Jump to main content
Jump to site search

Issue 12, 2009
Previous Article Next Article

PdII-promoted [2 + 3] cycloaddition of pyrroline N-oxide to organonitriles. Application of (Δ4-1,2,4-oxadiazoline)-PdII complexes in the Suzuki–Miyaura reaction

Author affiliations

Abstract

[2 + 3] Cycloaddition reactions of the organonitriles RCN 1 (R = Me (1a), Et (1b), p-IC6H4 (1c), p-BrC6H4 (1d), p-ClC6H4 (1e), p-FC6H4 (1f)) with the pyrroline N-oxideO+[upper bond 1 start]N[double bond, length as m-dash]CHCH2CH2C[upper bond 1 end]Me22 in the presence of PdCl2 proceed at room temperature for 12 h and allow the isolation of the corresponding palladium(II) complexes trans-[PdCl2{[upper bond 1 start]N[double bond, length as m-dash]C(R)O[lower bond 1 start]NC[upper bond 1 end](H)CH2CH2C[lower bond 1 end]Me2}2] 3a–3f containing fused bicyclic Δ4-1,2,4-oxadiazoline ligands, in good to excellent yields (75–90%). Treatment of trans-[PdCl2(EtCN)2] with the nitrone 2 in acetone or propionitrile at room temperature affords, in good yield, 3b (R = Et), confirming that complexes 3 are formed vianitrile activation by coordination. These reactions proceed with high diastereoselectivity and afford mixtures of enantiomers, due to the rigid conformation (E) of the cyclic nitrone 2. The oxadiazolines [upper bond 1 start]N[double bond, length as m-dash]C(R)O[lower bond 1 start]NC[upper bond 1 end](H)CH2CH2C[lower bond 1 end]Me2 (R = Et (4b), p-FC6H4 (4f)) are liberated upon reaction of complexes 3b,3f with a diphosphine (dppe). During the liberation of 4f, the complex trans-[PdCl2{[upper bond 1 start]N[double bond, length as m-dash]C(NHCOC6H4F-4)CH2CH2C[upper bond 1 end]Me2}2] 5 was formed in a minor amount upon N–O bond cleavage of the oxadiazoline ring to give a pyrrolylbenzamide species coordinated by the N-atom of the pyrrolyl moiety. The compounds were characterized by IR, 1H and 13C NMR spectroscopies, ESI-MS, elemental analyses and, in the cases of 3b, 3d and 5, also by X-ray diffraction analyses. Complexes 3b and 3f show a high catalytic activity towards the microwave-assisted Suzuki–Miyaura cross-coupling reaction in aqueous medium, achieving a TON value of 2.7 × 105 and a TOF value of 1.1 × 106 h−1.

Graphical abstract: PdII-promoted [2 + 3] cycloaddition of pyrroline N-oxide to organonitriles. Application of (Δ4-1,2,4-oxadiazoline)-PdII complexes in the Suzuki–Miyaura reaction

Back to tab navigation

Supplementary files

Publication details

The article was received on 12 Aug 2008, accepted on 01 Dec 2008 and first published on 06 Feb 2009


Article type: Paper
DOI: 10.1039/B813996B
Citation: Dalton Trans., 2009,0, 2210-2216
  •   Request permissions

    PdII-promoted [2 + 3] cycloaddition of pyrroline N-oxide to organonitriles. Application of (Δ4-1,2,4-oxadiazoline)-PdII complexes in the Suzuki–Miyaura reaction

    J. Lasri, M. F. C. G. da Silva, M. N. Kopylovich, S. Mukhopadhyay, M. A. J. Charmier and A. J. L. Pombeiro, Dalton Trans., 2009, 0, 2210
    DOI: 10.1039/B813996B

Search articles by author

Spotlight

Advertisements