3
A second portion of product 21 was treated with allene 14 after
the metathesis reaction was complete and stirred at room
temperature for an hour before purifying using the same flash
chromatography conditions.15 A UV/Vis analysis suggests that
quenching with allene ester removed the majority of Ruthenium
impurities (Scheme 4, Ru absorbance at 376 nm was not
observed).
Supplementary data
Supplementary data
(general
experimental
details,
characterization data of all products, H and 13C NMR spectra of
representative products) associated with this article can be found,
in the online version, at…
1
References and notes
In summary, our studies suggest that allenyl esters do not
undergo olefin metathesis with traditional ruthenium catalysts.
Instead, these allenes esters completely inhibit metathesis
activity. The organometallic complex that forms between
ruthenium catalyst and allenyl esters is conveniently removed
using standard silica chromatography. This use of simple allenyl
esters offers a useful alternative to traditional quenching agents
for the removal of Ru impurities.
1. (a) Roy, A.; Bhat, B. A.; Lepore, S. D. Org. Lett. 2016, 18, 1230; (b) Roy,
A.; Bhat, B. A.; Lepore, S. D. Org. Lett. 2015, 17, 900.
2. (a) Maity, P.; Lepore, S. D. J. Am. Chem. Soc. 2009, 131, 4196; (b)
Silvestri, M. A.; Bromfield, D. C.; Lepore, S. D. J. Org. Chem. 2005, 70,
8239.
3. However, two reports indicate that aliphatic allenes undergo homo-
metathesis in the presence of ruthenium catalysts: (a) Ahmed, M.;
Arnauld, T.; Barrett, A. G. M.; Braddock, C. D.; Flack, K.; Procopiou, P.
A. Org. Lett. 2000, 2, 551; (b) Janben, C. E.; Krause, N. Eur. J. Org.
Chem. 2005, 2322.
4. The chromatography profile and spectroscopic characterization of this
waxy solid using 1H, 13C NMR, and MS (MALDI TOF) argue for an
oligomeric compound: 1H NMR (400 MHz, CDCl3) 5.82 (s, 1H), 4.07
(q, 2H, J = 7.2 Hz), 3.51 (s, 2H), 1.22 (t, 3H, 7.2 Hz); 13C NMR (100
MHz, CDCl3) 165.7, 154.2, 119.6, 59.7, 39.9, 14.1; MS (MALDI TOF)
393.4613 (base), 407.4503, 519.5390, 631.6328, 742.7199. These last
few peaks are 112 m/z units apart which is the mass of allene 5.
5. Lipshutz, B. H.; Aguinaldo, G. T.; Ghorai, S.; Voigtritter, K. Org. Lett.
2008, 10, 1325.
6. For vinylidene complexes please see (a) Bruce, M. I. Chem.
Rev. 1991, 91, 197; (b) Bruneau, C.; Dixneuf, P. H. Acc. Chem. Res. 1999,
32, 311; (c) Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem.
Soc. 1996, 118, 100; (d) Lynam, J. M. Chem. Eur. J. 2010, 16, 8238. For
allenylidene complex: R. Castarlenas, C. Fischmeister, C. Bruneau, P. H.
Dixneuf, J. Mol. Catal. A: Chem. 2004, 213, 31.
(b)
7. We noticed that one equivalent of allene ester leads to the dissociation of
styrene isopropoxy ligand from ruthenium catalyst 4 suggesting the initial
formation of a Ru vinylidene species. However, we did not observe
characteristic peaks for Ru=C(H), Ru=C, or Ru=C=C (see Supplementary
data): R os saa e Los; Bustelo, E.; Puerta, M. C.; Valerga, P.
Organometallics 2010, 29, 1740.
8. Maynard, H. D.; Grubbs, R. H. Tetrahedron Lett. 1999, 40, 4137.
9. For a review see: Clavier, H.; Grela, K.; Kirschning, A. M.; Nolan, S. P.
Angew. Chem. Int. Ed. 2007, 46, 6786.
For more recent strategies see: (a) Hobbs, C.; Yang, Y.; Ling, J.; Nicola,
S.; Su, H.; Bazzi, H. S.; Bergbreiter, D. E. Org. Lett. 2011, 13, 3904; (b)
Allen, D. P.; Van Wingerden, M. M.; Grubbs, R. H. Org. Lett. 2009, 11,
1261.
10. Rosen, E. L.; Varnado, C. D.; Arumugam, K.; Bielawski, C. W. J.
Organomet. Chem. 2013, 201, 745.
11. Schachner, J. A.; Cabrera, J.; Padilla, R.; Fischer, C.; Van der Schaaf, P.
A.; Pretot, R.; Rominger, F.; Limbach, M. ACS Catal. 2011, 1, 872; (b) J.
Cabrera, R. Padilla, R. ehn, S. euerlein,Ł. Gułajski, E. Chomisz zak,
J.H. Teles, M. Limbach, K. Grela, Adv. Synth. Catal. 2012, 354, 1043.
12. French, J. M.; Caras, C. A.; Diver, S. T. Org. Lett. 2013, 15, 5416.
13. Others have reported
a strong Ru absorbance (ε= 7000−20,000
Scheme 4. (a) Various purification schemes for product 21; (b)
Comparison of Ru content by UV/Vis spectra (in toluene); (I)
Catalyst 4, (II) product 21 after simple silica gel flash
chromatography and (III) 21 was treated with allene 14 followed
by flash chromatography.
L·mol−1·cm−1) at 376 nm, which are likely due to metal-to-ligand charge
transfer (MLCT) into the π* orbital of the Ru=CHR, Please see Table 2
and S32 (supporting information) of Thiel, V.; Hendann, M.; Wannowius,
K.; Plenio, H. J. Am. Chem. Soc. 2012, 134, 1104.
14. Ethyl vinyl ether (EVE) is known to arrest metathesis activity after asingle
cycle and used to quench ruthenium carbene catalysts. Excess EVE (~100
equiv. relative to catalyst) was added to quench any metathesis active
species. It forms stable complex with Ru carbene: (a) Nagarkar, A. A.;
Kilbinger, A. F. M. Nature Chem. 2015, 7, 718; (b) Wu, Z.; Nguyen, S.
T.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1995, 117, 5503.
Acknowledgments
15. Representative procedure
- metathesis of 20 followed by allene
This work was supported by a grant from the National Institutes
of Health (GM110651). We thank Prof. Deguo Du and Haiyang
(Ocean) Liu for their help in acquiring UV/Vis spectra.
quenching: (Please see Supplementary Data for additional detail) After
the metathesis reaction was complete, the heating bath was removed and
the reaction mixture was allowed to cool for 5 min. Allene ester 14 (~100
equiv. relative to catalyst) was added as a DCM solution to arrest any