Moderation of the Electronic Structure of Phosphamides to Execute the Catalytic Appel Reaction Bypassing Phosphine

A set of structurally analogous, albeit electronically distinct, phosphamides (1aa-10aa) is prepared, and the effect of the electronic amendment due to p-substitution has been tested for the conversion of alcohols to halides via the Appel reaction. The -OMe-substituted diphosphamide (8aa) remains the most active, providing ∼96% conversion of alcohols to halides with a TON of 11 in moderate reaction conditions with a large substrate scope. Halide formation follows a pseudo-first-order rate with a constant rate (kobs) of 7.13 × 10-5 s-1. Temp-dependent kinetics and Eyring analyses reveal the activation parameters ΔH‡ of 28.95 (±1.6) kcal mol-1, ΔS‡ of -70.02 (±0.4) cal K-1 mol-1, and ΔG‡298 of 49.81 (±1.2) kcal mol-1. The deuterium labeling study highlights the O-H dissociation of the alcohol as the rate-determining step, while the Hammett analysis with p-substituted benzyl alcohols indicates a positive charge accumulation at the phosphorus center during the Appel reaction. The HOMO-LUMO energy and NPA analyses show that p-OMe substitutions in 8aa make the "P═O" bond more ionic and corresponding aminophosphine is nucleophilic, which are favorable for the Appel reaction. In situ detection of the Appel salt, [R3PX]CX3 and alkoxy phosphonium cation [R3POR]X, validates the reaction pathway mediated by the phosphamides.

A simple and efficient synthesis of 9-arylfluorenes via metal-free reductive coupling of arylboronic acids and N-tosylhydrazones in situ

A general, yet efficient synthesis method of 9-arylfluorenes via metal-free reductive coupling of N-tosylhydrazones and arylboronic acids has been developed.

TfOH catalyzed synthesis of 9-arylfluorenes via tandem reaction under warm and efficient conditions

A tandem ring-closing reaction was developed for the synthesis of 9-arylfluorenes and their derivatives. The reaction is metal-free, straightforward and efficient under warm conditions and more than 99% yield is obtained.