Synthesis and Reactivity of a P-Hydrogen Functionalized Benzazaphosphole

Abstract

P–H functionalized benzazaphosphole 3 was synthesized via reduction of chlorophosphine 2 with LiAlH4. Its weak hydridic character was demonstrated via insertion into electrophilic trifluoroacetophenone and dehydrocoupling with fluorinated alcohols. However, 3 readily inserted with difluorocarbene affording 5, which was fully characterized by multinuclear NMR spectroscopy, HRMS, elemental analysis, and X-ray crystallography. The diastereotopic fluorines of the –CF2H group displayed a complex second-order splitting pattern in the 19F NMR spectrum and was successfully simulated using MestReNova. In addition, hydrophosphination between 3 and phenylacetylene generated a mixture of anti- and Markovnikov products 6-6ʺ. Computational modeling of the reaction revealed the anti-Markovnikov E-isomer formed via highly strained phosphirene intermediate, but the major product that crystallized out of solution was the Z-isomer, which was fully characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography.