Intramolecular Hydroamination of Conjugated Dienes Catalyzed by Lewis and Brønsted Acids

Abstract

Intramolecular hydroaminations of conjugated acyclic aminodienes catalyzed by Lewis acids such as silver triflate, cationic gold complexes, BINAP-copper(II) triflate, iron trichloride, indium(III) bromide, iodine and by TfOH, as a representative Brønsted acid, are evaluated. The reaction proceeds in a 1,4-addition manner through a 5-exo-trig cyclization affording the corresponding 2-substituted pyrrolidines, (triphenylphosphite)gold(I) triflate, and TfOH providing the best results.

hydroamination - conjugated dienes - Lewis acids - triflic acid - sulfonamides

References and Notes

For recent reviews, see:

<A NAME="RD33510ST-1A">1a</A> Müller TE. Hultzsch KC. Yus M. Foubelo F. Tada M. Chem. Rev.  2008,  108:  3795 

<A NAME="RD33510ST-1B">1b</A> Wolfe JP. Synlett  2008,  2913 

<A NAME="RD33510ST-1C">1c</A> Shen HC. Tetrahedron  2008,  64:  3885 

<A NAME="RD33510ST-1D">1d</A> Severin R. Doye S. Chem. Soc. Rev.  2007,  36:  1407 

<A NAME="RD33510ST-1E">1e</A> Widenhoefer RA. Han X. Eur. J. Org. Chem.  2006,  4555 

<A NAME="RD33510ST-1F">1f</A> Hazari N. Mountford P. Acc. Chem. Res.  2005,  38:  839 

<A NAME="RD33510ST-1G">1g</A> Hultzsch KC. Adv. Synth. Catal.  2005,  437:  367 

<A NAME="RD33510ST-1H">1h</A> Alonso F. Beletskaya IP. Yus M. Chem. Rev.  2004,  104:  3079 

<A NAME="RD33510ST-2A">2a</A> Under oxidative conditions double cyclization was achieved: Hegedus LS. Winton PM. Varaprath S. J. Org. Chem.  1981,  46:  2215 

<A NAME="RD33510ST-2B">2b</A> Andersson PG. Bäckvall J.-E. J. Am. Chem. Soc.  1992,  114:  8696 

<A NAME="RD33510ST-2C">2c</A> Muñiz K. Streuff J. Chávez P. Hövelmann CH. Chem. Asian J.  2008,  3:  1248 

<A NAME="RD33510ST-3">3</A> For example, see: Hong S. Marks TJ. Acc. Chem. Res.  2004,  37:  673 

<A NAME="RD33510ST-4">4</A> Yeh M.-CP. Pai H.-F. Lin Z.-J. Lee B.-R. Tetrahedron  2009,  65:  4789 

<A NAME="RD33510ST-5">5</A> Julian LD. Hartwig JF. J. Am. Chem. Soc.  2010,  132:  13813 

<A NAME="RD33510ST-6">6</A> Yamamoto H. Shiomi S. Odate D. Sasaki I. Namba K. Imagawa H. Nishizawa M. Chem. Lett.  2010,  39:  830 

<A NAME="RD33510ST-7">7</A> Giner X. Nájera C. Org. Lett.  2008,  10:  2919 

<A NAME="RD33510ST-8">8</A> Giner X. Nájera C. Synlett  2009,  3211 

<A NAME="RD33510ST-9">9</A>

Substrates 1a-c and 2 were synthesized according to Muñiz et al. (ref. 2c) in a slightly modified route. For the synthesis of 1d, see ref. 6.

For the use of Ph₃PAuOTf in the intramolecular hydroami-nation of alkenes, see:

<A NAME="RD33510ST-10A">10a</A> Zhang J. Yang C.-G. He C.
J. Am. Chem. Soc.  2006,  128:  1798 

<A NAME="RD33510ST-10B">10b</A> Han X. Widenhoefer RA. Angew. Chem. Int. Ed.  2006,  45:  1747 

<A NAME="RD33510ST-10C">10c</A> Liu X.-Y. Li C.-H. Org. Lett.  2006,  8:  2707 

<A NAME="RD33510ST-11">11</A> For the use of FeCl₃˙6H₂O in the intramolecular hydroamination of alkenes, see: Komeyama K. Morimoto T. Tataki K. Angew. Chem. Int. Ed.  2006,  45:  2938 

<A NAME="RD33510ST-12">12</A> For the use of (±)-BINAP-Cu(OTf)₂ in the intermolecular hydroamination of alkenes, see: Taylor JG. Whittall N. Hii KK. Org. Lett.  2006,  8:  3561 

<A NAME="RD33510ST-13">13</A> For the use of InBr₃ in the intermolecular hydroamination of alkenes, see: Huang J.-M. Wong C.-M. Xu F.-X. Loh T.-P. Tetrahedron Lett.  2007,  48:  3375 

<A NAME="RD33510ST-14">14</A> For the use of I₂ in the intermolecular hydroamination of alkenes, see: Yadav JS. Reddy SBV. Rao TS. Krishna BBM. Tetrahedron Lett.  2009,  50:  5351 

For pioneering work in the use TfOH for the intramolecular hydroamination of alkenes, see:

<A NAME="RD33510ST-15A">15a</A> Schlummer B. Hartwig JF. Org. Lett.  2002,  4:  1471 

<A NAME="RD33510ST-15B">15b</A> Haskins CM. Knight DW. Chem. Commun.  2002,  2724 

<A NAME="RD33510ST-16">16</A>

Other authors described the fomation of 2-allyl pyrrolidine as a minor product.^²a,³,5

<A NAME="RD33510ST-17">17</A> For a review of the Thorpe-Ingold effect, see: Jung ME. Piizzi G. Chem. Rev.  2005,  105:  1735 

<A NAME="RD33510ST-18">18</A>

Reactions catalyzed by AgOTf and [(PhO)₃P]AuOTf were carried out with light exclusion. (±)-BINAP-Cu(OTf)₂ complex was formed in situ by mixing equimolar amounts of (±)-BINAP and Cu(OTf)₂ for 15 min at the reaction temperature.

<A NAME="RD33510ST-19">19</A>

For hydroamination reactions catalyzed by FeCl₃˙6H₂O, an argon atmosphere was not necessary and HPLC grade DCE was used as solvent.