IR-Thermographic Screening of Thermoneutral or Endothermic Transformations: The Ring-Closing Olefin Metathesis Reaction

Full text of DOI:10.1002/(SICI)1521-3773(20000403)39:7<1236::AID-ANIE1236>3.0.CO;2-J

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[
4] a) A. Fürstner, G. Seidel, Angew. Chem. 1998, 110, 1758 ± 1760;
Angew. Chem. Int. Ed. 1998, 37, 1734 ± 1736. b) A. Fürstner, O. Guth,
A. Rumbo, G. Seidel, J. Am. Chem. Soc. 1999, 121, 11108 ± 11113.
5] a) R. R. Schrock, D. N. Clark, J. Sancho, J. H. Wengrovius, S. M.
Rocklage, S. F. Pedersen, Organometallics 1982, 1, 1645 ± 1651; b) J. H.
Freudenberger, R. R. Schrock, M. R. Churchill, A. L. Rheingold, J. W.
Ziller, Organometallics 1984, 3, 1563 ± 1573; c) R. R. Schrock, Poly-
hedron 1995, 14, 3177 ± 3195.
55 (21); HRMS (C26
42 4
H O Si): m/z: 446.2850 (calcd: 446.2852);
elemental analysis (%) calcd for C26
9.48; found: C 70.08, H 9.42.
42 4
H O Si (446.71): C 69.91, H
[
[19] R. F. Newton, D. P. Reynolds, C. F. Webb, S. M. Roberts, J. Chem. Soc.
Perkin Trans. 1 1981, 2055 ± 2058.
[20] We consider the ªeconomy of stepsº as a strategic goal for target
oriented syntheses in general, see: A. Fürstner, Synlett 1999, 1523 ±
1533.
[
[
6] A. Fürstner, C. Mathes, C. W. Lehmann, J. Am. Chem. Soc. 1999, 121,
[21] Compound 1: colorless needles; mp 76.5 ± 77.58C (Et
2
O/pentane)
);
O/hexane)]; [a]2
0
ˆ � 185.0 (0.15, CHCl
9
453 ± 9454.
7] For a review on preparation and coordination chemistry of [Mo-
N(tBu)(Ar)} ] see: C. C. Cummins, Chem. Commun. 1998, 1777 ±
786.
[ref [10c] 73 ± 768 (Et
H NMR (600 MHz, CDCl
2
D
3
1
3
): d ˆ 0.89 (3H, t, J ˆ 6.8 Hz), 1.20 ± 2.18
{
3
(16H, m), 2.20 (1H, ddd, J ˆ 13.2, 9.4, 3.3 Hz), 2.21 (1H, dd, J ˆ 18.9,
9.3 Hz), 2.29 (1H, dt, J ˆ 13.2, 8.8 Hz), 2.40 (1H, ddd, J ˆ 13.3, 8.7,
3.2 Hz), 2.80 (1H, ddd, J ˆ 18.8, 7.8, 1.2 Hz), 4.14 (1H, dt, J ˆ 7.9,
9.2 Hz), 5.20 (1H, dt, J ˆ 8.5, 6.0 Hz), 5.35 (1H, ddd, J ˆ 10.4, 9.6,
5.5 Hz), 5.60 (1H, dt, J ˆ 10.5, 5.9 Hz), 5.81 (1H, dd, J ˆ 15.9, 8.7 Hz),
1
[
8] For a short review on alkyne metathesis see: U. H. F. Bunz, L.
Kloppenburg, Angew. Chem. 1999, 111, 503 ± 505; Angew. Chem. Int.
Ed. 1999, 38, 478 ± 481.
9] a) C. Cimino, A. Crispino, V. Di Marzo, G. Sodano, A. Spinella, G.
Villani, Experientia 1991, 47, 56 ± 60; b) G. Cimino, A. Spinella, G.
Sodano, Tetrahedron Lett. 1989, 30, 3589 ± 3592; c) G. Cimino, A.
