Novel concepts in directed biaryl synthesis, XXXVII. Synthesis and enantiomerization of a nonracemic 2-hydroxy-2′-biarylcarbaldehyde, a probable intermediate in the atropo-enantioselective ring opening of biaryl lactones

Abstract

The directed preparation of a “free”, i.e. nonprotected biaryl with a phenolic OH function and a formyl group in opposite ortho positions, in a nonracemic form, is described. The free activation barrier ΔG≠ for the atropisomerization, which was determined to be 99.2 kJ mol−1, is far lower than expected for an exclusively physical rotation process and is more likely in agreement with an isomerization via lactol-type cyclic intermediates previously postulated.