Lastly, we were able to demonstrate that this cavitandimposed shape selectivity can be translated into regioselectivity in the OAT products. For this purpose, 9 was treated with an equimolar amount of an asymmetric linear bisphosphine 13, featuring two phosphine groups of significantly differing steric bulk (PMe2 vs PCy2) at its termini. Although this time the oxidation was incomplete after 4 hr at r.t (75%), only the dimethylphosphine terminus -small enough to enter the cavity -became oxidized in the reaction (c). Such a regioselective oxidation of asymmetric bisphosphines by conventional synthetic methods is highly challenging, and is quite reminiscent of enzymatic systems, capable of performing organic transformations with high degrees of regioselectivity. 93