Conformational studies of biaryl-bridged seven-membered lactones with a quaternary carbon center.

We show the synthesis and conformational studies of a series of 7,7-disubstituted-dibenzo[,]oxepin-6(7)-ones that feature biaryl-bridged seven-membered lactones with a quaternary carbon center, in which the larger substituents prefer the axial positions. Further studies on the crystal structures and DFT calculations revealed that the high selectivity observed is attributed to the volume of substituents.