Templated Ring-Opening Metathesis (TROM) of Cyclic Olefins Tethered to Unimolecular Oligo(thiophene)s

We developed a fully abiotic approach to template the synthesis of discrete unimolecular polyolefins. Discrete, unimolecular oligo(thiophene)s with alternating sequence were obtained by iterative convergent/divergent couplings and then functionalized with pendant cyclic olefin monomers in the side chains. Upon treatment with the Grubbs third-generation catalyst in dilute solution (0.15 mM in DCM at 0 degrees C), the pendant monomers undergo templated ring-opening metathesis (TROM). Then, the daughter olefin is liberated from the parent thiophene by hydrolysis. Cyclooctenes undergo TROM to afford macrocyclic products that exactly replicate the chain length of the parent oligomer, as evidenced by MALDI MS/MS and NMR. Norbornene derivatives also undergo TROM and replicate unimolecular chain lengths, but in contrast, they exclusively form the linear oligomeric products with styrenic end groups. A template that was functionalized with one norbornene unit at the a chain end, followed by five cyclooctene units along the template, underwent TROM to afford the macrocyclic daughter olefin. Intertemplate metathesis is suppressed by tuning the concentration and reaction time. Using this strategy, we can effectively replicate the unimolecular nature of a template, made by labor-intensive iterative synthesis, to produce a discrete daughter oligomer by chain growth. We also demonstrate that the templates are recyclable upon hydrolytic cleavage of daughter oligomer, attachment of fresh daughter monomer, and repetition of the TROM process.