Cross-metathesis functionalized exo-olefin derivatives of lactide

Poly(lactic acid) is at the forefront of research into alternative replacements to fossil fuel derived polymers, yet preparation of derivatives of this key biodegradable polymer remain challenging. This paper explores the use of two derivatives of lactide, each of which features an exocyclic olefin, andtheir pre-polymerization modification by olefin cross-metathesis. Methylenation of lactide with Tebbe’s reagent generates a novel 5-methylenated lactide monomer, (3S,6S)-3,6-dimethyl-5-methylene-1,4-dioxan-2-one, complementing the previously reported 3-methylenated (6S)-3- methylene-6-methyl-1,4-dioxan-2,5-dione. While ring-opening of each monomer is not productive, olefin cross-metathesis can be used to functionalize each of the exocyclic olefins to produce a family of monomers. The ring-opening polymerization of these new monomers, and their hydrogenatedcongeners, is facilitated by organo- and Lewis-acid catalysts. Together, they offer a new strategy for derivatising and altering the properties of poly(lactic acid).