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Synlett 2011(5): 631-634  
DOI: 10.1055/s-0030-1259680
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Intramolecular Hydroamination of Conjugated Dienes Catalyzed by Lewis and Brønsted Acids

Alejandro Baeza, Carmen Nájera*
Departamento de Química Orgánica, Facultad de Ciencias and Instituto de Síntesis Orgánica (ISO), Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
Fax: +34(96)5903549; e-Mail: cnajera@ua.es;
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Publication History

Received 27 December 2010
Publication Date:
22 February 2011 (online)

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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.

Key words

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

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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.

16

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

18

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.

19

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