Communications
DOI: 10.1002/anie.201003167
Synthetic Methods
Efficient Silver-Catalyzed Regio- and Stereospecific Aziridination of
Dienes**
Josep Llaveria, ꢀlvaro Beltrꢁn, M. Mar Dꢂaz-Requejo,* M. Isabel Matheu,* Sergio Castillꢃn,*
and Pedro J. Pꢄrez*
The synthesis of aziridine derivatives through metal-mediated
nitrene addition reactions to olefins [Eq. (1)] has been
extensively developed in the last decades; quantitative
Scheme 1. Strategies for the synthesis of vinylaziridines. LG=leaving
conversions as well as complete enantioselection have been
already described.[1,2] However, in spite of the large number
of reports related to the alkene aziridination reaction by this
method and the synthetic interest of vinylaziridines,[3] only
few have dealt with conjugated dienes as the substrate.
Copper-,[4] manganese-, and ruthenium-based[5] catalysts have
provided good yields of vinylaziridines formed by the
group.
imines also provides[7] a facile process as it involves the
regioselective construction of vinylaziridine (path b). These
two methods have usually led to the thermodynamically
stable cis aziridines.[8] trans Aziridines were obtained with
high stereoselectivity by the ylide route driving the reaction
under kinetic control conditions.[9] Vinylaziridines were also
prepared from vinyl epoxides by ring opening with azides
(path e), from 1,2-amino halides (path c),[10] and by conjugate
addition.[11] The aforementioned nitrene addition to dienes
(path d)[4,5] have been described, but they can be yet
considered far from successful in terms of regio- and
stereoselectivity.
On the basis of the above, we planned to develop a
catalytic system capable of inducing the formation of vinyl-
aziridines to achieve the following goals: 1) use of non-
symmetric dienes, 2) tolerance to other functional groups,
3) control of the regioselectivity (given an unsymmetric
diene), and 4) control of the stereoselectivity (to obtain
either cis or trans vinylaziridines). We have previously
reported that complexes of general formula [TpxCu(NCMe)]
(Tpx = homoscorpionate ligand,[12] see Scheme 2 for the
structure) effectively catalyze the aziridination of simple
alkenes through the nitrene-transfer reaction,[13] using
PhINTs as the nitrene source. To drive our work to the
above goals, and because the b-amino alcohol moiety is found
in a wide variety of biologically active compounds,[14] we
chose trans,trans-2,4-hexadien-1-ol (1) as the substrate, which
is a nonsymmetric diene containing a hydroxy group.
The reaction of such diene with PhINTs in the presence of
the appropriate catalyst might afford two different aziridines,
from a regioselective point of view, each of them with a cis or
trans geometry (compounds 2–5, Scheme 2). Aziridines 2 and
3 could be formed by nitrene addition to the double bond
vicinal to the hydroxy end of the substrate, whereas aziridines
4 and 5 would correspond to the addition to the double bond
vicinal to the methyl end.
=
exclusive aziridination of one C C bond of the diene,
although with the following limitations: 1) only symmetric
dienes were employed and 2) selectivity, intended as cis/trans
(or trans/cis) ratio, was low. These two drawbacks strongly
prevent the synthetic application of this method.
In fact, vinylaziridines are commonly synthesized by
stoichiometric procedures based on nucleophilic intramolec-
ular substitution. Thus, the Darzens-type reaction (Scheme 1,
path a) is one of the oldest and most flexible methods for
preparation of functional aziridine derivatives including
vinylaziridines.[6] The reaction between an allylic ylide and
[*] ꢀ. Beltrꢁn, Dr. M. M. Dꢂaz-Requejo, Prof. P. J. Pꢃrez
Laboratorio de Catꢁlisis Homogꢃnea, Centro de Investigaciꢄn en
Quꢂmica Sostenible, Departamento de Quꢂmica y Ciencia de los
Materiales, Unidad Asociada al CSIC, Universidad de Huelva
Campus de El Carmen s/n, 21007 Huelva (Spain)
Fax: (+34)95-921-9942
E-mail: perez@dqcm.uhu.es
J. Llaveria, Dr. M. I. Matheu, Prof. S. Castillꢄn
Departament de Quꢂmica Analꢂtica i Quꢂmica Orgꢁnica
Facultat de Quꢂmica, Universitat Rovira i Virgili
C/Marcel·lꢂ Domingo s/n, 43007 Tarragona (Spain)
Fax: (+34)977-558446
E-mail: sergio.castillon@urv.cat
[**] We thank the MICINN (CTQ2008-00042BQU and CTQ2008-
1569BQU) and Consolider Ingenio 2010 (CSD2006-0003) for
funding. J.L. thanks the MICINN and A.B. thanks the Universidad de
Huelva (Plan Propio) for a fellowship.
Supporting information for this article is available on the WWW
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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2010, 49, 7092 –7095