2019

Publications

1. Br-radical-mediated [3+2] annulation: synthesis of 2-bromomethylsubstituted alkenylcyclopentanes by the reaction of alkenylcyclopropanes with allyl bromides under photo irradiation

   Fukuyama, T.; Kippo, T.; Hamaoka, K.; Ryu, I.
   Sci. China Chem.. 2019, 62, 1525-1528.
   DOI: 10.1007/s11426-019-9595-0
   
   　A radical chain addition of allyl bromides 2 to alkenylcyclopropanes 1 resulted in [3+2] annulation to give 2-bromomethylalkenylcyclopentanes 3 in good yields (16 examples). In this reaction, two kinetically fast radical reactions, cyclopropylcarbinyl radical-ring-opening and 5-exo-radical cyclization, preceded the β-fragmentation of a bromine radical to make the formal cycloaddition possible.

2. Radical Mediated Aza-Pauson-Khand Reaction of Acetylenes, Imines, and CO Leading to Five-Membered Unsaturated Lactams

   Fukuyama, T.; Okada, T.; Nakashima, N.; Ryu, I.
   Helv. Chim. Acta. 2019, 102, 2254 –2259.
   DOI: 10.1002/hlca.201900186
   
   　Formal [2+2+1] cycloaddition reaction involving acetylenes, aromatic imines, and CO was achieved by radical chain reaction, which gave five-membered unsaturated lactams in modest to good yields. When we used 5-chloropentyne, sequential carbonylation took place accompanied with double annulation events to give a cyclohexanone-fused lactam in excellent stereoselectivity.

3. Vicinal difunctionalization of alkenes by four-component radical cascade reaction of xanthogenates, alkenes, CO, and sulfonyl oxime ethers

   Sumino, S.; Fukuyama, T.; Sasano, M.; Ryu, I.; Jacquet, A.; Robert, F.; Landais, Y.
   Beilstein J. Org. Chem. 2019, 15, 1822-1828.
   DOI: 10.3762/bjoc.15.176
   
   　Four-component coupling reactions between xanthogenates, alkenes, CO, and sulfonyl oxime ethers were studied. In the presence of hexabutylditin, working as a propagating radical reagent, the chain reaction proceeds, as expected, taking into account reagents polarities, affording the corresponding functionalized α-keto oximes. Although yields are modest, this rare one-pot fourcomponent process is easy to carry out and the resulting compounds, bearing multiple functionalities, have the potential for further elaboration.

4. Revisiting Hydroxyalkylation of Phenols with Cyclic Carbonates

   Kao, S.-C.; Lin, Y.-C.; Ryu, I.; Wu, Y.-K.
   Adv. Synth. Catal. 2019, 361, 3639-3644.
   DOI: 10.1002/adsc.201900287
   
   　Described is a tetrabutylammonium fluoride-mediated hydroxyalkylation reaction of phenols with cyclic carbonates. This operationally simple method enables the synthesis of a variety of aryl β-hydroxyethyl ethers in good to excellent yields with a very small amount of catalyst loading (0.1–1 mol%). Of particular note is the efficient conversion of aromatic diols and phloroglucinol to the corresponding bis- and tris-hydroxyethylated products. To further showcase the versatility of this protocol, guaifenesin was prepared with a single step by the condensation of guaiacol and glycerol carbonate. We also developed a flow ethoxylation process permitting the continuous synthesis of multiflorol.

5. Synthesis of 4,4-Difluoroalkenes by Coupling of α‑Substituted α,α-Difluoromethyl Halides with Allyl Sulfones under Photoredox Catalyzed Conditions

   Uno, M.; Sumino, S.; Fukuyama, T.; Matsuura, M.; Kuroki, Y.; Kishikawa, Y.; Ryu, I.
   J. Org. Chem. 2019, 84, 9330-9338.
   DOI: 10.1021/acs.joc.9b00901
   
   　Photoredox-catalyzed allylation of α-gem-difluorinated organohalides with allyl sulfones proceeded smoothly under visible light irradiation to give 4,4-difluoroalkenes in good yields. In the presence of catalytic Ru(bpy)3Cl2, Hantzsch ester, and diisopropylethylamine, the reaction was complete within 2 h. Using the same methodology, three-component cascade reactions to give 6,6-difluoroalkenes were carried out successfully.

6. Bromine-Radical-Mediated Site-Selective Allylation of C(sp3)–H Bonds

   Ueda, M.; Maeda, A.; Hamaoka, K.; Sasano, M.; Fukuyama, T.; Ryu, Ilhyong.
   Synthesis. 2019, 51, 1171-1177.
   DOI: 10.1055/s-0037-1610413
   
   　The C(sp3)–H allylation of alkanes is investigated by using allyl bromides under radical reaction conditions. In many cases, methine C–H allylation preceded methylene and methyl C–H allylation with complete or a high degree of site selectivity. The C–H allylation of allylic compounds, such as allylbenzene, gives 1,5-dienes with the SH2′ reactions of the allyl radicals occurring at the less hindered carbon.

7. Kinetically Controlled Fischer Glycosidation under Flow Conditions: A New Method for Preparing Furanosides

   Masuia, S.; Manabe, Y.; Hirano, K.; Shimoyama, A.; Fukuyama, T.; Ryu, I.; Fukase, K.
   Synlett. 2019, 30, 397-400.
   DOI: 10.1055/s-0037-1611643
   
   　Kinetically controlled Fischer glycosidation was achieved under flow conditions. β-Hydroxy-substituted sulfonic acid functionalized silica (HO-SAS) was used as an acid catalyst. This reaction directly converted aldohexoses into kinetically favored furanosides to enable the practical synthesis of furanosides. After optimization of the reaction temperature and residence time, glucofuranosides, galactofuranosides, and mannofuranosides were synthesized in good yields.

8. Carbonylation of Alkyl Radicals Derived from Organosilicates through Visible-Light Photoredox Catalysis

   Cartier, A.; Levernier, E.; Corc, V.; Fukuyama, T.; Dhimane, A.L.; Ollivier, C.; Ryu, I.; Fensterbank, L.
   Angew. Chem. Int. Ed.. 2019, 58, 1789-1793.
   DOI: 10.1002/anie.201811858.
   
   　Primary, secondary, and tertiary alkyl radicals formed by the photocatalyzed oxidation of organosilicates underwent efficient carbonylation with carbon monoxide (CO) to give a variety of unsymmetrical ketones. This study introduces the possibility of radical carbonylation under a photooxidative regime.