ORGANIC
LETTERS
2
012
Vol. 14, No. 3
94–897
Regioselective, Stereoselective, and
Conformationally Controlled Synthesis
8
4
of (η -Tetraarylcyclobutadiene)-
5
(
η -carbomethoxycyclopentadienyl)-
cobalt Metallocenes
†
Doyle J. Cassar, Elisabeth Nagaradja, David C. D. Butler, Didier Villemin, and
†,‡
§,
‡
,†
Christopher J. Richards*
School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, United Kingdom,
Laboratoire de Chimie Mol eꢀ culaire et Thioorganique, UMR CNRS 6507, INC3M, FR
3
038, labex EMC3, ENSICAEN 14050 Caen, France, and The School of Biological and
Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1
NS, United Kingdom
4
Received December 21, 2011
ABSTRACT
4
5
The FriedelꢀCrafts reaction of (η -tetraphenylcyclobutadiene)(η -carbomethoxycyclopentadienyl)cobalt with acid chlorides/aluminum chloride
resulted exclusively in para-phenyl acylation. Both monoacylated (1.1 equiv of RCOCl/AlCl ) and tetraacylated products (>4 equiv of RCOCl/AlCl
3 3
were synthesized. Reaction of PhCC(o-RC ) (R = Me, i-Pr) with Na(C CO Me) and CoCl(PPh ) gave predominantly (η -1,3-diaryl-2,4-
3
3
)
4
6
H
4
5
H
4
2
5
diphenylcyclobutadiene)(η -carbomethoxycyclopentadienyl)cobalt metallocenes (1,3-[trans] vs 1,2-[cis] selectivity up to 6:1). Conformational
control of FriedelꢀCrafts reactions on the major isomers gave exclusively para-acylation of the unsubstituted phenyl groups.
4
5
(
cobalt 1 is an air and moisture stable metallocene readily
η -Tetraphenylcyclobutadiene)(η -cyclopentadienyl)-
have resulted in a number of specific applications. Exam-
ples include the use of 1,2-disubstituted planar chiral
derivatives of 1 as reagents and catalysts in asymmetric
1
synthesized from diphenylacetylene (Scheme 1). The size
and geometry of 1, together with the relatively electron-
deficient cyclopentadienyl ring, differ from ferrocene and
2
synthesis, and the incorporation of cobalt metallocenes
3
4
into dendrimers, square-grid monomers, and molecular
5
rotors and gears. Some of these studies have employed
6
†
tetraaryl derivatives of 1, readily synthesized from the
3,4,7
corresponding diarylacetylene.
University of East Anglia.
ENSICAEN.
Queen Mary, University of London.
‡
§
Current address: Ontorii, Inc. 419 Western Avenue, Boston, MA 02135,
USA.
(3) Waybright, S. M.; McAlpine, K.; Laskoski, M.; Smith, M. D.;
Bunz, U. H. F. J. Am. Chem. Soc. 2002, 124, 8661.
(4) (a) Harrison, R. M.; Brotin, T.; Noll, B. C.; Michl, J. Organome-
(
1) (a) Nakamura, A.; Hagihara, N. Bull. Chem. Soc. Jpn. 1961, 34,
52. (b) Rausch, M. D.; Genetti, R. A. J. Org. Chem. 1970, 35, 3888.
2) (a) Array ꢀa s, R. G.; Manche n~ o, O. G.; Carretero, J. C. Chem.
4
tallics 1997, 16, 3401. (b) Brotin, T.; Pospı
ꢁs il, L.; Fiedler, J.; King, B. T.;
´
(
Commun. 2004, 1654. (b) Roca, F. X.; Motevalli, M.; Richards, C. J.
J. Am. Chem. Soc. 2005, 127, 2388. (c) Review: Nomura, H.; Richards,
C. J. Chem. Asian J. 2010, 5, 1726. (d) Cannon, J. S.; Kirsch, S. F.;
Overman, L. E. J. Am. Chem. Soc. 2010, 132, 15185. (e) Cannon, J. S.;
Kirsch, S. F.; Overman, L. E.; Sneddon, H. F. J. Am. Chem. Soc. 2010,
Michl, J. J. Phys. Chem. B 1998, 102, 10062.
(5) Zheng, X.; Mulcahy, M. E.; Horinek, D.; Galeotti, F.; Magnera,
T. F.; Michl, J. J. Am. Chem. Soc. 2004, 126, 4540.
(6) Stevens, A. M.; Richards, C. J. Tetrahedron Lett. 1997, 38, 7805.
(7) Nguyen, H. V.; Yeamine, M. R.; Amin, J.; Motevalli, M.;
Richards, C. J. J. Organomet. Chem. 2008, 693, 3668.
132, 15192.
1
0.1021/ol203415r r 2012 American Chemical Society
Published on Web 01/24/2012