Iron-catalyzed reductive radical cyclization of organic halides in the presence of NaBH4: evidence of an active hydrido iron(I) catalyst.

Iron made'em: iron(II) complexes such as FeCl(2) and [FeCl(2)(dppe)(2) ] (dppe=1,2-bisdiphenylphosphinoethane) are efficient precatalysts for the radical cyclization of unsaturated iodides and bromides in the presence of NaBH(4). Cyclic voltammetry studies suggests that the reaction occurs through a radical mechanism via an anionic hydrido iron(I) species as the key intermediate for the activation of the substrates by electron transfer.

[1]  A. Baba,et al.  Dihaloindium hydride as a novel reducing agent. , 2005, Chemical record.

[2]  C. Chatgilialoglu.  Organosilanes as radical-based reducing agents in synthesis , 1992 .

[3]  H. Shinokubo,et al.  Intramolecular Radical Cyclization of 2-Haloethanal Allyl Acetal and Allyl 2-Halophenyl Ether with a Grignard Reagent in the Presence of Iron(II) Chloride , 1998 .

[4]  B. C. Gilbert,et al.  The use of free radical initiators bearing metal–metal, metal–hydrogen and non-metal–hydrogen bonds in synthesis , 2002 .

[5]  G. Hilt,et al.  Iron-salen complexes as efficient catalysts in ring expansion reactions of epoxyalkenes , 2006 .

[6]  S. Mikami,et al.  Triethylborane-induced radical reactions with gallium- and indium hydrides , 2003 .

[7]  J. Lalevée,et al.  Polarity reversal catalysis in radical reductions of halides by N-heterocyclic carbene boranes. , 2012, Journal of the American Chemical Society.

[8]  J. D. de Vries,et al.  Soluble iron nanoparticles as cheap and environmentally benign alkene and alkyne hydrogenation catalysts. , 2009, Chemical communications.

[9]  L. Fensterbank,et al.  Oxidation of alkyl trifluoroborates: an opportunity for tin-free radical chemistry. , 2010, Angewandte Chemie.

[10]  G. Schuster,et al.  Photoreduction of Substituted Arenes with Borates and Borohydride: An Electron Transfer Mechanism , 1987 .

[11]  Tomoaki Nakamura,et al.  Triethylborane-induced radical reaction with Schwartz reagent. , 2001 .

[12]  M. J. Medeiros,et al.  Electrogenerated Nickel(I) complexes as catalysts for the intramolecular radical cyclisation of unsaturated α-bromoesters , 2004 .

[13]  Alois Fürstner,et al.  The promise and challenge of iron-catalyzed cross coupling. , 2008, Accounts of chemical research.

[14]  E. Nakamura,et al.  Iron-catalyzed C-C bond formation at alpha-position of aliphatic amines via C-H bond activation through 1,5-hydrogen transfer. , 2010, Journal of the American Chemical Society.

[15]  L. Fensterbank,et al.  Visible-light-induced photoreductive generation of radicals from epoxides and aziridines. , 2011, Angewandte Chemie.

[16]  E. Carreira,et al.  Catalytic hydrochlorination of unactivated olefins with para-toluenesulfonyl chloride. , 2008, Angewandte Chemie.

[17]  A. Beckwith,et al.  Homolytic reductive dehalogenation of aryl halides by sodium borohydride , 1986 .

[18]  Alois Fürstner.  Aus dem Schatten ins Rampenlicht: Eisen(‐Domino)‐Katalyse , 2009 .

[19]  E. Duñach,et al.  Carbon−Carbon Bond Formation with Electrogenerated Nickel and Palladium Complexes , 2003 .

[20]  M. Aresta,et al.  Hidrido-complexes of iron(IV) and iron(II) , 1971 .

[21]  I. Ciofini,et al.  First Evidence of the Oxidative Addition of Fe0(N,N)2 to Aryl Halides: This Precondition Is Not a Guarantee of Efficient Iron‐Catalysed C–N Cross‐Coupling Reactions , 2011 .

[22]  F. Neese,et al.  Catalysis via homolytic substitutions with C-O and Ti-O bonds: oxidative additions and reductive eliminations in single electron steps. , 2009, Journal of the American Chemical Society.

[23]  John C. Walton,et al.  Flucht vor der Tyrannei des Zinns: auf der Suche nach metallfreien Radikalquellen , 1998 .

