Racemization in suzuki couplings: a quantitative study using 4-hydroxyphenylglycine and tyrosine derivatives as probe molecules.

ABSTRACT

Reaction conditions considered to be typical in Suzuki couplings can cause significant (up to 34% of the unwanted enantiomer) loss of optical purity in sensitive substrates such as hydroxyphenylglycine 1. This may be remedied using sodium succinate instead of sodium carbonate as base, but chemical yields are somewhat lower. Optically pure biaryl amino acids related to those found in the chloropeptins and vancomycin were synthesized by Suzuki coupling of 1 with indolylboronic acids 6-8 and with cyclic boronic acid 9.