Crispino, V. Di Marzo, A. Spinella, G. Sodano, J. Org. Chem. 1991, 56,
13
[
6.11 (1H, dd, J ˆ 15.8, 6.6 Hz); C NMR (150 MHz, CDCl ): d ˆ 14.0,
3
22.5, 23.9, 25.3, 25.5, 25.6, 31.5, 34.0, 34.2, 45.5, 55.0, 57.9, 71.7, 71.8,
128.9, 129.3, 131.9, 134.7, 173.2, 213.1. IR (Kbr): nÄ ˆ 3431, 3002, 2938,
�
1
‡
2857, 1726, 1377, 1243, 1160, 1041, 728 cm . MS (EI): m/z: 334 ([M ],
24), 316 (38), 298 (13), 262 (39), 208 (63), 163 (64), 151 (22), 145
(15),133 (25), 121 (28), 107 (42), 91 (78), 79 (100), 67 (83), 55 (93).
[22] For a study on the solid phase synthesis of prostaglandin derivatives
and of small prostaglandin libraries see: a) L. A. Thompson, F. L.
Moore, Y. C. Moon, J. A. Ellman, J. Org. Chem. 1998, 63, 2066 ± 2067;
b) D. R. Dragoli, L. A. Thompson, J. OꢁBrien, J. A. Ellman, J. Comb.
Chem. 1999, 1, 534 ± 539; c) K. J. Lee, A. Angulo, P. Ghazal, K. D.
Janda, Org. Lett. 1999, 1, 1859 ± 1862.
2907 ± 2911.
[
10] Compound 1 and other prostaglandin lactones have previously been
prepared by conventional macrolactonization of the parent prosta-
glandins, see: a) E. J. Corey, K. C. Nicolaou, L. S. Melvin, J. Am.
Chem. Soc. 1975, 97, 653 ± 654; b) K. Narasaka, K. Maruyama, T.
Mukaiyama, Chem. Lett. 1978, 885 ± 888; c) G. C. Bundy, D. C.
Peterson, J. C. Cornette, W. L. Miller, C. H. Spilman, J. W. Wilks, J.
Med. Chem. 1983, 26, 1089 ± 1099; d) G. D. Bundy, D. R. Morton, D. C.
Peterson, E. E. Nishizawa, W. L. Miller, J. Med. Chem. 1983, 26, 790 ±
799.
[
11] For timely and comprehensive treatises see: a) Prostaglandins,
Leucotrienes and Other Eicosanoids. From Biogenesis to Clinical
Applications (Eds.: F. Marks, G. Fürstenberger), WILEY-VCH,
Weinheim, 1999; b) P. W. Collins, S. W. Djuric, Chem. Rev. 1993, 93,
1533 ± 1564.
[
12] For reviews on ªthree-component couplingº see: a) R. Noyori, M.
Suzuki, Angew. Chem. 1984, 96, 854 ± 882; Angew. Chem. Int. Ed.
Engl. 1984, 23, 847; b) R. Noyori, Asymmetric Catalysis in Organic
Synthesis, Wiley, New York, 1994, pp. 298 ± 322.
IR-Thermographic Screening of Thermoneutral
or Endothermic Transformations: The Ring-
Closing Olefin Metathesis Reaction
[
13] S-M. L. Chen, R. E. Schaub, C. V. Grundziskas, J. Org. Chem. 1978,
4
3, 3450 ± 3454. This paper pretends that the hydrostannylation of the
Manfred T. Reetz,* Michael H. Becker, Monika Liebl,
and Alois Fürstner
TES ether of alcohol 5 is regio- and diastereoselective according to
13
C NMR data. Careful analysis of the crude product by HPLC,
however, shows that the purity is only about 90%. This material can
be used directly in the next step, because the isomeric by-products do
not undergo productive 1,4-addition, see: C. R. Johnson, T. D.
Penning, J. Am. Chem. Soc. 1988, 110, 4726 ± 4735.
Whereas combinatorial chemistry in the area of pharma-
ceutical research has reached maturity,[ the use of appro-
priate systems in catalysis still poses challenges. Recently we
1]
[2]
[
[
14] a) For the preparation of enone 7 see: R. Noyori, I. Tomino, M.
Yamada, M. Nishizawa, J. Am. Chem. Soc. 1984, 106, 6717 ± 6725;
b) C. J. Forsyth, J. Clardy, J. Am. Chem. Soc. 1990, 112, 3497 ±
reported the first cases of IR-thermographic detection and
parallel screening of enantioselectivity in transition metal
catalyzed and biocatalyzed organic transformations.[ The
test reactions chosen were all exothermic processes, enantio-
selectivity showing up as ªhot spotsº in the respective IR-
thermographic images. IR-thermography had previously been
used as a detection and/or screening system in achiral
exothermic reactions mediated by heterogeneous catalysts.[
3]
3
505.
