Journal of Organometallic Chemistry 691 (2006) 2159–2161
Communication
Desymmetrisation of bicyclo[4.4.0]decadienes: A planar-chiral
complex proved to be most effective in an asymmetric Heck reaction
a
b
c,
*
Matthias E.P. Lormann , Martin Nieger , Stefan Brase
¨
a
Cynora GmbH, Kaiserstr. 100, D-52134 Herzogenrath, Germany
Institut fu¨r Anorganische Chemie der Rheinischen Friedrich-Wilhelms-Universita¨t Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany
b
c
Institut fu¨r Organische Chemie, Universita¨t Karlsruhe (TH), Fritz-Haber-Weg 6, D-76131 Karlsruhe, Germany
Received 24 August 2005; received in revised form 21 September 2005; accepted 21 September 2005
Available online 23 November 2005
Abstract
The synthesis and desymmetrisation of bicyclo[4.4.0]decadienes is described; the enantioselective Heck reaction using JOSIPHOS as a
planar-chiral complex produces a tetracyclic system with three stereogenic centers in up to 84% enantiomeric purity.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Heck reaction; Desymmetrisation; JOSIPHOS
The desymmetrisation of achiral compounds is an indis-
pensable tool for the synthesis of chiral compounds [1].
Nature uses desymmetrisation to build up complex mole-
cules. While the ring opening of epoxides [2] and oxidation
of double bonds are well established approaches in desym-
metrisation strategies [3], the formation of carbon–carbon
bonds by asymmetric transition-metal catalysis has not
been exhaustively examined [3]. Nevertheless, this method
remains viable because both enantiomers of the complex
molecule are accessible. In particular, the asymmetric intra-
molecular Heck reaction [4], pioneered by Kagechika and
Shibasaki [5a], Ashimori and Overman [5b], and used by
others [4,5c,5d], would result in the formation of complex
molecules.
We were intrigued by the fact that desymmetrisation of
a bicyclic system gives rise to tricyclic systems. The
required bicyclic system was assembled as followed. Start-
ing from naphthalene (1), Birch reduction, epoxidation and
ring-opening led to alcohol 4 [6]. Alkylation was performed
with functionalised benzyl bromides to obtain the required
starting materials 5-X (X = I, Br) in good overall yields.
The triflate 5-OTf and nonaflate 5-ONf were prepared
starting from 5-Br by conversion into the phenol derivate
5-OH and subsequent conversion with trifluoromethane-
sulfonic acid anhydride or nonafluorobutanesulfonic fluo-
ride, to the desired products 5-OTf and 5-ONf, respectively
(Scheme 1).
Heck reaction with iodide 5-I, bromide 5-Br and triflate
5-OTf under various conditions led to the formation of 6
with different results. Its relative stereochemistry was pro-
ven by X-ray crystallography (Fig. 1) [7]. The usual ligands
for asymmetric Heck reactions, BINAP or the oxazoline 9,
led to very low enantioselection or no conversion at all
(Table 1; Scheme 2).
The conversion rates could be increased by the addi-
tion of silver carbonate, but this had almost no positive
effect on the enantiomeric excess. Other ligands ((R)-
PHANEPHOS, (S,S)ET-BPE, ligand 11) were either
inactive or produced tricycles with low stereoinduction
(Fig. 2).
The use of the JOSIPHOS ligand, employed primarily
in hydrogenation reactions, gave a remarkably high enan-
tiomeric excess. Recrystallisation of this product gave a
virtually enantiopure material (Table 1, entry 17). Addi-
tionally, the use of bromide 5-Br gave almost the same
*
Corresponding author. Tel.: +49 721 608 2902; fax: +49 721 608 8581.
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.09.047