Stereocontrolled Carbocyclic Construction: The Mulzer synthesis of (-)-Penifulvin A
Tanmaya Pathak of the Indian Institute of Technology, Kharagpur devised (J. Org. Chem. 2009, 74, 2710. ) a preparation of enantiomerically-pure oxygenated cyclopropanes such as 3 from carbohydrate precursors. Andrei K. Yudin of the University of Toronto established (Org. Lett. 2009, 11, 1281. ) a route to aminated cyclobutanes such as 5 based on sigmatropic rearrangement of the β-lactam 4.
Stephen C. Bergmeier of Ohio University reported (Tetrahedron 2009, 65, 741. ) a study of the balance between five- and six-membered ring formation in the cyclization of aziridines such as 6. Professor Bergmeier also described (Tetrahedron Lett. 2009, 50, 1261. ) the bridging additions of enones to cyclic allyl silanes such as 8. This is particularly interesting, as 8 is easily prepared by Birch reduction of the corresponding phenyl silane.
Ullrich Jahn of the Academy of Sciences of the Czech Republic observed (Chem. Eur. J. 2009, 15, 58. ) that the free-radical cyclization of 11 proceeded to give mainly the diastereomer 12 (~ 1:1 at the secondary allylic position). Daesung Lee of the University of Illinois at Chicago reasoned (J. Am. Chem. Soc. 2009, 131, 8413. ) that the stereochemical relationship between the O and the adjacent C-H of 13 was such that the C-H would be deactivated. The cyclization of the alkylidene carbene derived from 13 indeed proceeded to give 14, setting the stage for the synthesis of platensimycin.
Marco A. Cufolini of the University of British Columbia found (Org. Lett. 2009, 11, 1539. ) an easy protocol for the generation of a nitrile oxide and subsequent dipolar cycloaddition, by oxidation of the oxime. In a related investigation, Adam J. M. Burrell and Iain Coldham of the University of Sheffield cyclized (Org. Lett. 2009, 11, 1515. ) the oxime derived from 18, by way of the intermediate nitrone, to give 19 with high diastereocontrol.
Toshio Honda of Hoshi University established (J. Org. Chem. 2009, 74, 3424. ) that the intramolecular Sakurai cyclization of 20 proceeded with high diastereocontrol, to give 21. Kiyoshi Tomioka of Kyoto University showed (Org. Lett. 2009, 11, 1631. ) that the chiral ligand 24 directed the absolute course of the cascade addition of 23 to 22. The product 25 was carried on to (-)-Lycorine.
Pauline Chiu of the University of Hong Kong devised (J. Am. Chem. Soc. 2009, 131, 4556. ) conditions for the cyclization of the epoxide 26 to 27, with the enantiomerically-pure epoxide controlling the absolute configuration of the tricyclic ring system. Timo V. Ovaska of Connecticut College set (Org. Lett. 2009, 11, 2715. ) the absolute configuration of 28 by Itsuno-Corey reduction of the corresponding ketone. Cascade cyclization then delivered 29. Tanja Gaich and Johann Mulzer of the University of Vienna designed (J. Am. Chem. Soc. 2009, 131, 452. ) a short route to the dioxafenestrane insecticide (-)-Pentifulvin A (32). Photocyclization converted the alcohol 30 to a ~ 1:1 mixture of regioisomers. Reduction of one of them gave 31, which was oxidized to 32.