Formation of Phosphinite Boranes

Reaction conditions are very straightforward, consisting of stirring the aminophosphines 8 in freshly distilled methanol in the presence of 1 equivalent of sulfuric acid for several hours at 0 °C or room temperature. Methylpho-sphinite boranes 9 are either clear liquids or crystalline solids, which can be easily purified by column chromatography or recrystallisation and, in contrast to 8, are indefinitely stable in air. Another advantage is that the reaction yields one equivalent of unchanged ephedrine, which can be recycled. The reaction is 

The reaction of aminophosphine borane 21 with o-iodophenethyl alcohol yields the phosphinite borane 22, with the expected inversion of configuration, although only in 24% yield. 

Deboronation of 22 in refluxing diethylamine affords 23 in quantitative yield whereas methylphosphinites 24-26 have been reported by Muller and co-workers after borane decomplexation with morpholine at room temperature. The absolute configuration of 24 was confirmed by the X-ray structure of a derived palladium complex. 

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Oxazaphospholidine boranes 82 react regio- and stereoselectively with alkyl lithiums or aryl lithiums in THE at —78°C, with formation of acyclic phosphinite boranes 83. Various substituents R =n-alkyl, c-alkyl, aryl, or ferrocenyl were introduced into aminophosphine boranes 82 in high yield (93-97%) and with high diastereoselectivity dr >98 2). The reaction proceeded with retention of configuration at phosphorus. RecrystaUization of aminophosphine boranes 83 in propanol gave the diastereoisomerically pure products [53]. Acid methanolysis of aminophosphine boranes 83 led to the formation of phosphinite boranes 84 with inversion of configuration on the E-center to yield the compotmds 84 in high... 

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