[24]  Y. Tu,et al.  Iron-catalyzed C(sp3)-C(sp3) bond formation through C(sp3)-H functionalization: a cross-coupling reaction of alcohols with alkenes. , 2009, Angewandte Chemie.

[25]  A. Baba,et al.  Indium(III) chloride-sodium borohydride system: a convenient radical reagent for an alternative to tributyltin hydride system. , 2002, Journal of the American Chemical Society.

[26]  T. Fukuyama,et al.  Tin-free Giese reaction and the related radical carbonylation using alkyl iodides and cyanoborohydrides. , 2008, Organic letters.

[27]  L. Zani,et al.  Iron-catalyzed reactions in organic synthesis. , 2004, Chemical reviews.

[28]  J. Norton,et al.  Initiating radical cyclizations by H transfer from transition metals , 2008 .

[29]  T. Taniguchi,et al.  Iron-catalyzed redox radical cyclizations of 1,6-dienes and enynes. , 2010, Organic letters.

[30]  A. Fürstner.  From oblivion into the limelight: iron (domino) catalysis. , 2009, Angewandte Chemie.

[31]  S. Davis,et al.  Iron nanoparticles in the coupling of alkyl halides with aryl Grignard reagents. , 2006, Chemical communications.

[32]  M. White,et al.  A Predictably Selective Aliphatic C–H Oxidation Reaction for Complex Molecule Synthesis , 2007, Science.

[33]  T. Fukuyama,et al.  Black-light-induced radical/ionic hydroxymethylation of alkyl iodides with atmospheric CO in the presence of tetrabutylammonium borohydride. , 2010, Organic letters.

[34]  G. Hilt,et al.  An iron-catalysed chemo- and regioselective tetrahydrofuran synthesis. , 2005, Chemical communications.

[35]  T. Taniguchi,et al.  Iron-mediated radical nitro-cyclization reaction of 1,6-dienes. , 2010, Organic letters.

[36]  A. Baba,et al.  Triethylsilane-indium(III) chloride system as a radical reagent. , 2004, Organic letters.

[37]  L. Fensterbank,et al.  Titanocene-mediated homolytic opening of epoxysilanes , 2006 .

[38]  J. Walton,et al.  Flight from the Tyranny of Tin: The Quest for Practical Radical Sources Free from Metal Encumbrances. , 1998, Angewandte Chemie.

[39]  J. Schwartz,et al.  Titanium catalyzed reduction of aromatic halides by sodium borohydride , 1995 .

[40]  J. Norton,et al.  Tin-free and catalytic radical cyclizations. , 2007, Journal of the American Chemical Society.

[41]  Anna Hedström,et al.  Mechanistic Investigation of Iron‐Catalyzed Coupling Reactions , 2009 .

[42]  Araceli G. Campaña,et al.  Water: the ideal hydrogen-atom source in free-radical chemistry mediated by Ti(III) and other single-electron-transfer metals? , 2006, Angewandte Chemie.

[43]  H. Nöth,et al.  Zur Kenntnis von Di‐cyclopentadienyl‐titan(III)‐Verbindungen, I. Das Di‐cyclopentadienyl‐titan(III)‐boranat, (C5H5)2TiBH4 , 1960 .

[44]  A. Gansäuer,et al.  Reagent-controlled transition-metal-catalyzed radical reactions. , 2000, Chemical reviews.

[45]  D. Curran,et al.  Complexes of borane and N-heterocyclic carbenes: a new class of radical hydrogen atom donor. , 2008, Journal of the American Chemical Society.

[46]  A. Jutand,et al.  Contribution of electrochemistry to organometallic catalysis. , 2008, Chemical reviews.

[47]  D. Curran,et al.  Radical deoxygenation of xanthates and related functional groups with new minimalist N-heterocyclic carbene boranes. , 2010, Organic letters.

[48]  P. Renaud,et al.  Organoboranes as a source of radicals. , 2001, Chemical reviews.

[49]  A. Fürstner,et al.  Preparation, structure, and reactivity of nonstabilized organoiron compounds. Implications for iron-catalyzed cross coupling reactions. , 2008, Journal of the American Chemical Society.

[50]  J. Kochi,et al.  Vinylation of Grignard reagents. Catalysis by iron , 1971 .