Stereoselective Synthesis of <i>o</i>-Bromo (or Iodo)aryl P-Chirogenic Phosphines Based on Aryne Chemistry

Abstract

The efficient synthesis of chiral or achiral tertiary phosphines bearing an <i>o</i>-bromo (or iodo)­aryl substituent is described. The key step of this synthesis is based on the reaction of a secondary phosphine borane with the 1,2-dibromo (or diiodo)­arene, owing to the formation in situ of an aryne species in the presence of <i>n</i>-butyllithium. When P-chirogenic secondary phosphine boranes were used, the corresponding <i>o</i>-halogeno-arylphosphine boranes were obtained without racemization in moderate to good yields and with ee up to 99%. The stereochemistry of the reaction, with complete retention of the configuration at the P atom, has been established by X-ray structures of P-chirogenic <i>o</i>-halogenophenyl phosphine borane complexes. The decomplexation of the borane was easily achieved without racemization using DABCO to obtain the free <i>o</i>-halogeno-arylphosphines in high yields