Generation and Ring Opening of Aziridines in Telescoped Continuous Flow Processes

A simple method for the preparation of a variety of <i>N</i>-sulfonyl aziridines (10 examples) from 1,2-amino alcohols under continuous flow conditions is described. Using flow based methods, the aziridines can be further ring opened with oxygen, carbon, and halide nucleophiles or ring expanded to imidazolines by Lewis acid promoted reaction with nitriles. Telescoping the aziridine generation and ring opening steps together in a microfluidic reactor allows the chemistry to be undertaken with limited exposure to the potentially hazardous aziridine intermediates

Generation and Ring Opening of Aziridines in Telescoped Continuous Flow Processes

A simple method for the preparation of a variety of <i>N</i>-sulfonyl aziridines (10 examples) from 1,2-amino alcohols under continuous flow conditions is described. Using flow based methods, the aziridines can be further ring opened with oxygen, carbon, and halide nucleophiles or ring expanded to imidazolines by Lewis acid promoted reaction with nitriles. Telescoping the aziridine generation and ring opening steps together in a microfluidic reactor allows the chemistry to be undertaken with limited exposure to the potentially hazardous aziridine intermediates

Palladium-Catalyzed Multicomponent Synthesis of 2‑Aryl-2-imidazolines from Aryl Halides and Diamines

An efficient palladium-catalyzed three-component reaction that combines aryl halides, isocyanides, and diamines provides access to 2-aryl-2-imidazolines in yields up to 96%. Through variation of the diamine component, the reaction can be extended to the synthesis of 2-aryl-1<i>H</i>-benzimidazoles and 2-aryl-1,4,5,6-tetrahydropyrimidines

Palladium-Catalyzed Multicomponent Synthesis of 2‑Aryl-2-imidazolines from Aryl Halides and Diamines

An efficient palladium-catalyzed three-component reaction that combines aryl halides, isocyanides, and diamines provides access to 2-aryl-2-imidazolines in yields up to 96%. Through variation of the diamine component, the reaction can be extended to the synthesis of 2-aryl-1<i>H</i>-benzimidazoles and 2-aryl-1,4,5,6-tetrahydropyrimidines

Asymmetric Synthesis of 2‑Substituted Oxetan-3-ones via Metalated SAMP/RAMP Hydrazones

2-Substituted oxetan-3-ones can be prepared in good yields and enantioselectivities (up to 84% ee) by the metalation of the SAMP/RAMP hydrazones of oxetan-3-one, followed by reaction with a range of electrophiles that include alkyl, allyl, and benzyl halides. Additionally, both chiral 2,2- and 2,4-disubstituted oxetan-3-ones can be made in high ee (86–90%) by repetition of this lithiation/alkylation sequence under appropriately controlled conditions. Hydrolysis of the resultant hydrazones with aqueous oxalic acid provides the 2-substituted oxetan-3-ones without detectable racemization

Nitrogen Stereodynamics and Complexation Phenomena as Key Factors in the Deprotonative Dynamic Resolution of Alkylideneaziridines: A Spectroscopic and Computational Study

The present work is aimed at shedding light on the origin of the stereoselectivity observed in the reactions of chiral heterosubstituted organolithiums, generated by lithiation of alkylideneaziridines. Factors such as the nitrogen inversion barrier, the stereochemistry at the nitrogen atom, the substitution pattern of the alkylideneaziridines, and the reaction conditions are taken into consideration. The interplay between nitrogen stereodynamics and complexation phenomena seems to be crucial in determining the stereochemical outcome of the lithiation/trapping sequence. The findings were rationalized by a synergistic use of NMR experiments, run on the lithiated intermediates, alongside computational data. It has been demonstrated that, in such systems, the stereochemistry-determining step is the deprotonation reaction, and a model based on a deprotonative dynamic resolution has been proposed. Such findings could find application in dynamic systems other than aziridines

Synthesis and functionalization of azetidine‐containing small macrocyclic peptides

Cyclic peptides are increasingly important structures in drugs but their development can be impeded by difficulties associated with their synthesis. Here, we introduce the 3‐aminoazetidine (3‐AAz) subunit as a new turn‐inducing element for the efficient synthesis of small head‐to‐tail cyclic peptides. Greatly improved cyclizations of tetra‐, penta‐ and hexapeptides (28 examples) under standard reaction conditions are achieved by introduction of this element within the linear peptide precursor. Post‐cyclization deprotection of the amino acid side chains with strong acid is realized without degradation of the strained four‐membered azetidine. An special feature of this chemistry is that further late‐stage modification of the resultant macrocyclic peptides can be achieved via the 3‐AAz unit.  This is done by: (i) chemoselective deprotection and substitution at the azetidine nitrogen, or by (ii) a click‐based approach employing a 2‐propynyl carbamate on the azetidine nitrogen. In this way, a range of dye and biotin tagged macrocycles are readily produced. Structural insights gained by XRD analysis of a cyclic tetrapeptide indicate that the azetidine ring encourages access to the less stable, all‐trans conformation. Moreover, introduction of a 3‐AAz into a representative cyclohexapeptide improves stability towards proteases compared to the homodetic macrocycle.</p

Synthesis and functionalization of azetidine‐containing small macrocyclic peptides

Cyclic peptides are increasingly important structures in drugs but their development can be impeded by difficulties associated with their synthesis. Here, we introduce the 3‐aminoazetidine (3‐AAz) subunit as a new turn‐inducing element for the efficient synthesis of small head‐to‐tail cyclic peptides. Greatly improved cyclizations of tetra‐, penta‐ and hexapeptides (28 examples) under standard reaction conditions are achieved by introduction of this element within the linear peptide precursor. Post‐cyclization deprotection of the amino acid side chains with strong acid is realized without degradation of the strained four‐membered azetidine. An special feature of this chemistry is that further late‐stage modification of the resultant macrocyclic peptides can be achieved via the 3‐AAz unit.  This is done by: (i) chemoselective deprotection and substitution at the azetidine nitrogen, or by (ii) a click‐based approach employing a 2‐propynyl carbamate on the azetidine nitrogen. In this way, a range of dye and biotin tagged macrocycles are readily produced. Structural insights gained by XRD analysis of a cyclic tetrapeptide indicate that the azetidine ring encourages access to the less stable, all‐trans conformation. Moreover, introduction of a 3‐AAz into a representative cyclohexapeptide improves stability towards proteases compared to the homodetic macrocycle.</p