Stereoselective, Oxidative One-Carbon Degradation of Alkyl(dimethyl)phosphine-Boranes. Synthesis of Enantiomerically Enriched Secondary Phosphine-Boranes

Unsymmetrical P-Chirogenic Bis(phosphane) Ligands: Their Preparation and Use in Rhodium-Catalyzed Asymmetric Hydrogenation

“…Reduction of these carboxylic acids by boraneϪTHF afforded quantitative yields of the (R P )-alcohols 4aϪi, which were treated with TsCl or MsCl to give the corresponding (R P )-cofigured tosylates 5aϪd or mesylates 6aϪg, respectively. These compounds were then coupled with lithiated (S P )-alkyl(methyl)phosphaneϪborane adducts [21] to provide the unsymmetrical (S P ,S PЈ )-BisP*ϪBH 3 adducts 7aϪk (97% ee) together with small amounts of the corresponding diastereoisomers. These phosphaneϪboranes 3Ϫ7 were also very stable in air.…”

Improved synthetic routes to methylene-bridged P-chiral diphosphine ligands via secondary phosphine–boranes

“…11 We found also that compound (R)-2 was subjected to stereospecific, oxidative onecarbon degradation on treatment with K 2 S 2 O 8 in the presence of RuCl 3 as a catalyst to afford secondary phosphine-borane (S)-3 in high yield. 11 It was also observed that the phosphido anions derived from chiral secondary phosphine-boranes exhibited strong nucleophilicity during substitution reaction with alkyl halides while keeping the stereochemical integrity at the P-stereogenic center. 12 Based on these facts, we envisioned that the reaction of compound (S)-3 with a sulfonate derivative of compound (R)-2 would yield the precursor of (R,R)-t-Bu-MiniPHOS (Scheme 2).…”

Asymmetric Deprotonation with Alkyllithium–(−)‐Sparteine

“…Applying dihalides, essentially enantiomerically pure diphosphines such as 206, besides few of the meso-diastereomer, were obtained. Borane is removed by treatment with diethylamine to yield the free tertiary phosphines 207. enantiomerically enriched lithium phosphides of type 204 were also prepared by oxidation of the lithium compounds 196 and oxidative degradation of the hydroxymethyl group 154 or reductive cleavage of the benzophenone adducts 155 .…”