摘要：

Diarylated cyclooctenes encode head-to-head styrene dyads that form precision polyolefns after ring-opening metathesis polymerization and hydrogenation.The'on demand'synthesis of sequence-controlled synthetic polymers is a notable goal in organic chemistry1.Programming the primary structure within polyolefin copolymer backbones is challenging owing to limitations associated with inherent reactivity ratios of common monomers,such as ethylene and styrene,in traditional polymerization methods2.Whereas post-polymerization programming through direct functionalization of polyenes can provide access to such scaffolds,they are often poorly soluble and methods that enable exhaustive func-tionalization with stereodefinition are lacking.Given the importance of relative stereochemistry,sequence,and spacing between pendant chains for bulk materials properties,new methods that access precisely sequenced polymers remain highly sought after.Now,writing in Nature Synthesis,Engle,Gutekunst,Liu and co-workers report the synthesis of precision polyolefins possessing head-to-head styrene dyads that exhibit relative syndiotactic character3.Key to their strategy is the use of 1,5-cyclooctadiene(1,5-COD)in a nickel-catalysed alkene diarylation reaction,wherein the inherent transannular directing ability of the spectator alkene controls the iteroselectivity of the reaction,affording syn-1,2-diarylated products.Computational analysis reveals the role of the boronate species in promoting the migratory insertion step,which in turn controls the enantioselectivity.The resultant 5,6-diarylcyclooctenes-encoded with a butadiene-styrene-styrene sequence-are suitable for ring-opening metathesis polymerization(ROMP),leading to polymers with glass transition temperatures ranging from 54-108 ℃ that map onto the styrene-ethylene copolymer backbone after hydro-genation.Whilst alkene diarylation has been known for almost 40 years(ref.4)-with efforts in the past decade enhancing the scope of products accessed through nickel catalysis5-7-the integration of this potent strategy to attain precisely sequenced polymers is underexplored8.In this study,alkene dicarbofunctionalization,followed by subsequent ROMP and hydrogenation,is leveraged as a potent strategy to access polymers that,de facto,correspond to those attained from the hypothetical exhaustive arylation of polyenes(Fig.1a).

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