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Construction of Carbon Frameworks with the Help of Ruthenium Complexes 1 5-Cyclooctadiene as a Reagent in Transition Metal Catalyzed Reactions.

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HIGHLIGHTS
coinpound This would cxpand the possibilities for the crcation of new libraries.
171 C. Y Cho. E. J. Moran. S. R. Chci-I-).J. C Steplians. S. P A. Fodor. C.L.
Adams. .4 Sundaram, J. 6'.Jacobs. P. G. Schultz. Smww 1993. 261.
1303.
[8] S. Hobbs DeWilt. J. S. Kiely. C. J. Stankovic. M . C. Schrocder. D M Reynolds
Cody. M . R. Pa\ia. Pror.. .z'iiil. A < o d S < i .L S A 1993. 90. 6909.
[9] The anlisense oligonucleotides are a n earlier category of "uniiatiiral biopolyiners". A . Peyman. C/irw. Rcjr. 1990. YO. 543.
[lo] S . P. A. Fodor. J. L. Leightoii Read, M . C. Piri-imp. L. Strqer. A T Lu. D.
Solas. S&iiw 1991. 3.71. 767. a highlight \ + a s deboted to this topic: G. von
Kicdcrowksi. A q e w C h w . 1991. I(J3.X39: A i i g r b i . C i i o i z . I i i r . Ed. Ei?g/. 1991,
3(/. 822
[ 1 1 ] This is one the critic;d questions raised iii the highlight by von Kiederowski
[101.
[I?] H M. Gcysen. R. H. Meloen. S. J. Barteling. Pror. ?/a//.Amd. SU. CS.4 1984.
X I , 3998.
[13] B. A Bunin. J. A . Ellman. J Ant. Chrw Six. 1992. / I d . 10997.
[14] R. M. J. Liskamp. W J. Moree. unpublished results.
[15] Peptoids were recently highlighted by H. Kessler. . 4 r i , q v Chrrii. 1993. /(I.<,
572: Air,qcii.. C./ii,ifi. 1171. Ed. Efi,?/ 1993, 32. 543.
[I61 See for example the rccent review o n peptidoinimetics: A. Giannis. T. Kolter.
A i f , q r i i . C/wii?.1993, 105. 1303, A i i g e i i . C/zeiv I i i / . Ed. Eiigl. 1993. 32. 1144.
[17] A highlight was devoted to the "rationality of random screening":
Pluckthun, L. Ge. .3iigor. Chmii. 1991. 103. 301 ; .411,gri1.C h m . I n r . Ed Ennpl.
1991, .W, 296.
Construction of Carbon Frameworks with the Help of Ruthenium Complexes :
1,5-Cyclooctadiene as a Reagent in Transition Metal Catalyzed Reactions
Holger Butenschon"
A communication by B. M. Trost et al.['] which appeared last
year is one of several important papers that have been published
recently from the rapidly developing area of ruthenium -organic chemistry. 1.5-Cyclooctadiene (COD) is frequently used in
transition metal complexes as a bidentate. neutral ligand, which
can be removed again often under mild conditions with the
formation of free coordination sites. The perfect example of this
is bis( 1.5-cyclooctadiene)nickel(o) as a precursor of "naked
nickel". with which G . Wilke et al. carried out a large number
of important reactions and thus emphasized the special value of
organometallic chemistry for the synthesis of organic compounds at a very early stage.I2l It is noteworthy that there have
been very few reports on the reactions of COD at the metal
center despite its frequent use as a ligand. One such example is
the formation of the bicyclo[3.3.0]octadienylcobalt complex 1 from the reaction of
cobalt reagents with COD, as reported by
Lehmkuhl et al. as well as Otsuka et
$0
P
1
aI.w51
R'
2
4
v
Scheme 1. a ) 5 % [CpRu(COD)CI] (3). MeOH: R' = Me. Et. CH,OSi(iPr),.
p-CH,C,H,OCH,.
H: R' = CH,OH. CH,OSi(iPr),. C H 2 C H 2 0 H . />CH,C,H,OCH,. CO,Me. CH,CH2CH,C0,Me. 78-100% (see text)
ficient alkynes react particularly slowly and no reaction takes
place with dimethyl butynedioate. Steric hindrance slows down
the reaction; 5 is obtained only in 51 YO(98 % brsm) after 80 h
at reflux. This can. however. be used for the differentiation of
triple bonds in alkynes with several triple bonds, as shown by
the selective formation of 6 in 63 % (72% brsm, Scheme 2).
