The selectivity in the arylation of 16a is noteworthy in that the monoarylated product 18a is formed almost exclusively as the trans isomer, whereas the diarylated product 17a is formed exclusively as the all cis isomer. This can be rationalised (Scheme 7) by assuming that the directing group can more effectively mediate the C-H activation step when it occupies an axial position, giving cis selectivity. Thus, arylation cis to the directing group gives a disubstituted cyclohexane cis-18a with one substituent is axial and one equatorial. This effectively lowers the energy of the conformation in which the directing group is axial, promoting a second C-H insertion reaction. In contrast, the formation of trans-18a presumably involves some distortion of the chair in the intermediate Pd complex trans-23.