Expanding the structural diversity of discrete polymers accessible through iterative exponential growth

Abstract

Iterative exponential growth is a powerful method for the synthesis of atomically defined macromolecules. However, preparation of enantiopure IEG-ready monomers can be challenging, which may limit the attractiveness of IEG as a tool for the study of structurerelationship properties in discrete macromolecules, both in materials and in biological systems. Here, we present a new strategy for the synthesis of orthogonally protected monomers, suitable for IEG through cycles of azidation, alkyne deprotection, and CuAAC, in fewer steps and from readily available and affordable building blocks. This monomer synthesis was achieved through the development of a novel allylation methodology. Using alkynylation of epichlorohydrin, LiBr Finkelstein, and TfOH-promoted allylation, we have been able to prepare a monomer for 3A (number of carbons in each polymer repeat unit, excluding alkyne) IEG in just three steps. Furthermore, the same reactions can be integrated in the synthesis of other IEG architectures (2A/4A/5A), thus expanding the structural diversity and readily accessible substrate scope for atomically defined macromolecules. The configurations of stereogenic centers in IEG-mer backbones are defined by the starting material (R or S epichlorohydrin) and can be further controlled by combining different stereoisomers in desired fashion. This work outlines a conceptual strategy to diversify and expand the chemical space of discrete macromolecules and enable efficient and quick access to a variety of IEG-mer scaffolds.