γ‐Acyloxy‐ε‐Caprolactones: Synthesis, Ring‐Opening Polymerization vs. Rearrangement by Means of Chemical and Enzymatic Catalysis

• Published in: Macromolecular Symposia
• Main Authors: Vaida, Cristian, Takwa, Mohamad, Martinelle, Mats, Hult, Karl, Keul, Helmut, Möller, Martin
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2008
• Subjects: Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1002/masy.200851203; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fmasy.200851203; https://onlinelibrary.wiley.com/doi/pdf/10.1002/masy.200851203

Abstract Summary: γ ‐Acyloxy‐ ε ‐caprolactones ( 3a–d ) were prepared in two steps starting from 4‐hydroxy‐cyclohexanone ( 1 ). In the first step acylation of the hydroxyl group occurs and in the second step ring enlargement by Baeyer‐Villiger oxidation. If this order of reaction is inverted rearrangement occurs in the Baeyer‐Villiger oxidation of 4‐hydroxy‐cyclohexanone leading to γ ‐hydroxyethyl‐ γ ‐butyrolactone. Using the first procedure γ ‐acetyloxy‐ ( 3a ), γ ‐benzoyloxy‐ ( 3b ), γ ‐acryloyloxy‐ ( 3c ), and γ ‐ methacryloyloxy‐ ε ‐caprolactone ( 3d ) were prepared. These monomers and for comparison reasons ε ‐caprolactone and γ ‐methyl‐ ε ‐caprolactone were polymerized by means of chemical and enzymatic catalysis. The results were different depending on the monomer structure and catalyst used. In the presence of a chemical catalyst, all the monomers, except γ ‐acetyloxy‐ ε ‐caprolactone, undergo controlled ring‐opening polymerization. γ ‐Acetyloxy‐ ε ‐caprolactone ( 3a ), however, rearranges to a large extent under polymerization conditions to give γ ‐acetyloxyethyl‐ γ ‐butyrolactone ( 6a ). In the presence of an enzyme (Novozyme 435, Lipase B from Candida antarctica (CALB) immobilized on a macroporous resin) all γ ‐acyloxy‐ ε ‐caprolactones partly rearrange to result the corresponding γ‐ acyloxy‐ γ ‐butyrolactones, while ε ‐caprolactone and γ ‐methyl‐ ε ‐caprolactone yield the corresponding polymers, the latter even in a stereoselective manner as reported earlier in the literature. A molecular dynamic study was performed with 3a and 3b as substrates to gain information on the substrate recognition displayed by CALB. A mechanism for the chemically and enzymatically catalyzed reactions of γ ‐acyloxy‐ ε ‐caprolactones is proposed.