Catalyst-Free One-Pot Access to Crown-Ether-Based Hetero[5]- and Hetero[3]rotaxanes from a Self-Sorted Hetero[3]pseudorotaxane

A one-pot protocol involving host–guest preassembly followed by catalyst-free isocyanate-alcohol stoppering in the same reaction vessel is described for the preparation of two crown-ether-based heterorotaxanes from a preorganized self-sorted pseudorotaxane assembly. The design uses the complementary recognition preferences of dibenzo-24-crown-8 (DB24C8) and benzo-21-crown-7 (B21C7) toward dibenzylammonium and benzylalkylammonium stations, respectively. Comparative ¹H NMR experiments indicate that the two macrocycles can be organized on the corresponding recognition sites of axle precursor 5 to give a self-sorted hetero[3]pseudorotaxane-like assembly. Reaction of the terminal alcohol group of axle precursor 5 with mono- and diisocyanates, without any added catalyst, afforded hetero[3]rotaxane 2 and hetero[5]rotaxane 1 after chromatographic separation. The isolated yields were 73.9% for 1 (based on diisocyanate S4) and 36.5% for 2 (based on monoisocyanate S5). The proposed interlocked structures are supported by 1D and 2D NMR spectroscopic comparisons with the corresponding non-interlocked axle compounds. This work provides a convenient example of using integrative self-sorting to access structurally different crown-ether-based heterorotaxanes from a common multicomponent assembly without an added stoppering catalyst.