Metal-Mediated Carbocyclic Construction: The Kobayashi Synthesis of (+)-Fomitellic Acid B
Jin K. Cha of Wayne State University described (J. Org. Chem. 2009, 74, 5528. ) the diastereoselective intramolecular cyclopropanation of nitriles with homoallylic alcohols such as 1. Valery V. Fokin of Scripps/LaJolla found (J. Am. Chem. Soc. 2009, 131, 18034. ) that the diazoimine derived from 4 could add with high enantioselectivity to aryl alkenes, including styrene 5.
Andreas Gansäuer of the University of Bonn optimized (Angew. Chem. Int. Ed. 2009, 48, 8882, ; Tetrahedron 2009, 65, 10791, ) a Ti catalyst for the cyclization of substrates such as 7 to the corresponding cyclobutanes. F. Dean Toste of the University of California, Berkeley devised (J. Am. Chem. Soc. 2009, 131, 9178. ) a gold catalyst for the enantioselective ring expansion of a prochiral allene such as 9 to the cyclobutanone 10.
David J. Procter of the University of Manchester developed (J. Am. Chem. Soc. 2009, 131, 15467. ) the SmI2-mediated cyclization of a lactone such as 11 to the cyclopentanone 12. Shigeki Matsunaga and Masakatsu Shibasaki of the University of Tokyo designed (Chem. Commun. 2009, 5138. ) a Ni catalyst for the enantioselective condensation of 13 with formaldehyde. Some acyclic β-keto esters could also be hydroxymethylated with high enantiocontrol. Darren J. Dixon, of the University of Oxford, devised (J. Am. Chem. Soc. 2009, 131, 9140. ) a Cu catalyst for the enantioselective Conia cyclization of 15 to 16. K. C. Nicolaou, also of Scripps/La Jolla, reported (Angew. Chem. Int. Ed. 2009, 48, 6293. ) a Rh catalyst for the related cyclization of 17 to 18.
Ryo Shintani and Tamio Hayashi of Kyoto University showed (J. Am. Chem. Soc. 2009, 131, 13588. ) that a Rh catalyst could effect enantioselective conjugate addition of a tetraaryl borate even to a 3-substituted cyclohexenone 19, to establish the cyclic quaternary center. Alexandre Alexakis of the University of Geneva established (Chem. Commun. 2009, 3868. ) that with an easily ionized racemic allylic bromide 21, Cu-mediated coupling with the alkyl Grignard 22 proceeded with substantial asymmetric induction. Jon D. Rainier of the University of Utah devised (Org. Lett. 2009, 11, 3774. ) conditions for effecting Ti-mediated intramolecular metathesis between an alkene and a lactam carbonyl, to give the cyclic enamide 24. Jhillu Singh Yadav of the Indian Institute of Chemical Technology, Hyderabad and René Grée of the Université de Rennes 1 effected (Chem. Commun. 2009, 4717. ) isomerization of the alkenyl ether 26 to the ethyl ketone, leading, via intramolecular aldol condensation and dehydration, to the enone 27.
In the course of a total synthesis of the DNA polymerase inhibitor (+)-Fometillic Acid B (30), Susumu Kobayashi of Tokyo University found (Tetrahedron Lett. 2009, 50, 6764. ) that the Ti (III) reagent developed by W. A. Nugent and T. V RajanBabu effected cyclization of 28 to 29. The alternative diastereomer of the secondary acetate did not cyclize efficiently.