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.

Key words

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

References and Notes

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9

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.