Selective Alkene Functionalization as a Platform for Energetic Materials Development
Abstract
The development of new energetic materials with tunable physical and chemical properties hinges upon the discovery and development of selective, robust, and scalable methods for their preparation. Existing synthetic approaches, however, are limited in several key respects. First, certain integral transformations employ corrosive reagents, require harsh reaction conditions, and generate significant quantities of waste. Second, many promising energetics remain inaccessible on sufficient scale, which limits their practical use. Third, at the discovery stage, certain key structureactivity relationships remain difficult to probe, such as the influence of stereochemistry on properties. This proposal seeks to bridge these gaps through the invention of new catalytic methods to install explosophores (functional groups that gives the molecule its explosive properties) onto commonly encountered starting materials, namely alkenes and their derivatives. In our proposed studies, we will develop Wacker- and Heck-type alkene addition processes capable introducing nitro-containing nucleophiles and electrophiles in a modular fashion with mechanism-based stereoselectivity control (anti and syn, respectively). In this way, we will significantly expand synthetic access to densely functionalized carbogenic core structures bearing explosophores. To complement this approach, we will also pursue complementary synthetic strategies that employ alkene-derived reaction partners. Taking inspiration from emerging metal-catalyzed C(alkyl)-C(alkyl) and C(alkyl)-heteroatom cross-coupling methods, we will design catalytic protocols for engaging nitrite as a nucleophilic nitro source in cross coupling with alkylmetal and alkyl(pseudo)halide coupling partners. Finally, strategic application of these new methods with strained alkene starting material will allow for streamlined access to high-energy materials with unprecedented levels of selectivity control. By taking advantage of innate functional groups to direct or block the metal from engaging one of the two potential reactive faces of the alkene, we hypothesize that all possible cis/trans stereoisomers can be accessed. Once these techniques are validated with model systems, we will apply them to facilitate synthesis of validated energetics as well as novel candidate compounds. The properties of new energetics will be measured, and detailed structureactivity relationships will be developed to facilitate iterative molecular design. We anticipate that the proposed studies in synthetic chemistry will have significant impact in basic and applied sciences. Major expected outcomes in terms of preparative capabilities include: (1) the development of a new toolkit of catalytic reactions for stereoselective addition of nitro-containing fragments to alkenes; (2) discovery of cross-coupling-type methods for accessing nitroalkanes; (3) refined mechanistic understanding of NO2 nucleophiles and electrophiles in catalytic couplings relevant to process development. Major expected energetics outcomes include: (1) preparation of previously unknown strained carbocycles adorned with explosophores; (2) detailed structureactivity relationships, particularly with respect to explosophore stereochemistry; (3) modular discovery platforms for interactive molecular design. Collectively, these findings will expand DoD capabilities in energetics discovery and development, with wide-ranging impact in national defense. This proposal is entitled Selective Alkene Functionalization as a Platform for Energetic Materials Development.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 20, 2020
- Source ID
- N000142012606
Entities
People
- Keary M Engle
Organizations
- Office of Naval Research
- Scripps Research
- United States Navy