Graphical Fatty acids slim down : A new method for γ-lactone preparation based on ring contraction has been developed. Starting from macrolides, W(OTf) 6 was used to catalyze ring-opening polymerization then depolymerization to produce the stable five-membered γ-lactones in the ionic liquid [EMIM]OTf. γ-Lactones were also produced when the substrate was extended to terminal hydroxyfatty acids. γ-Lactones are an important class of fine chemical products and are widely used in perfumes, medicines, pesticides, dyes, and other fields. Herein, a new method for γ-lactones preparation based on ring contraction was developed. Starting from macrolides, W(OTf) 6 was used to catalyze the ring-opening polymerization then depolymerization. The depolymerization step was not a common ring-closing process, and the carbon number of the ring was reduced one by one by rearrangement to form the most thermodynamically stable five-membered ring compounds. γ-Caprolactone (180 °C for 10 h) was obtained in a yield of 94 % when [EMIM]OTf was used as the solvent, and the yield of isolated product was up to 85 %. The interaction of various components and the reaction mechanism were studied by FTIR spectroscopy and 1 H NMR spectroscopy, respectively. Furthermore, γ-lactones could be produced when the substrate was extended to terminal hydroxyfatty acids. Unexpectedly, the catalyst was poisoned by 1 equivalent of H 2 O added during the process and thus the yield decreased greatly. The reaction is green and simple, and proceeds in one pot with high atom economy (100 % for macrolides and with water as the only byproduct for terminal hydroxyfatty acid), which provides a promising approach to synthesizing γ-lactones.
Asymmetric electrocatalysis is poised to provide a unique avenue for access to enantioenriched molecules that are difficult to obtain through more conventional approaches, but the development of efficient electrocatalysts capable of highly enantioselective transformations remains elusive. Towards this enviable end, bifunctional electrocatalyst capable of both redox mediation and delivery of high stereocontrol is needed. Here we disclose a novel TEMPO-BOX-ligated copper electrocatalyst that enables oxidative kinetic resolution of racemic 1,4-diols, affording diverse chiral 1,4-diols and γ-lactones with good or excellent chemo-, regio, and enantioselectivity. We also show that this cooperative Cu/TEMPO-BOX catalytic strategy is applicable to the electro-oxidative kinetic resolution of 1,2- and 1,3-amino alcohols. This work demonstrates the potential of bifunctional electrocatalysis for asymmetric synthetic methods and we anticipate that it will spur the development of new hybrid electrocatalysts to realize novel asymmetric electrocatalytic methods.
A novel carbonyl reductase from Hyphopichia burtoni ( Hb KR) was discovered by gene mining. Hb KR is a NADPH-dependent dual function enzyme with reduction and oxidation activity belonging to SDR superfamily. Hb KR strictly follows Prelog priority in the reduction of long-chain aliphatic keto acids/esters containing remote carbonyl groups, such as 4-oxodecanoic acid and 5-oxodecanoic acid, producing ( S )- γ -decalactone and ( S )- δ -decalactone in >99 % e.e. Tailor-made engineering of Hb KR was conducted to improve its catalytic efficiency . Variant F207A/F86M was obtained with specific activity of 8.37 U/mg toward 5-oxodecanoic acid, which was 9.7-fold of its parent. Employing F207A/F86M, 100 mM 5-oxodecanoic acid could be reduced into optically pure ( S )- δ -decalactone. Molecular docking analysis indicates that substitution of aromatic Phe with smaller residues renders sufficient space for accommodating substrates in a more stable conformation. This study offers an efficient biocatalyst for the biosynthesis of ( S )-lactones, and provides guidance for engineering carbonyl reductases toward structurally hindered substrates.
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