15] a) Iodide 9 was prepared by treatment of commercially available
-butyn-1-ol with PPh , I , and imidazole according to a literature
procedure: G. L. Lange, C. Gottardo, Synth. Commun. 1990, 20,
2
3
2
1
3
473 ± 1479; b) acid 12 was prepared from commercially available
-pentyn-1-ol as described in: M. F. Ansell, J. C. Emmet, R. V.
4]
Coombs, J. Chem. Soc. C 1968, 217 ± 225.
[
[
[
16] The three-component coupling was essentially carried out as descri-
bed in: M. Suzuki, Y. Morita, H. Koyano, M. Koga, R. Noyori,
Tetrahedron 1990, 46, 4809 ± 4822.
Indeed, it was quietly assumed that only exothermic processes
[2, 4, 5]
can be assayed by this method.
We now report that
exothermicity is not a requirement in IR-thermographic
screening of catalysts. Specifically, we demonstrate for the
first time that in appropriate systems endothermic or even
thermoneutral reactions can be successfully screened by time-
17] a) Determined by HPLC on a Chiracel OD-H column with n-heptane/
2-propanol as mobile phase. b) Determined by HPLC on a Chiralpak
AD column with n-heptane/2-propanol (95:5) as mobile phase.
2
0
18] Compound 14: colorless syrup; [a]
D
ˆ � 189.7 (c ˆ 0.23, CHCl
3
);
1
H NMR (300 MHz, CDCl
3
): d ˆ 0.03 (3H, s), 0.04 (3H, s), 0.87 (9H,
s), 1.20 ± 2.50 (21H, m), 2.69 (1H, dd, J ˆ 18.4, 7.8 Hz), 2.98 (1H, d, J ˆ
1
5.4 Hz), 4.0 (1H, m), 5.10 (1H, dt, J ˆ 8.0, 5.2 Hz), 5.88 (2H, m);
[*] Prof. Dr. M. T. Reetz, Dipl.-Chem. M. H. Becker,
Dipl.-Chem. M. Liebl, Prof. Dr. A. Fürstner
Max-Planck-Institut für Kohlenforschung
Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr (Germany)
Fax : (‡ 49)208-306-2985
13
C NMR (75 MHz, CDCl
3
): d ˆ � 4.8, � 4.6, 14.0, 17.5, 18.0, 19.0, 22.5,
2
1
1
3
2.6, 25.5, 25.7, 31.6, 34.1, 34.9, 46.6, 54.8, 56.1, 72.2, 73.0, 79.3, 79.6,
30.4, 132.3, 172.4, 211.8; IR (neat): nÄ ˆ 2955, 2930, 2857, 1746, 1252,
�
1
‡
154, 1115, 964, 839, 778 cm ; MS (EI): m/z: 446 ([M ], 1), 431 (1),
89 (33), 317 (18), 297 (8), 225 (5), 155 (5), 129 (10), 91(12), 75 (100),
E-mail: reetz@mpi-muelheim.mpg.de
1236
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Angew. Chem. Int. Ed. 2000, 39, No. 7

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resolved detection of ªcold spotsº in IR-thermographic
images.
We chose the well-known Ru-catalyzed ring-closing olefin
[
6]
metathesis (RCM) as the reaction to be scrutinized IR-
thermographically, not knowing at the outset whether this is
actually an exo- or endothermic process. In an exploratory
study using the same instrument and method as previously
[
3, 4a]
[6]
described,
the known reaction of 1,7-octadiene (5) with
formation of cyclohexene (6) and ethylene (7) was carried out
at 328C on a 24-well microtiter plate employing the conven-
tional Grubbs precatalysts 1 and 2 and the more recently
[
7]
developed complexes 3 and 4.
Figure 1. Time-resolved IR-thermographic imaging of the Ru-catalyzed
RCM reaction of diene 5.
studying lab-scale reactions of diene 5 with precatalysts 1 ± 4.
Indeed, complete correspondence was observed. Thus, it was
found that under standard conditions the reactions catalyzed
by 1 ± 3 are essentially over within 1 min at 258C, whereas the
reaction catalyzed by 4 requires 10 min for complete con-
version under otherwise identical conditions.
