Highly regioselective ring opening of epoxides and aziridines using (bromodimethyl)sulfonium bromide

Epoxides and aziridines undergo ring opening efficiently with (bromodimethyl)sulfonium bromide at room temperature to form the corresponding β-bromohydrins and β-bromoamines, respectively. The conversions are highly regioselective and afford the products in excellent yields within a short period of time.     

Unexplored nucleophilic ring opening of aziridines

The reactivity of dianions of carboxylic acids towards aziridines has been studied. Although, a similar reactivity to that of enolates from ketones, esters or amides has been observed, the method directly yields γ-aminoacids in one step. The method is complementary of previous results of enenediolate reactivity with other electrophiles. A comparative study with the reactivity of this enediolates with epoxides is included.     

Regio- and stereoselective ring opening of enantiomerically enriched 2-aryl oxetanes and 2-aryl azetidines with aryl borates

The regioselective ring opening of 2-aryl-substituted four-membered heterocyclic rings with phenols, including catechol, was achieved by the use of aryl borates in mild and neutral reaction conditions without the aid of any transition metal catalysts. While N-alkyl azetidines were found not to be reactive, optically active N-tosyl azetidines gave the corresponding beta-aryloxy amines in a racemic form, thus indicating the considerable carbocationic character of the transition state. The introduction of a hydroxyl group in the azetidine ring (i.e., an azetidinol), able to anchor the aryl borate and to direct the subsequent nucleophilic delivery, was shown to determine the ring-opening process with predominant inversion of configuration. When enantiomerically enriched 2-aryl oxetanes were used, the reduced extent of racemization observed (up to 93:7 er) was rationalized by an intramolecular delivery through a six-membered transition state, giving beta-aryloxy alcohols with a predominant retention of configuration (i.e., a syn-stereoselective ring opening). The aryloxy alcohols obtained, endowed with suitable functionalities, can be cyclized to give access to enantiomerically enriched 2-aryl-1,5-benzodioxepins.     

Tri-n-butylphosphane catalyzed ring opening of aziridines with secondary amines

Ring opening of aziridine with dialkyl amine took place readily in the presence of catalytic amounts of tri-n-butylphosphane （10 mol%） in the mixture of CH₃CN/H₂O（10:1）,giving corresponding vicinal diamines in mediate to high yields（58-95%） with good regioselectivitie,while aromatic secondary amine could not react under the same conditions.Tri-n-butylphosphane exhibited different catalytic selectivity to amines from Lewis acid catalysts.     

Regio- and stereoselective ring opening of aziridines with nitric oxide

Reaction of N-tosyl aziridines with nitric oxide affords the corresponding ring-opened products in regio-, stereoselectivities and excellent yields.     

Zirconyl nitrate mediated regioselective ring opening of epoxides and aziridines: an easy synthesis of β-nitrato-alcohols and -sulfonamides

Epoxides and aziridines are cleaved efficiently and regioselectively in the presence of zirconyl nitrate at room temperature to afford the corresponding β-nitrato-alcohols and -sulfonamides, respectively, in high yields.     

Lewis base catalyzed ring opening of aziridines with silylated nucleophiles

The ring opening of N-tosylaziridines with trimethylsilylated nucleophiles, catalyzed by N,N,N',N'-tetramethylethylenediamine, led to the production of beta-functionalized sulfonamides in good to excellent yields with high regioselectivity. [reaction: see text]     

Solvent-free direct regioselective ring opening of epoxides with imidazoles

The reaction of different epoxides with commercially available imidazole at 60 °C leads to the formation of the corresponding 1-(β-hydroxyalkyl)imidazoles in a regioselective manner. When the reaction is applied to a chiral epoxide [(R)-styrene oxide], the expected chiral alcohol is isolated with the same enantiomeric excess. The use of benzimidazole as the heterocyclic component in the same process also allows the simple preparation of the corresponding 1-(β-hydroxyalkyl)benzimidazoles.     

Regioselectivity in the ring opening of non-activated aziridines

In this critical review, the ring opening of non-activated 2-substituted aziridines via intermediate aziridinium salts will be dealt with. Emphasis will be put on the relationship between the observed regioselectivity and inherent structural features such as the nature of the C2 aziridine substituent and the nature of the electrophile and the nucleophile. This overview should allow chemists to gain insight into the factors governing the regioselectivity in aziridinium ring openings (81 references).     

Rhodium-catalyzed ring opening of vinyl epoxides with alcohols and aromatic amines

[Rh(CO)(2)Cl](2) is an effective catalyst for the ring opening of vinyl epoxides with alcohols and aromatic amines under neutral conditions at room temperature. The reaction occurs with excellent diastereo- and regioselectivity (>20:1) giving the trans-1,2-amino alcohols or alkoxy alcohols for a wide range of substrates. The regio- and stereochemistry of these reactions is complementary to that typically obtained with palladium-catalyzed ring openings of vinyl epoxides.     

Studies of rhodium-catalyzed ring opening of vinyl epoxides

The stereoselective 6-endo mode cyclization of vinyl epoxides has been achieved by the use of a catalytic amount of [Rh(CO)₂Cl]₂ affording six-membered heterocycle systems, such as piperidines and tetrahydropyrans. The scope and limitations of the reaction are discussed.     

PPh3/halogenating agent-mediated highly efficient ring opening of activated and non-activated aziridines

We report here the use of PPh₃/halogenating agents as highly efficient reagents for the ring opening of aziridines with halides. The method works effectively for both activated and non-activated aziridines, and furnishes the products in excellent yields within a short period of time.     

Antimony(III) chloride-catalyzed ring opening of epoxides with anilines

A mild and convenient ring opening of epoxides with aniline and its derivatives takes place at room temperature in the presence of antimony trichloride as catalyst to afford the corresponding β-amino alcohols in good yields.     

Azacycloalkanes from epoxides and aziridines

Methods of preparation of azetidines, pyrrolidines, and piperidines from epoxides and aziridines were analyzed. The possibility of epoxides conversion into aziridines was considered. The examples of application of azacycloalkanes in the medical and organic chemistry as biologically active substances and synthons for their preparation were calculated.     

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.     

Regioselective ring opening of aziridines with activated DMF complexes: a facile synthesis of β-haloamines

A wide variety of aziridines were converted to the corresponding β-haloamines using activated DMF complexes in good to excellent yields with high regioselectivity.     

Sulfamic acid catalyzed ring opening of epoxides with amines under solvent-free conditions

Sulfamic acid (SA) catalyses the nucleophilic opening of epoxide rings by amines leading to the efficient synthesis of ß-amino alcohols. The reaction works well with aromatic and aliphatic amines in short reaction times and in the absence of solvent. Exclusive trans stereoselectivity is observed for the ring opening of cyclohexene oxide. This method exhibits excellent regioselectivity for preferential nucleophilic attack at the less hindered position during the reaction with unsymmetrical epoxides.     

Reductive opening of aziridines with polymethylhydrosiloxane

Regio and chemoselective reductive opening of aziridines is achieved using catalytic palladium on charcoal and polymethylhydrosiloxane (PMHS) as a soluble hydrogen source.