Reduction of Tertiary Phosphine Oxides by BH3 Assisted by Neighboring­ Activating Groups

Abstract

Tertiary sulfanylphosphine and aminoalkylphosphine oxides can be easily converted into the corresponding tertiary sulfanylphosphine- and aminoalkylphosphine-boranes, respectively, through the facile P=O bond reduction by borane complexes. The easy reduction of the strong P=O bond by BH3, a mild reducing agent, has been achieved through an intramolecular P=O -- B complexation directed by proximal SH or NH activating groups located at the α- or β-position to the P=O bond. A generalized reduction mechanism has been proposed.

Flexible Synthesis of Phosphoryl-Substituted Imidazolines, Tetrahydropyrimidines, and Thioamides by Sulfur-Mediated Processes

“…All reactions were carried out using freshly distilled and dry solvents. Phosphinic chlorides are readily available from chloromethylphosphonic dichloride by simple treatment with amines, alcohols, and Grignard reagents. − …”

“…1 Chloromethylphosphonic Acid N-Methyl-N-phenyl Azepaneamide (1g). The compound was obtained according to a literature protocol, 24 as white solid. Mp: 97−99 °C.…”

Myrtenal and Myrtanal as Auxiliaries in the Synthesis of Some C,P-Stereogenic Hydroxyphosphine Oxides and Hydroxyphosphine-Boranes Possessing up to Four Contiguous Centers of Chirality

“…One of the important features of α-hydroxyphosphine oxides is their ability to undergo very facile reduction upon treatment with BH 3 at room temperature, to give directly the corresponding borane-protected α-hydroxyphosphines with clean inversion of configuration at the P-centre [26][27][28][29]. To further explore this possibility, two of the synthesized P,C-stereogenic α-hydroxyphosphine oxides, i.e., (R P )-7a-I, and (S P )-9c-II were subjected to such reductions under the previously reported conditions [26].…”

Knoevenagel Condensation of Phosphinoylacetic Acids with Aldehydes: An Efficient One-Pot Strategy for the Synthesis of P-Functionalized Alkenyl Compounds

“…According to the general procedure, the reaction of 2a (198 mg, 0.76 mmol) afforded product 4a as a white solid; yield: 144 mg (83%); mp 116-117 °C (Lit. 26…”