Unfortunately, thermodynamic data for the reaction
5
!6 ‡ 7 are not available. However, application of the
ASPIN program for calculating thermodynamic data predicts
�
1
a heat of reaction (reaction enthalpy) of 4.8 kJmol , indicat-
ing that the reaction of interest should be slightly endothermic
or nearly thermoneutral.[ Thus the present data can be
interpreted on the basis of slight endothermicity, differences
in the IR-thermographic images being due to differences in
catalyst activity. However, it is not clear how much of the
liberated ethylene (6) actually evaporates from the solutions,
a process that would also lead to ªcold spotsº. It is likely that
at least some of the effects seen in the IR-thermographic
images are in fact due to the heat of vaporization of ethylene
from the reaction mixture.[ Indeed, upon gently blowing
ethylene through a toluene-containing well on the microtiter
plate comparable to the bubbling observed during an actual
reaction, a ªcold spotº immediately became visible. For the
purpose of screening, the relative importance of the origins of
the ªcold spotsº is not decisive. It is the sum of the two
effects in the overall process which comprises the detection
system.
9]
Four wells of the microtiter plate were charged with a
solution of 5 in toluene (wells 1 ± 4), the fifth one (well C)
containing octane in place of 5 as a control. Once the
temperature was thermostatically set at 328C, 250 IR-thermo-
graphic pictures were taken within 5 s, the average of which is
10]
[
8]
shown in Figure 1a. The solutions in wells 1 ± 4 were then
treated with precatalysts 1 ± 4, respectively. Precatalyst 1 was
also added to the control well C. After one minute, shaking
was interrupted and the IR-thermographic pictures were
taken (average of 250 recordings), resulting in the image
shown in Figure 1b. Shaking was then resumed and the
process repeated after one more minute (Figure 1c). Using
the temperature/color key of the temperature window (bar on
far right), several remarkable features immediately become
apparent. Whereas the emissivities of wells C and 4 remain
approximately constant, those of wells 1 ± 3 clearly reveal
ªcold spotsº, implying heat uptake. This shows that the RCM
of 5 leads to an endothermic effect on the microtiter plate,
suggesting that the Grubbs precatalyst 1 as well as complexes
According to the mechanistic work of Grubbs et al.
concerning RCM,[ compounds 1 and 2 are precatalysts.
Following initial [2‡2] cycloaddition of the ruthenium ± car-
bene complex with an olefinic function, the primary metal-
locyclobutane undergoes cycloreversion with formation of a
new carbene complex which then adds intramolecularly to the
second olefin function. The final step is cycloreversion with
formation of the cyclic olefin (e.g., 6), ethylene (7), and yet
another carbene complex [L RuˆCH ], which then mediates
11]
n
2
11]
2
and 3 are considerably more active than precatalyst 4. Close
more than 95% of the reaction.[ It is therefore clear that
ªcatalyst activityº as observed in the present IR-thermo-
graphic study or in conventional detection of lab-scale
reactions reflects the ease of initiation of RCM by the
inspection of the emissivities of wells 1 ± 3 in Figure 1c leads
to the qualitative conclusion that precatalyst 2 is somewhat
less active than 1 or 3. These conjectures were tested by
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carbene complexes 1 ± 4. Stated in different terms, it simply
means that in the present study most or all of the precatalyst 1
or 3 has been consumed within the first two minutes, allowing
the reaction of [L RuˆCH ] to proceed. In contrast, a
n
2
considerable (or major) portion of the less reactive complexes
2
or 4 did not react at all under the same conditions.
We then proceeded to screen the reaction of other
substrates 8a ± 8e by employing the same set of precatalysts
[
12]
1
± 4. By using a modified setup, the wells of a polypropylene
microtiter plate were filled row by row with substrates 8a ± 8e
EtO C CO Et
EtO2C
CO Et
2
2
2
3
0 °C
n
n
cat. 1 - 4
8
8
8
a, n = 1
b, n = 2
c, n = 3
9 a, n = 1
9 b, n = 2
9 c, n = 3
EtO C CO Et
EtO2C
CO Et
2
2
2
30 °C
cat. 1 - 4
Figure 2. Time-resolved IR-thermographic imaging of the Ru-catalyzed
RCM reaction of dienes 8a ± 8e with precatalysts 1 ± 4.
