Ring-opening metathesis polymerization was used to generate an ABC triblock copolymer, containing complementary diamidopyridine (DAP) and thymine (THY) outer blocks, which assembles into spherical aggregates held together by DAP-THY noncovalent interactions. Addition of THY-containing small guest molecules results in complete opening and deaggregation of the block copolymer micelle. This molecular recognition and macroscopic response shows high selectivity to the guest structure, and tolerates only a small amount of conformational mobility in the THY guest. On the other hand, addition of a small DAP-containing guest does not break the aggregates, but instead, results in new micelles which show a different selectivity profile from the parent morphology. We have examined the effect of a number of structural features in the block copolymers, on both the extent and selectivity of their macroscopic response to guests (that is, opening of the micelle). This study has resulted in a set of structural guidelines, which help in the design of effective molecule-responsive micelles for applications in selective drug delivery, sensing, and surface patterning.

Radical reductions of halogenated precursors bearing a heterocycle exo (α) to the carbon-centered radical proceed with enhanced anti-selectivity, a phenomenon that we termed "exocyclic effect". New experimental data and DFT calculations at the BHandHLYP/TZVP level demonstrate that the origin of the exocyclic effect is linked to the strain energy required for a radical intermediate to reach its reactive conformation at the transition state (ΔE(≠)(strain)). Furthermore, radical reductions of constrained THP systems indicate that high 2,3-anti inductions are reached only when the radical chain occupies an equatorial orientation. Hydride deliveries to different acyclic substrates and calculations also suggest that the higher anti-selectivities obtained with borinate intermediates are not related to the formation of a complex mimicking an exocycle. From a broader standpoint, this study reveals important conformational factors for reactions taking place at a center vicinal to a heterocycle or an α-alkoxy group.

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The structure-activity study of a bioactive natural product containing polypropionate subunits requires that its stereoisomers also be evaluated. Therefore, a general approach to synthesize these motifs is necessary. We describe herein the synthesis of the C1-C13 polypropionate subunit of zincophorin and isomers thereof using a two-reaction sequence: an aldol reaction using a mixture of tetrasubstituted enoxysilanes and a hydrogen-transfer reaction, both under Lewis acid control. Selection of the appropriate Lewis acid dictates the stereochemical outcome of these reactions. From a tactical standpoint, this study shows how a polypropionate sequence can be read and constructed in two directions, either the east-west or the west-east approaches. The choice of the optimal route is influenced by the number of complexation sites that can interfere in the aldol step under bidentate Lewis acid control.