Synthesis of Simple 3,3-Diarylazetidines from N-Boc-3-arylazetidinols Using Friedel-Crafts Arylation Conditions

Rapid access to azetidines via allylation of azabicyclo[1.1.0]butanes by dual copper/photoredox catalysis

Recently, the strain-release-driven synthesis of N1/C3 functionalized azetidines from azabicyclo[1.1.0]butanes has generated significant interest in the fields of medicinal and synthetic chemistry. This paper presents a mild and efficient dual copper/photoredox-catalyzed multi-component allylation of azabicyclo[1.1.0]butanes using a radical-relay strategy. This strategy enables the synthesis of C3 quaternary center-containing azetidines via a radical relay mechanism with a high yield of 91%. The method's utility is highlighted by late-stage derivatization of bioactive molecules, demonstrating exceptional functional group compatibility.

Modular Synthesis of 3,3-Disubstituted Azetidines via Azetidinylation Reagents

Azetidines represent an attractive and emerging design option in medicinal chemistry owing to their small size and polar nature, as well as their potential to significantly impact the physicochemical properties of drug molecules. However, traditional methods for the synthesis of 3,3-disubstituted azetidines usually require higher step counts or exhibit poor functional group compatibility. Herein, we report a modular synthesis strategy for 3,3-disubstituted azetidines based on azetidinylation reagents. The practicality of this method is further exemplified by the use of readily available starting materials, mild reaction conditions, and a very broad substrate scope.

Azetidines with All-Carbon Quaternary Centers: Merging Relay Catalysis with Strain Release Functionalization

Given the importance and beneficial characteristics of decorated azetidines in medicinal chemistry, efficient strategies for their synthesis are highly sought after. Herein, we report a facile synthesis of the elusive all-carbon quaternary-center-bearing azetidines. By adopting a well-orchestrated polar-radical relay strategy, ring strain release of bench-stable benzoylated 1-azabicyclo[1.1.0]butane (ABB) can be harnessed for nickel-catalyzed Suzuki Csp2-Csp3 cross-coupling with commercially available boronic acids in broad scope (>50 examples), excellent functional group tolerance, and gram-scale utility. Preliminary mechanistic studies provided insights into the underlying mechanism, wherein the ring opening of ABB with a catalytic quantity of bromide accounts for the conversion of ABB into a redox-active azetidine, which subsequently engages in the cross-coupling reaction through a radical pathway. The synergistic bromide and nickel catalysis could intriguingly be derived from a single nickel source (NiBr2). Application of the method to modify natural products, biologically relevant molecules, and pharmaceuticals has been successfully achieved as well as the synthesis of melanocortin-1 receptor (MC-1R) agonist and vesicular acetylcholine transporter (VAChT) inhibitor analogues through bioisosteric replacements of piperidine with azetidine moieties, highlighting the potential of the method in drug optimization studies. Aside from the synthesis of azetidines, we demonstrate the ancillary utility of our nickel catalytic system toward the restricted Suzuki cross-coupling of tertiary alkyl bromides with aryl boronic acids to construct all-carbon quaternary centers.

Deconstructive isomerization of azetidinols via C-C bond cleavage enabled by N-heterocyclic carbene (NHC) catalysis

Herein, we describe an N-heterocyclic carbene (NHC)-catalyzed deconstructive isomerization of azetidinols via an inert C-C bond cleavage. It provides a direct and supplementary pathway to access α-amino ketone and oxazol-2-one derivatives in moderate to good yields. DFT calculation supports the proposed mechanism in which NHC undergoes a concerted proton transfer and ring-opening process. This reaction features non-metal catalysis, simple reaction operation, excellent regioselectivity and gram-scale synthesis.