8d
9d
comparison should not be made. In these experiments
complex 4 seems to be the most active catalyst. However,
caution must be exercised because the results suggested by the
IR-thermographic images are in fact due to the delay
associated with the row-wise addition of catalysts. In reality
the major part of dienes 8d and 8e has been converted to the
cyclic products 9d and 9e by the time the first thermographic
image is taken, conversion then being in the phase of leveling
off. Precatalyst 4 is actually considerably less active than
complexes 1 ± 3, the system reaching maximum activity only
after about 10 min (Figure 2d). At this time the reactions of
substrates 8d and 8e catalyzed by 1 ± 3 are almost over. When
the order of catalyst addition to the wells on the microtiter
plate was reversed starting with 8a and ending with 8e, heat
uptake turned out to be more pronounced in reactions of
substrates 8d and 8e catalyzed by complexes 1 ± 3 (images not
shown). The reactions of the more reactive substrates had
proceeded to such an extent that no significant heat uptake
was actually detectable at the time of recording. These
observations show that two sets of experiments are necessary
for correct conclusions (unless of course the precatalysts were
to be added simultaneously to all wells with an appropriate
multichannel pipette robot). Our conclusions concerning
ªcatalyst activityº were fully corroborated by lab-scale kinetic
studies of the reaction of diene 8e catalyzed by complexes 1 ±
4 (Figure 3). It is clear that precatalyst 4 is least active.
EtO C CO Et
EtO2C
CO Et
2
2
2
3
0 °C
cat. 1 - 4
8e
9e
according to the arrangement shown in Figure 2a. After
calibration the precatalysts were added simultaneously with
an Eppendorf multipipette to the wells of one specific diene,
starting with the least reactive substrate 8e and ending with
the most reactive substrate 8a. All additions were completed
within 90 s. Figure 2 summarizes the time-resolved IR-ther-
mographic screening of these reactions.
Again, several noteworthy features become visible. The
substrates 8a and 8b are by far the most active ones yielding
the five- and six-membered cyclic olefins 9a and 9b,
respectively. As before, precatalysts 1 ± 3 are considerably
more active than 4. Especially the reaction of precatalyst 1
with 8a and 8b is essentially complete within 2 min, which was
also demonstrated in additional experiments of 1 and 3 with
these substrates on a shorter time scale. Figure 2 also shows
that the reaction of 8c with precatalysts 1 ± 4, leading to the
seven-membered product 9c is considerably slower. The rate
of RCM as indicated by heat uptake is lowest in the case of
diene 8e having an internal olefinic double bond. This
corresponds to the results of lab-scale reactions. This also
appears to be the case in the reaction of substrate 8d which
likewise contains a disubstituted olefinic function. However,
since propylene rather than ethylene is liberated, direct
We have devised an efficient screening system for catalytic
reactions based on IR-thermography in which high catalyst
activity is identified by heat uptake from the surroundings as
monitored by the appearance of ªcold spotsº. The heat of
vaporization of one of the (gaseous) reaction products
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thus formed was a ruthenium allenylidene species, cf. K. J. Harlow,
A. F. Hill, J. D. E. T. Wilton-Ely, J. Chem. Soc. Dalton Trans. 1999,
Figure 3. Kinetics of the RCM reaction of 8e catalyzed by the Ru
complexes 1 ± 4.
2
85 ± 292. More detailed studies, however, have shown that the stable
product formed in this reaction is the rearranged compound, that is
the indenylidene ruthenium complex 3; the same applies to the
synthesis of 4. Cf. A. F. Hill, A. Fürstner, M. Liebl, R. Mynott, B.
Gabor, L. Jafarpour, S. P. Nolan, unpublished results.
(
ethylene or propylene) plays a pivotal role.[10] These findings
add a new dimension to the evolving area of high-throughput
catalyst or reagent screening based on IR-thermography.[2±4]
[8] To prevent uncontrolled evaporation of solvent, screening was
performed in a closed fume hood without ventilation.
9] We thank Dr. P. Schwab and Dr. G. Kautz (BASF AG, Ludwigshafen)
Moreover, this study shows that IR-thermography constitutes
a simple way to assess the relative rate of initiation of RCM
events by different precatalysts as well as the inherent
reactivity of variously substituted diene substrates towards
the reaction. Therefore the method will greatly facilitate
[
for this calculation.
