Photochemical Strategies Enable the Synthesis of Tunable Azetidine-Based Energetic Materials.

Despite their favorable properties, azetidines are often overlooked as lead compounds across multiple industries. This is often attributed to the challenging synthesis of densely functionalized azetidines in an efficient manner. In this work, we report the scalable synthesis and characterization of seven azetidines with varying regio- and stereochemistry and their application as novel azetidine-based energetic materials, enabled by the visible-light-mediated aza Paternò-Büchi reaction. The performance and stark differences in the physical properties of these new compounds make them excellent potential candidates as novel solid melt-castable explosive materials, as well as potential liquid propellant plasticizers. This work highlights the scalability and utility of the visible-light aza Paternò-Büchi reaction and demonstrates the impact of stereochemical considerations on the physical properties of azetidine-based energetics. Considering the versatility and efficiency of the presented synthetic strategies, we expect that this work will guide the development of new azetidine-based materials in the energetics space as well as other industries.

Visible-Light-Enabled Paternò-Büchi Reaction via Triplet Energy Transfer for the Synthesis of Oxetanes.

One of the most efficient ways to synthesize oxetanes is the light-enabled [2 + 2] cycloaddition reaction of carbonyls and alkenes, referred to as the Paternò-Büchi reaction. The reaction conditions for this transformation typically require the use of high energy UV light to excite the carbonyl, limiting the applications, safety, and scalability. We herein report the development of a visible-light-mediated Paternò-Büchi reaction protocol that relies on triplet energy transfer from an iridium-based photocatalyst to the carbonyl substrates. This mode of activation is demonstrated for a variety of aryl glyoxylates and negates the need for both visible-light-absorbing carbonyl starting materials and UV light to enable access to a variety of functionalized oxetanes in up to 99% yield.

Tetrahydropyridines via FeCl3-Catalyzed Carbonyl-Olefin Metathesis.

Herein we describe the application of Lewis-acid-catalyzed carbonyl-olefin metathesis toward the synthesis of substituted tetrahydropyridines from commercially available amino acids as chiral pool reagents. This strategy relies on FeCl3 as an inexpensive and environmentally benign catalyst and enables access to a variety of substituted tetrahydropyridines under mild reaction conditions. The reaction proceeds with complete stereoretention and is viable for a variety of natural and unnatural amino acids to provide the corresponding tetrahydropyridines in up to 99% yield.

Generation of a glycosylated asparagine residue through chemoselective acylation of a glycosylhydrazide.

Herein, we report the first selective anomeric N-acylation of a glycosylhydrazide. We show that this transformation can be harnessed to generate amino acid building blocks including FmocAsn(GlcNAc)OH (1), a residue that has been previously shown to be a competent reagent in the solid-phase peptide synthesis of N-linked glycopeptides.