A new approach towards 2-amino-1-aryloxy-3-methoxypropanes from 1-arylmethyl-2-(bromomethyl)aziridines

Cobalt carbonyl-catalyzed carbonylation of functionalized aziridines to versatile β-lactam building blocks

Aziridine to azetidin-2-one carbonylation as a convenient entry to pyrrolidines,C-fused bi- and tricyclic β-lactams and monocyclic carbapenem analogs.

Synthetic route to chiral indolines via ring-opening/C-N cyclization of activated 2-haloarylaziridines

A practical approach for the synthesis of 3-substituted indolines via regio- and stereoselective SN2-type ring-opening of 2-(2-halophenyl)-N-tosylaziridines with heteroatomic nucleophiles (O, N, and S) followed by palladium-catalyzed intramolecular C-N cyclization is reported in excellent yields (up to >99%) and enantiomeric excess (ee 99%).

Synthetic route to chiral tetrahydroquinoxalines via ring-opening of activated aziridines

A highly regio- and stereoselective route for the synthesis of racemic and nonracemic tetrahydroquinoxalines via the S(N)2-type ring-opening of activated aziridines with 2-bromoanilines followed by the Pd-catalyzed intramolecular C-N bond formation is described.

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).

Opposite regiospecific ring opening of 2-(cyanomethyl)aziridines by hydrogen bromide and benzyl bromide: experimental study and theoretical rationalization

Ring opening of 1-arylmethyl-2-(cyanomethyl)aziridines with HBr afforded 3-(arylmethyl)amino-4-bromobutyronitriles via regiospecific ring opening at the unsubstituted aziridine carbon. Previous experimental and theoretical reports show treatment of the same compounds with benzyl bromide to furnish 4-amino-3-bromobutanenitriles through ring opening at the substituted aziridine carbon. To gain insights into the regioselective preference with HBr, reaction paths have been analyzed with computational methods. The effect of solvation was taken into account by the use of explicit solvent molecules. Geometries were determined at the B3LYP/6-31++G(d,p) level of theory, and a Grimme-type correction term was included for long-range dispersion interactions; relative energies were refined with the meta-hybrid MPW1B95 functional. Activation barriers confirm preference for ring opening at the unsubstituted ring carbon for HBr. HBr versus benzyl bromide ring opening was analyzed through comparison of the electronic structure of corresponding aziridinium intermediates. Although the electrostatic picture fails to explain the opposite regiospecific nature of the reaction, frontier molecular orbital analysis of LUMOs and nucleophilic Fukui functions show a clear preference of attack for the substituted aziridine carbon in the benzyl bromide case and for the unsubstituted aziridine carbon in the HBr case, successfully rationalizing the experimentally observed regioselectivity.

Synthesis of stereodefined piperidines from aziridines and their transformation into conformationally constrained amino acids, amino alcohols and 2,7-diazabicyclo[3.3.1]nonanes

2-(2-Cyano-2-phenylethyl)aziridines were converted into novel cis- and trans-2-chloromethyl-4-phenylpiperidine-4-carbonitriles via alkylation with 1-bromo-2-chloroethane followed by microwave-assisted 6-exo-tet cyclization and regiospecific ring opening. The latter piperidines were used as eligible substrates for the synthesis of stereodefined 2-chloromethyl-, 2-hydroxymethyl-, and 2-carboxymethyl-4-phenylpiperidine-4-carboxylic acids, 2-hydroxymethyl-4-phenylpiperidine-4-carbonitriles, 3-hydroxy-5-phenylazepane-5-carbonitriles, and 5-phenyl-2,7-diazabicyclo[3.3.1]nonanes.

Nucleophile-dependent regioselective ring opening of 2-substituted N,N-dibenzylaziridinium ions: bromide versus hydride

The ring opening of 2-substituted N,N-dibenzylaziridinium ions by bromide exclusively occurs at the substituted aziridine carbon atom in a stereospecific way, whereas the opposite regioselectivity was observed for hydride-induced ring opening at the unsubstituted position; furthermore, this unprecedented hydride-promoted reactivity was validated by means of Density Functional Theory (DFT) calculations.

Reactivity of N-(omega-haloalkyl)-beta-lactams with regard to lithium aluminium hydride: novel synthesis of 1-(1-aryl-3-hydroxypropyl)aziridines and 3-aryl-3-(N-propylamino)propan-1-ols

The reactivity of 4-aryl-1-(2-chloroethyl)azetidin-2-ones and 4-aryl-1-(3-bromopropyl)azetidin-2-ones with regard to lithium aluminium hydride has been evaluated for the first time. 4-Aryl-1-(2-chloroethyl)azetidin-2-ones were transformed into novel 1-(1-aryl-3-hydroxypropyl)aziridines through an unprecedented conversion of beta-lactams into 2,3-unsubstituted aziridine derivatives. Unexpectedly, 4-aryl-1-(3-bromopropyl)azetidin-2-ones underwent dehalogenation towards 3-aryl-3-(N-propylamino)propan-1-ols upon treatment with LiAlH(4). 1-(1-Aryl-3-hydroxypropyl)aziridines were further elaborated by means of ring opening reactions using benzyl bromide in acetonitrile towards 3-aryl-3-[N-benzyl-N-(2-bromoethyl)amino]propan-1-ols and using aluminium(iii) chloride in diethyl ether, affording 3-aryl-3-[N-(2-chloroethyl)amino]propan-1-ols.

