. Various epoxides/aldehydes were smoothly reacted with sulfonyl hydrazides to furnish regioselectivity 3,4-disubstituted 1H-pyrazoles. The application of such an earth-abundant, readily accessible, and nontoxic catalyst provides a green approach for the construction of 3,4-di...     

α-Lithiation-rearrangement of N-toluenesulfonyl aziridines with sec-butyllithium and (−)-sparteine: opposite sense of asymmetric induction to epoxides

The α-lithiation rearrangement of three cyclic N-toluenesulfonyl (tosyl) aziridines has been carried out using sec-butyllithium/(−)-sparteine. In each case, it was established that preferential lithiation of the S-aziridine stereocentre occurred. This is the opposite sense of asymmetric induction to that observed with epoxides.     

Synthesis of (±)-2R,4R,5S-2-methoxy-4-nitro-5-(2,3,4-trimethoxyphenyl)cyclohexanone and (±)-2R,4S,5R-2-methoxy-5-nitro-4-(2,3,4-trimethoxyphenyl)cyclohexanone as colchicine mimetics

Colchicine mimetic (±)-4S,5R-4-nitro-5-(2,3,4-trimethoxyphenyl)cyclohexene (1) was epoxidized to afford a mixture of epoxides. The epoxides were separately converted in two steps, with high stereoselectivity, to two regioisomeric α-methoxyketones. One regioisomer, (±)-2R,4S,5R-2-methoxy-5-nitro-4-(2,3,4-trimethoxyphenyl)cyclohexanone (17), proved to be about 12-fold more potent than synthetic precursor 1 against HCT-116 tumor cells while the other regioisomer, (±)-2R,4R,5S-2-methoxy-4-nitro-5-(2,3,4-trimethoxyphenyl)cyclohexanone (16), and the synthetic intermediates tested showed no improvement in potency.