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

Abstract

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.

Impact of regiochemistry in energetic materials science: a case of (nitratomethyl-1,2,3-triazolyl)furazans

“…It is interesting to note that regioisomers 4a and 4b possess rather different physical properties: the melting point and decomposition temperature of 4a are 74 °C and 137 °C, respectively, while 4b is liquid under ambient conditions and exhibits a higher decomposition onset at 167 °C. This feature is in line with previous findings on the substantially different physicochemical properties of energetic nitrato-functionalized cyclobutane 30 and azetidine 31 regioisomers, as well as a series of regioisomeric nitro-1,2,3-triazoles. 50 All the synthesized energetic materials 4a–c have high combined nitrogen–oxygen contents (76–77%) and good experimental densities (1.43–1.49 g cm −3 for liquid samples 4b and 4c and 1.72 g cm −3 for solid 4a ).…”

“…In this regard, very recent studies challenged the previous assumption that regiochemistry does not influence the properties and performance of energetic materials. [30][31][32][33] Indeed, the calculated energetic parameters (oxygen balance, detonation velocity and pressure) of regioisomers are similar, while their physical properties (aggregation state, thermal and mechanical stabilities) differ significantly. Since several types of regioisomeric 5-membered nitrogen heterocycles (e.g., 1,2,3-triazole) are easily synthesized via 1,3-dipolar cycloaddition, we decided to use this approach to study the influence of regioisomerism on the properties of energetic materials.…”

Mechanisms and Synthetic Strategies in Visible Light‐Driven [2+2]‐Heterocycloadditions

“…The authors explained the kinetically preferred formation of the exo ‐isomer as a result of the minimized steric interactions of the alkene substituent with the isoxazolidine ring in intermediate 88 (Figure 18). Interestingly, this process has been recently applied to the preparation of azetidine‐based energetic materials [64] …”

Mechanisms and Synthetic Strategies in Visible Light‐Driven [2+2]‐Heterocycloadditions

“… List of energy transfer catalysts used in [2+2]‐heterocycloadditions (values of E T obtained from Refs. [64–66]). …”