1,3-Dipolar cycloaddition reactions of triflatophosphanes to afford functionalized azaphospholium salts and azaphospholes

Abstract

The advent of 1,3-dipolar cycloadditions in organic chemistry has introduced a powerful tool for constructing novel ring systems. However, methods for synthesizing inorganic, phosphorus-containing rings via 1,3-dipolar cycloadditions have remained scarce and are largely limited to the functionalization of phosphaalkynes. In this contribution, we describe the synthesis of 1,3-dipolar triflatophosphanes, demonstrating their ability to engage in (3 + 2)-cycloadditions with a variety of dipolarophiles. In addition to nitriles, (thio)-cyanates, iso-(thio)-cyanates, and (thio)-ketones, phosphaalkenes also exhibit reactivity, yielding a wide range of heteroatom-functionalized di- and triazaphospholium compounds. Density Functional Theory (DFT) calculations provide insight into the likely stepwise mechanism. Furthermore, the reduction of synthesized diazaphospholium salts affords neutral diazaphospholes, offering a novel route to this class of compounds. Importantly, we explored the photophysical properties of selected diazaphospholes that exhibit strong fluorescence with photoluminescence quantum yields of up to 37%, making them attractive candidates for applications in optoelectronics.