Q"
The relatively narrow spectrum of the
organic chemistry of COD has been considerably extended by B. M. Trost et a1."'
who discovered that COD can formally function a s a bis-homodiene in metal-catalyzed [4 + 2]cycloadditions. A 0.1 M solution
Ho%
of the alkyne 2 reacts with 1.1 equivalents of COD in the presence of 5 mol Yo chloro(q"-cycl~octadiene)(~~~-cyclopentadi- The catalytic cycle proposed by the authors starts from a
enyl)rutheniuni(ii) [CpRu(COD)CI] (3)["]in boiling methanol to
cationic cyclopentadienylruthenium complex. bearing one C O D
give derivatives 4 of tricyclo[4.2.2.0'. 'Idec-7-ene (Scheme 1 ) .
ligand and one solvent molecule. The latter is displaced by the
Yields of between 78 and 100% are achieved in seven out of
alkyne, which subsequently reacts with a double bond of the
eight examples, in the other case the yield is only 22 YO(however,
COD ligand to give a metallacyclopentene. An intramolecular
as the authors note, this is in fact "65X0 yield brsm". where brsm
carbometalation of the remaining double bond of the eightstands for "based on recovered starting material"). Electron-demembered ring with successive reductive elimination leads to
the elimination of the products 4; renewed complexation of a
[*I Prof. Dr. H Butenrchdn
COD molecule regenerates the catalytically active species. The
lnstitu[ fur Orgmische Chemie der Universitit
authors point out that the reaction is also catalyzed by other
Schneiderberp 1B. D-30167 Hannobcr (FRG)
coordinatively highly unsaturated ruthenium complexes and fiT e l e f n Int. code + (511)762-.30lI
@)
HIGHLIGHTS
nally make the important remark that the ease of the reactions
observed by them suggests that a range of other ruthenium-catalyzed reactions of C O D may well be possible. They assume that
the coordination properties of COD cannot only be derived
from the entropic effect of the spatial arrangement of the two
double bonds in COD. Possibly electronic effects similar to
those in norbornadiene exist in an attenuated form in COD.
This is in agreement with the fact that the dienes 7-9 d o not
undergo the reaction found with COD."]
7
9 '
8
The ruthenium catalyst 3 was recently used by B. M. Trost et
al. also for coupling reactions of alkenes 10 with alkynes Il.[sl
These reactions lead to the branched coupling products 12 as
well as the linear isomers 13 (Scheme 2). The yields lie between
'
R
w+
Also in these reactions the authors assume that a cationic
cyclopentadienylruthenium complex is the catalytically active
species, the only difference here being that in addition to the
chloro ligand also the C O D ligand is decomplexed and all three
free coordination sites are filled by readily displaceable solvent
molecules. After the complexation of the alkene component, the
latter is transformed into an allyl ligand and the hydrogen atom
released is bound to the metal as a hydrido ligand. After coordination, the alkyne is either intramolecularly hydrometalated or
carbometalated starting from the allyl ligand. From both intermediates the reaction product, still coordinated to ruthenium,
can be easily formed, which is then released with the regeneration of the above-mentioned catalytically active species.
Several years ago B. M. Trost et aI.l9]reported on the coupling
of terminal alkynes 17 with allyl alcohols 18 in the presence of
NH,PF,. This reaction is catalyzed by [ (PPh,),CpRuCI] and
leads to the formation offii-unsaturated ketones 19 (Scheme 4).
A mechanistic study reveals that vinylidene complexes are
formed as intermediates from the terminal alkynes." Also ally1
alcohols can be isomerized with [ (PPh3)2CpRuCI] directly to
give saturated ketones." Interestingly. compound 3, which is
different from [(PPh,),CpRuCI] only in that instead of the two
phosphane ligands a COD ligand is present, catalyzes the coupling of alkynes 17 and allyl alcohols 18 in 51 - 8 5 % yields to
give ;&unsaturated ketones 20 and 21 (Scheme 4).["]
11
10
+yR1
& d
n
RRR
3
+
R
17
\
1
18
a)
13
12
R
OH
T
20
1
+
Scheinc 2. a) 5 % 3. dimethylformarnide (DMF).'H,O 7 . 1 , 100 C, 2 h ; R = Bu,
CH,CH,OH. COMe. (CH,),CO,Me: R' = Pr. CH,OTBDMS, C0,Et: 60--90%.
