In Situ Phosphine Oxide Reduction: A Catalytic Appel Reaction

Abstract

Several important reactions in organic chemistry thrive on stoichiometric formation of phosphine oxides from phosphines. To avoid the resulting burden of waste and purification, cyclic phosphine oxides were evaluated for new catalytic reactions based on in situ regeneration. First, the ease of silane-mediated reduction of a range of cyclic phosphine oxides was explored. In addition, the compatibility of silanes with electrophilic halogen donors was determined for application in a catalytic Appel reaction based on in situ reduction of dibenzophosphole oxide. Under optimized conditions, alcohols were effectively converted to bromides or chlorides, thereby showing the relevance of new catalyst development and paving the way for broader application of organophosphorus catalysis by in situ reduction protocols.

A convenient and mild chromatography-free method for the purification of the products of Wittig and Appel reactions

“…Two protocols for carrying out Appel reactions that are catalytic in phosphine oxide have been reported recently. 21,22,23 In the process of Denton and co-workers, oxalyl chloride reacts with the oxide to give chlorophosphonium 90 salt (vide infra), which in turn reacts with alcohol to give alkoxyphosphonium salt, resulting in alkyl chloride and regenerating phosphine oxide. Denton et.…”

Investigation of the Appel reaction with bromotrichloromethane-triphenylphosphine (CBrCl3/PPh3)

“…1 H NMR (at 400 MHz) and 13 C NMR (at 100.5 MHz) spectra were taken on a Varian 400 MHz spectrometer. IR measurements were performed on a Thermo Nicolet FT-IR spectrometer, model Nexus 470.…”

“…Also, steroidal alcohols cholesterol (11) and sitosterol (13) have been submitted to PPh3-BrCCl3 in CH2Cl2 to again show mixtures of steroidal chlorides and bromides (Table 2). Aliquots were drawn from the selected reaction mixtures.…”

Cyclic Phosphine Oxides and Phosphinamides from Di-Grignard Reagents and Phosphonic Dichlorides: Modular Access to Annulated Phospholanes

“…NMR data was in good agreement with that previously reported. 8 (racemic)- = 8.4 Hz,1H),1H),7.63 (dd,J = 12.3,7.3 Hz,2H),6H),1H),1H) 6, 126.1, 125.1 (d, J = 4.8 Hz), 123.8 (d, J = 12.7 Hz), 28.6 (d, J = 4.6 Hz), 27.9 (d, J = 71.4 Hz);IR (neat) v 2360IR (neat) v , 1201IR (neat) v , 1186IR (neat) v , 1111 (racemic)- 3,3a,4,7, …”