Evaluation and Development of Methodologies for the Synthesis of Thiophosphinic Acids

Access to Enantiomerically Pure P-Stereogenic Primary Aminophosphine Sulfides under Reductive Conditions

Stereochemically pure phosphines with phosphorus-heteroatom bonds and P-centered chirality are a promising class of functional building blocks for the design of chiral ligands and organocatalysts. A route to enantiomerically pure primary aminophosphine sulfides was opened through stereospecific reductive C-N bond cleavage of phosphorus(V) precursors by lithium in liquid ammonia. The chemoselectivity of the reaction as a function of reaction time, substrate pattern, and chiral auxiliary was investigated. In the presence of exclusively aliphatic groups bound to the phosphorus atom, all competing reductive side reactions are totally prevented. The absolute configurations of all P-stereogenic compounds were determined by single-crystal X-ray diffraction analysis. Their use as synthetic building blocks was demonstrated. The lithium salt of (R)-BINOL-dithiophosphoric acid proved to be a useful stereochemical probe to determine the enantiomeric purity. Insights into the coordination mode of the lithium-based chiral complex formed in solution was provided by NMR spectroscopy and DFT calculations.

Design, synthesis, and evaluation of chiral thiophosphorus acids as organocatalysts

A series of P-stereogenic chiral phosphorus acids (CPAs) were synthesized to determine the requirements for efficient asymmetric organocatalysis. In order to eliminate the need for C₂-symmetry in common CPAs, various scaffolds containing C₁-symmetrical thiophosphorus acids were chosen. These new compounds were synthesized and evaluated in the asymmetric transfer hydrogenation of 2-phenylquinoline. Although the efficacy of the thiophosphorus acids was disappointing for this reaction, the work should be useful for developing structural design elements.

Metal-Free Regioselective Hydrophosphorodithioation of Spirovinylcyclopropyl Oxindoles: Rapid Access to Allyl Dialkylphosphorodithioates

Phosphorodithioates are important substructures due to their great use in bioactive compounds and functional materials. A metal-free 1,5-addition of spirovinylcyclopropyl oxindoles have been developed by choosing P₄S₁₀ and alcohol as nucleophiles through the regioselective ring-opening of spirovinylcyclopropyl oxindoles. This method provides access to allylic organothiophosphates with high efficiency, wide functional group tolerance, good chemo- and regioselectivity, and E-selectivity. 1,3-Addition products were also prepared in high yield. Furthermore, the resulting organothiophosphates could be readily transformed into other allylic derivatives.