60 and YO YO,and in most cases the branched isomer 12 is formed
preferentially (12:13 up to 6: 1). Substituents at the propargyl
position of 11 reduce the regioselectivity. and the presence of
propargylic oxygen substituents even leads to an inversion of the
selectivity in favor of the linear coupling products. The
chemoselectivity of the reaction is impressively underlined by
the reaction of 14 with the np-unsaturated ester 15 to give exclusively 16 i n 70% yield (Scheme 3 ) .
0
0
15
14
21
Scheme4. a)6%[(PPh,),CpRuC1],10%NH,PF,.100 C . 10 h.44 7 4 ' % : h ) 1 0 %
3, 10-20%, NH,PF,. 100 C . 1-2 h: R = C,,,H,,. C,H,,.CH(OH)C,H,,.
C(C,H,)(OH)C,H,,: R 1 =Me. iPr. cyclohexyl. C,,HZ,: 51 XS 5'".
From the fact that in the reaction catalyzed by 3 also internal
alkynes 22 can react to give ketones 23 (Scheme 5 ) . the authors
conclude that in this case no vinylidene complex acts as an
intermediate. Apparently, its formation is favored by the presence of phosphane ligands, and in their absence other reaction
paths are followed. The regioselectivity ofthe reaction as well as
its yield can be increased if a mixture of water and DMF is used
as solvent. The reaction functions also with alkynes whose triple
bond is conjugated to an ester group. The chemoselectivity of
the reaction was demonstrated by the coupling of a steroid side
R
0
16
Scheme
3
'1)
5"/. 3 D M F H,O 3 1. 100 C. 2 h. 7 0 %
,411gi~ii( ' l i i w i In/. Ed. E n d . 1994. 3.3. N o . 6
A
I
22
18 (R' = CH,)
Scheme 5 a) 10% 3.10-20% NH,PF,
i' VCH Verlujisjiesrlldluf!m h H , 0-69481 Weinheim, I994
23
100 C 1 2 h. R = Bu ( 4 5 % ) Ph ( 5 0 % )
0570-OK3~:94:0606-0637S 10.00
+ .?.T.lI
631
HIGHLIGHTS
chain with an ally1 alcohol; one ab-unsaturated carbonyl functionality present in the steroid part remained unaltered.
The significance of ruthenium-catalyzed reactions is also emphasized by a very recent publication by T. Mitsudo et al.,[13]
who achieved [2 + 2]cycloadditions of norbornene 25 and norbornadiene 28 with a range of alkynes 26. These reactions are
catalyzed by chloro(q4-cyclooctadiene)(~5-pentarnethylcyclopentadienyl)ruthenium(II) [Cp*Ru(COD)CI] (24)[14’ and give
27 and 29, respectively in good yields (Scheme 6). Ru-catalyzed
27
26
25
28
29
30 (R’ = H)
Scheme 6. a) 5 % [Cp*Ru(COD)Cl] 24,80”C, 15-20 h, NEt,, R, R’ = Me, Et, Ph,
C J , , , CH(OEt),, CO,Me, CO,Et, 40-88%; b) 5 % 24, 100”C, 24-120h. R,
R = H, Me, Ph. C0,Me. CO,Et, C,H,,, C,,H,,. 23-87% 29, 12-26% 30
(R’ = H).
[2 + 2]cycloadditions of norbornene with butynedioates have
been known for a long time.” 16] However, what is new is that
the reaction, which was successful with other ruthenium catalysts only with butynedioates, now functions with a whole series
of different alkynes, and that not only norbornene 25, but also
norbornadiene 28 can be used. In this way in the course of the
reaction [Cp*RuCl(nbd)] (nbd = norbornadiene) is formed,
which is more stable than 3. Thus, slightly higher reaction temperatures are required for reactions with norbornadiene. In addition to the adducts 29 to norbornadiene, meta-disubstituted
arenes 30 are also formed. The use of phenylethyne which is
deuterated at the terminal alkyne position reveals that the additional C, building block present in 30 stems from norbornadiene. In agreement with a retro-Diels -Alder reaction, di(cyclopentadiene) was detected in the reaction mixtures.