Synthesis of 1-Arylmethyl-2-(2-cyanoethyl)aziridines and Their Rearrangement into Novel 2-(Aminomethyl)cyclopropanecarbonitriles

1-Arylmethyl-2-(bromomethyl)aziridines were transformed into novel 2-(2-cyanoethyl)aziridines upon treatment with alpha-lithiated trimethylsilylacetonitrile in THF in an efficient and straightforward approach. The latter aziridines underwent ring opening by reaction with benzyl bromide in acetonitrile, affording 5-amino-4-bromopentanenitriles through a regiospecific ring opening of intermediate aziridinium salts by bromide. Further elaboration of these gamma-bromonitriles resulted in the synthesis of novel 2-[N,N-bis(arylmethyl)aminomethyl]cyclopropanecarbonitriles in high yields by means of a 1,3-cyclization protocol upon treatment with KOtBu in THF.

Novel Synthesis of 3,4-Diaminobutanenitriles and 4-Amino-2-butenenitriles from 2-(Cyanomethyl)aziridines through Intermediate Aziridinium Salts: An Experimental and Theoretical Approach

1-Arylmethyl-2-(cyanomethyl)aziridines were transformed into 4-(N,N-bis(arylmethyl)amino)-3-(pyrrolidin-1-yl)butanenitriles and 4-(N,N-bis(arylmethyl)amino)-2-butenenitriles via 4-(N,N-bis(arylmethyl)amino)-3-bromobutanenitriles in high yields and purity. The key steps involve the unprecedented regiospecific ring opening of intermediate 2-(cyanomethyl)aziridinium salts by bromide and pyrrolidine in acetonitrile, exclusively at the substituted aziridine carbon atom. The results were rationalized on the basis of ab initio calculations.

Highly unusual conversion of 1-alkyl-2-(bromomethyl)aziridines into 1-alkyl-2-(N-alkyl-N-ethylaminomethyl)aziridines using methyllithium

1-alkyl-2-(bromomethyl)aziridines were transformed into 1-alkyl-2-(N-alkyl-N-ethylaminomethyl)aziridines upon treatment with 2-3 equiv. of methyllithium in THF or Et(2)O; the peculiarity in this transformation comprises the presence of an N-ethyl group in the end-products as well as the total number of carbon atoms, resulting from a highly unusual reaction course with a novel S(N)2'-type substitution at the aziridine moiety and liberation of acetylene from an intermediate vinylamine as the key reaction steps.

Novel Synthesis of cis-3,5-Disubstituted Morpholine Derivatives

1-tert-Butyl-2-(allyloxymethyl)aziridine has been transformed for the first time diastereoselectively into cis-3,5-di(bromomethyl)-4-tert-butylmorpholine via an electrophile-induced ring closure using bromine in dichloromethane. The latter morpholine has been used as a substrate for the synthesis of the corresponding 3,5-di(methoxymethyl)morpholine and 3,5-di(cyanomethyl)morpholine upon nucleophilic displacement of both bromo atoms. Further evaluation of this protocol toward the synthesis of 4-arylmethyl- and 4-alkylmethyl-3,5-di(bromomethyl)morpholines showed that the premised cyclization of the corresponding 2-(allyloxymethyl)aziridines into 3,5-di(bromomethyl)morpholines only proceeded well for the N-neopentylmorpholine, which was subsequently transformed into a 3-oxa-7-thia-9-azabicyclo[3.3.1]nonane derivative. Also, in some other cases, the desired 3,5-di(bromomethyl)morpholines were isolated in low yields and transformed into the corresponding 3,5-di(cyanomethyl)morpholines.

Synthesis of 1-Arylmethyl-2-(cyanomethyl)aziridines and Their Ring Transformation into Methyl N-(2-Cyanocyclopropyl)benzimidates

1-Arylmethyl-2-(cyanomethyl)aziridines were prepared in high yields from the corresponding 2-(bromomethyl)aziridines upon treatment with potassium cyanide in DMSO. Ring opening of the aziridine moiety with N-chlorosuccinimide in CCl4 and subsequent treatment of the thus formed 4-chloro-3-(N-chloro-N-(alpha,alpha-dichlorobenzyl)amino)butanenitriles with sodium methoxide in methanol resulted in novel methyl N-(2-chloro-1-(cyanomethyl)ethyl)benzimidates, although in low yields. The latter gamma-chloro nitriles were smoothly converted into methyl N-(2-cyanocyclopropyl)benzimidates as precursors of biologically relevant beta-ACC derivatives through a 1,3-cyclization protocol by reaction with potassium tert-butoxide in THF.