The dynamic resolution of tertiary phosphines and phosphine oxides was monitored by NMR spectroscopy. It was found that the stereoselectivity in this process is set during the formation of the diastereomeric alkoxyphosphonium salt (DAPS), since the initial de of this species limits the final ee of both phosphine oxides and phosphine boranes. Spontaneous thermal decomposition of DAPSmonitored by 31P-NMR shows that diastereomeric self-enrichment of the remaining DAPS is typically observed indicating higher decomposition rate constant for the minor diastereomer of the DAPS. This crucial observation was confirmed by reductive trapping of the unreacted enriched DAPS with L-Selectride at different time intervals after the start of reaction, which gives progressively higher ee of phosphine borane product with time. Thus, slower formation and faster subsequent collapse of minor DAPS isomer are associated with double kinetic resolutionprocess furnishing up to 97% ee material. Figure 1. <img src='https://acs-archive-assets2.s3.amazonaws.com/241nm/uploads/71405_abstractacs.jpg' alt='' />

Thermodynamically interconnected sequential kinetic resolution through a common intermediate leading to chiral phosphine with surplus enantioselectivity

248th National Meeting (2014)

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