As a possible mechanism for the reaction the authors propose
that 24 releases the C O D ligand with the formation of the catalytically active species and the two free coordination sites are
then filled by norbornadiene and the alkyne. From this a metal’3
638
i(]
VCH VerlugAge~ellsthuftnibH. 0-69451 Wmhcrm. 1994
lacyclopentene is formed, which either reacts by reductive elimination to give the [2 + 2]cycloadduct or by insertion of a further alkyne molecule forms a metallacycloheptadiene. The latter
then releases cyclopentadiene in a retro-Diels- Alder reaction
and is thus transformed into the metallacycloheptatriene, the
direct precursor of 30.
Interestingly, the only difference between the catalysts used
by B. M. Trost et al. (3) and T. Mitsudo et al. (24) is that an
unsubstituted cyclopentadienyl ligand is present in 3 and a pentamethylcyclopentadienyl ligand in 24. The electronic and steric
differences of the two ligands are well known; in light of the
papers presented here the question arises as to how the spectrum
of ruthenium-catalyzed reactions may be extended by the use of
a new ligand recently described by P. Gassman et a1.;1171
the title
of the work read as follows: “1,2,3,4-Tetramethyl-5-(trifluoromethy1)cyclopentadienide : A Unique Ligand with the Steric
Properties of Pentamethylcyclopentadienide and the Electronic
Properties of Cyclopentadienide”.
That the Cp*Ru fragment can also be used to break down
carbon frameworks was shown at the beginning of 1993 by B.
Chaudret et aI.[’*’, who, using an example from steroid chemistry, achieved the elimination of methane from a methyl-substituted cyclohexadiene with consequent aromatization.
German version: Angew C h m . 1994, 106, 664
[l] B. M. Trost, K. h i . A. F. Indolese, J. Am. Chem. Sot.. 1993. 115, 8831-8832.
[2] Summary: G. Wilke, Angerr. Chem. 1988, 100, 189-211; Angew. Chem. h i .
Ed. Engl. 1988.27, 185-206.
[3] S . Otsuka. T. Tdketomi, J. Chem. Soc. Dulran Trans. 1972, 1879-1882.
[4] H. Lehmkuhl, H . W. Leuchte. E. Janssen, J. Orgunomer. Chem. 1971.30.407409.
[5] H. W. Leuchte, Dissertation, UniversitPt Bochum, 1971.
[6] M. 0 . Albers, D. J. Robinson, A. Shaver, E. Singleton, Organome/aNics 1986,
5. 2199-2205
[7] B. M. Trost. personal communication.
[ S ] 8. M. Trost, A. Indolese, J. A m . Cliem. SOC.1993, 1 15. 4361 -4362.
191 B. M. Trost. G. Dyker, R. 3. Kulawiec, J. A m . C h m . Sot.. 1990, 112, 7x097811.
[lo] B. M. Trost. R. J. Kulawiec, J. Am. Chem. SOC.1992. 114, 5579-5584.
[ l l ] B. M. Trost, R. J. Kulawiec, J. A m . Chem. Soc. 1993, 115, 2027-2036.
[12] B. M. Trost, J. A. Martinez, R. J. Kulawiec. A. F. Indolese, J. A m . Chem. Soc.,
in press.
1131 T. Mitsudo. H. Naruse, T. Kondo, Y Ozdki, Y Watanabe, Angeit. Chem. 1994,
106. 595-597: A n g e u . Chem. Int. Ed. Engl. 1994, 33, 580-581.
[14] N.Oshima, H. Suzuki. Y. Moro-oka, Chem. Leu. 1984, 1161-1164.
1151 T. Mitsudo, K. Kokuryo. T. Shinsugi. Y. Nakagawa, Y. Watanabe. Y.
Takegami. J. Orx. Chem. 1979. 44, 4492-4496.
[16] T. Mitsudo, Y. Hori, Y. Watanahe, J. Organomer. Chem. 1987, 334, 157-167.
1171 P. G . Gassmdn. J. W. Mickelson. J. R. Sowa, Jr., J. A m . Chem. So(. 1992, 114.
6942 -6944.
1181 M. A. Halcrow. F. Urbanos, B. Chaudret. Organomerullics 1993. 12. 955957.
0570-O833194/0606-0638S 10 OOf 25 0
Angeii Chem Inr Ed Engl 1994, 33, No 6
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framework, reaction, reagents, metali, construction, cyclooctadiene, transitional, complexes, ruthenium, carbon, help, catalyzed
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