[
[
[
10] Strictly speaking one also has to consider various other enthalpies (i.e.
enthalpy of mixing, enthalpy of solvation) which contribute to the
effects seen in the thermographic images.
11] a) E. L. Dias, S. T. Nguyen, R. H. Grubbs, J. Am. Chem. Soc. 1997, 119,
[
6]
further investigations in this timely field of research.
3
1
887 ± 3897; b) O. M. Aagaard, R. J. Meier, F. Buda, J. Am. Chem. Soc.
998, 120, 7174 ± 7182.
Received: November 17, 1999 [Z14288]
12] For the substrate/catalyst activity screening the substrates were placed
in the wells of a 96-well polypropylene microtiter plate (100 mL
substrate per well). The temperature was calibrated in the range of
25 ± 358C. The reaction was initiated by the simultaneous addition of
100 mL of the four different precatalyst solutions (1 ± 4) in toluene
(0.01m corresponding to 0.26 mol% precatalyst) at 308C to each
substrate using a multiple pipette (the addition of the precatalyst
solutions was completed within 90 s). As before, the temperature
changes were detected periodically, shaking being interrupted. The
detection time was 5 s, resulting in 250 recordings which were
averaged.
[
1] a) F. Balkenhohl, C. von dem Bussche-Hünnefeld, A. Lansky, C.
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[
[
[
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Host within a Host: Encapsulation of Alkali
Ion ± Crown Ether Complexes into a [Ga L ]
1
12�
Taylor, J. P. Morken, Science 1998, 280, 267 ± 270; c) G. Georgiades,
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DꢁNetto, L. F. Razon, J. R. Brown in Chemical Instabilities (Eds.: G.
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4
6
Supramolecular Cluster**
Tatjana N. Parac, Markus Scherer, and
Kenneth N. Raymond*
We have constructed structures based on supramolecular
clusters found in nature and shown that they encapsulate
[1]
molecular cations. The origins of supramolecular chemistry
[
*] Prof. Dr. K. N. Raymond, Dr. T. N. Parac, Dr. M. Scherer
Department of Chemistry
University of California
Berkeley, CA 94720, (USA)
[
[
5] A. H. Hoveyda, Chem. Biol. 1998, 5, R187 ± R191.
6] For recent reviews on RCM: a) R. H. Grubbs, S. Chang, Tetrahedron
1998, 54, 4413 ± 4450; b) A. Fürstner, Top. Organomet. Chem. 1998, 1,
37 ± 72; c) A. Fürstner, Top. Catal. 1998, 4, 285 ± 299; d) M. Schuster, S.
Fax:(‡1)510-486-1460
Blechert, Angew. Chem. 1997, 109, 2125 ± 2144; Angew. Chem. Int. Ed.
Engl. 1997, 36, 2036 ± 2055; e) for enantioselective developments see:
A. H. Hoveyda, Top. Organomet. Chem. 1998, 1, 105 ± 132; f) for a
review on RCM by complexes of molybdenum and tungsten: R. R.
Schrock, Top. Organomet. Chem. 1998, 1, 1 ± 36.
E-mail: raymond@socrates.berkeley.edu
[**] Coordination Number Incommensurate Cluster Formation, Part 13.
This research was supported by NSF grant CHE-9709621 and by
exchange grants NSF INT-9603212 and NATO SRG951516. We thank
the Alexander von Humboldt Foundation for a fellowship to M.S.
Part 12: D. W. Johnson, J. Xu, R. W. Saalfrank, K. N. Raymond,
Angew. Chem. 1999, 111, 3058 ± 3061; Angew Chem. Int. Ed. 1999, 38,
2882 ± 2885.
[
7] a) A. Fürstner, A. F. Hill, M. Liebl, J. D. E. T. Wilton-Ely, Chem.
Commun. 1999, 601 ± 602. b) Complex 3 is formed by reaction of
[
(PPh
3
)
3
RuCl
2
] and HCꢀCCPh
2
OH followed by substitution of the
. Originally, it was believed that the complex
PPh ligands with PCy
3
3
Angew. Chem. Int. Ed. 2000, 39, No. 7
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