Synthesis and reactions of optically pure cyclohexyl(<i>o</i>‐methoxyphenyl)phosphine‐borane and <i>t</i>‐butyl‐(<i>o</i>‐methoxyphenyl)phosphine‐borane

Abstract

Abstract Cyclohexyl(o‐methoxyphenyl)menthyloxyphosphineborane and t‐butyl(o‐methoxyphenyl)menthyloxyphosphine‐borane were prepared from dichlorocyclohexylphosphine and t‐butyldichlorophosphine by successive treatments with (−)‐menthol, o‐methoxyphenylmagnesium bromide, and borane‐THF complex. The separated pure diastereomers of each of the compounds underwent reaction with lithium naphthalenide to afford optically pure cyclohexyl(o‐methoxyphenyl)phosphine‐borane and t‐butyl(o‐methoxyphenyl)phosphine‐borane, respectively. These secondary phosphine‐boranes reacted readily with various electrophiles in the presence of bases with virtually net retention of configuration. A new chiral phosphine ligand, (S,S)‐1,2‐bis[cyclohexyl(o‐methoxyphenyl)phosphino]ethane was synthesized via the optically pure phosphine‐boranes.