The Origin of Chemical and Configurational Stability of Chiral Nonracemic tert-Butyl Aziridinecarboxylate Anions

Abstract

Keywords: Aziridine / Configurational stability / Nitrogen inversion / Kinetic acidity / Quaternary amino estersThe origin of good chemical and configurational stability of aziridine ester anions derived from (R)-(−)-phenylglycinol has been investigated. Kinetic acidity seems to play an important role in the deprotonation step and chemical stability of the anionic species. Spectroscopic investigations showed

Direct Access to N-H-Aziridines from Asymmetric Catalytic Aziridination with Borate Catalysts Derived from Vaulted Binaphthol and Vaulted Biphenanthrol Ligands

“…Trisubstituted aziridine 27 was prepared from aziridine 15d by a highly diastereoselective alkylation. The alkylation of aziridine-2-carboxylates is a rare event, which had previously been observed only under special circumstances . However, we recently reported that this process is quite general for N -benzhydryl-substituted aziridines, where the steric bulk of this group apparently blocks the normally predominant Claisen condensation pathway 7d.…”

Direct Access to N-H-Aziridines from Asymmetric Catalytic Aziridination with Borate Catalysts Derived from Vaulted Binaphthol and Vaulted Biphenanthrol Ligands

“…Trisubstituted aziridine 27 was prepared from aziridine 15d by a highly diastereoselective alkylation. The alkylation of aziridine-2-carboxylates is a rare event, which had previously been observed only under special circumstances . However, we recently reported that this process is quite general for N -benzhydryl-substituted aziridines, where the steric bulk of this group apparently blocks the normally predominant Claisen condensation pathway 7d.…”

Synthesis and Reactivity of 2-(Carboxymethyl)aziridine Derivatives

“…When aziridine ester (2 R )- 201 was treated under analogous reaction conditions (LDA, THF, −78 °C), only self-condensation was observed. , Since intramolecular stabilization appeared to be negligible in this compound, the highly reactive lithiated intermediate was stabilized by intermolecular chelation in a more suitable solvent system. When a 5:1 mixture of DME:Et 2 O was used, a more stabilized aziridine carboxylate anion was formed, which reacted with compound 202 to give aziridine (2 R ,1′ R )- 203 in a low yield (30%) but with excellent retention of configuration (Scheme ). , …”

Unnatural amino acids. 3. Aziridinyl ketones from esters and amides of aziridine-2-carboxylic acids

“…In 1997 Vedejs published a paper on lithiated complexes of aziridines with BH 3 [6]. It was shown that the increased s-character of the CH bonds in the aziridine ring accelerated lithiation in position 2 of the aziridine ring, facilitating the reaction with electrophiles.The stability of carbanions in a series of esters of aziridine-2-carboxylic acids has been demonstrated recently [7,8]. A methoxymethyl protecting group on the aziridine nitrogen atom stabilizes the intermediate carbanion and permits the preparation of a series of 2-substituted esters of aziridine-2-carboxylic acids [8].…”

Direct Access to N-H-Aziridines from Asymmetric Catalytic Aziridination with Borate Catalysts Derived from Vaulted Binaphthol and Vaulted Biphenanthrol Ligands

“…Trisubstituted aziridine 27 was prepared from aziridine 15d by a highly diastereoselective alkylation. The alkylation of aziridine-2-carboxylates is a rare event, which had previously been observed only under special circumstances . However, we recently reported that this process is quite general for N -benzhydryl-substituted aziridines, where the steric bulk of this group apparently blocks the normally predominant Claisen condensation pathway 7d.…”

Synthesis and Reactivity of 2-(Carboxymethyl)aziridine Derivatives

“…When aziridine ester (2 R )- 201 was treated under analogous reaction conditions (LDA, THF, −78 °C), only self-condensation was observed. , Since intramolecular stabilization appeared to be negligible in this compound, the highly reactive lithiated intermediate was stabilized by intermolecular chelation in a more suitable solvent system. When a 5:1 mixture of DME:Et 2 O was used, a more stabilized aziridine carboxylate anion was formed, which reacted with compound 202 to give aziridine (2 R ,1′ R )- 203 in a low yield (30%) but with excellent retention of configuration (Scheme ). , …”

Unnatural amino acids. 3. Aziridinyl ketones from esters and amides of aziridine-2-carboxylic acids

“…In 1997 Vedejs published a paper on lithiated complexes of aziridines with BH 3 [6]. It was shown that the increased s-character of the CH bonds in the aziridine ring accelerated lithiation in position 2 of the aziridine ring, facilitating the reaction with electrophiles.The stability of carbanions in a series of esters of aziridine-2-carboxylic acids has been demonstrated recently [7,8]. A methoxymethyl protecting group on the aziridine nitrogen atom stabilizes the intermediate carbanion and permits the preparation of a series of 2-substituted esters of aziridine-2-carboxylic acids [8].…”

Direct Access to N-H-Aziridines from Asymmetric Catalytic Aziridination with Borate Catalysts Derived from Vaulted Binaphthol and Vaulted Biphenanthrol Ligands

“…Trisubstituted aziridine 27 was prepared from aziridine 15d by a highly diastereoselective alkylation. The alkylation of aziridine-2-carboxylates is a rare event, which had previously been observed only under special circumstances . However, we recently reported that this process is quite general for N -benzhydryl-substituted aziridines, where the steric bulk of this group apparently blocks the normally predominant Claisen condensation pathway 7d.…”

Synthesis and Reactivity of 2-(Carboxymethyl)aziridine Derivatives

“…When aziridine ester (2 R )- 201 was treated under analogous reaction conditions (LDA, THF, −78 °C), only self-condensation was observed. , Since intramolecular stabilization appeared to be negligible in this compound, the highly reactive lithiated intermediate was stabilized by intermolecular chelation in a more suitable solvent system. When a 5:1 mixture of DME:Et 2 O was used, a more stabilized aziridine carboxylate anion was formed, which reacted with compound 202 to give aziridine (2 R ,1′ R )- 203 in a low yield (30%) but with excellent retention of configuration (Scheme ). , …”

Unnatural amino acids. 3. Aziridinyl ketones from esters and amides of aziridine-2-carboxylic acids

“…In 1997 Vedejs published a paper on lithiated complexes of aziridines with BH 3 [6]. It was shown that the increased s-character of the CH bonds in the aziridine ring accelerated lithiation in position 2 of the aziridine ring, facilitating the reaction with electrophiles.The stability of carbanions in a series of esters of aziridine-2-carboxylic acids has been demonstrated recently [7,8]. A methoxymethyl protecting group on the aziridine nitrogen atom stabilizes the intermediate carbanion and permits the preparation of a series of 2-substituted esters of aziridine-2-carboxylic acids [8].…”