Organic Letters
Letter
(7) (a) Kim, K. S. WO 2014011712. (b) Nair, A. G.; Keertikar, K. M.;
Kim, S. H.; Kozlowski, J. A.; Rosenblum, S.; Selyutin, O. B.; Wong, M.;
Yu, W.; Zeng, Q. WO 2011112429.
(8) Blizzard, T. A.; Chobanian, H.; Greenlee, W.; Singh, S. WO
2014058538 A1 20140417.
di-tert-butyl-4-methoxyphenol. The concentration of 9 in this solution
was unchanged for at least 5 months after multiple 5−25 °C cool−heat
cycles. (b) Levy, L. B. Process Saf. Prog. 1993, 12, 47−48.
(21) Silane 10 is commerically available or could be easily prepared
from the readily available chloro(chloromethyl)dimethylsilane Tacke,
R. J. Organomet. Chem. 1990, 388, 57−62.
(9) (a) Shimizu, H.; Nagasaki, I.; Sayo, N.; Saito, T. In Asymmetric
Synthesis and Application of α-Amino Acids; Soloshonok, V. A., Izawa,
K., Eds.; ACS Symposium Series 1009; American Chemical Society:
Washington, DC, 2009; Chapter 13; pp 203−226. (b) Kreuzfeld, H. J.;
(22) Dolman, S. J.; Nyrop, J. L.; Kuethe, J. T. J. Org. Chem. 2011, 76,
993−996.
(23) Possible reaction pathways are depicted below; L may be
solvent, NBD, or a coordinating group on the substrate in analogy to
rhodium-catalyzed asymmetric hydrogenation. After oxidative addition
8 + 15 → 16, the catalytic cycle may proceed via insertion of either Si
or H into either the α- or β-carbon of the olefin. The desired product
is formed in the case of β-Si insertion and reductive elimination 16 →
17 → 15 + 8 and in the case of α-H insertion and reductive
elimination 16 → 18 → 15 + 8. The process of β-H insertion 16 → 19
may occur; however, subsequent reductive elimination 19 → 15 + 20
is unlikely due to the ring strain of 20 and was never observed
experimentally. Since all steps in catalytic hydrosilylation prior to
reductive elimination are believed to be reversible, any 19 formed will
equilibrate back to 16 and eventually form product. Similarly, the α-Si
insertion 16 → 21 is also precluded by ring strain. For these reasons,
tethering the silane to the alkene prevents the 1,4-reduction observed
in intermolecular reactions.
Dobler, C.; Schmidt, U.; Krause, H. W. Amino Acids 1996, 11, 269−
̈
282. (c) Bommaris, A. S.; Schwarm, M.; Drauz, K. Chimia 2001, 55,
50−59. (d) Breuer, M.; Ditrich, K.; Habicher, T.; Hauer, B.; Keβeler,
M.; Sturmer, R.; Zelinski, T. Angew. Chem., Int. Ed. 2004, 43, 788−824.
̈
́
(e) Najera, C.; Sansano, J. M. Chem. Rev. 2007, 107, 4584−4671.
(10) (a) Chen, J.; Cao, M.; Cheng, B.; Lu, Z. Synlett 2015, 26, 2332−
2335. (b) Hua, Y.; Nguyen, H. H.; Trog, G.; Berlin, A. S.; Jeon, J. Eur.
J. Org. Chem. 2014, 2014, 5890−5895. (c) Hua, Y.; Nguyen, H. H.;
Scaggs, W. R.; Jeon, J. Org. Lett. 2013, 15, 3412−3415. (d) Alavi, S.;
Huchet, Q.; Vacher, B. Tetrahedron 2011, 67, 7598−7602. (e) Bo, Y.;
Singh, S.; Duong, H. Q.; Cao, C.; Sieburth, S. M. Org. Lett. 2011, 13,
1787−1789.
(11) (a) Our initial investigations of the intermolecular hydro-
silylation employed conditions similar to those for the intramolecular
screens described in the text and found very low reactivity even at 10%
catalyst loading and 60 °C, affording mostly unreacted starting
materials along with minor 1,4-reduction product. (b) After
completion of this work, G. Persanti et al. reported a racemic
synthesis of silicon-containing amino acids through copper-catalyzed
conjugate additions to dehydroalanine derivatives: Bartoccini, F.;
Bartolucci, S.; Lucarini, S.; Piersanti, G. Eur. J. Org. Chem. 2015, 2015,
3352−3360.
(12) Though the intramolecular hydrosilylation of simple alkenes
with tethered alkoxysilane to access 1,3-diols have been known since
1996, the use of this reaction to directly set amine stereocenters is
without precedent. (a) Tamao, K.; Tohma, T.; Inui, N.; Nakayama, O.;
Ito, Y. Tetrahedron Lett. 1990, 31, 7333−7336. (b) Bergens, S. H.;
Noheda, P.; Whelan, J.; Bosnich, B. J. Am. Chem. Soc. 1992, 114,
2121−2128. (c) Wang, X.; Bosnich, B. Organometallics 1994, 13,
4131−4133. (d) Barnhart, R. W.; Wang, X.; Noheda, P.; Bergens, S.
H.; Whelan, J.; Bosnich, B. Tetrahedron 1994, 50, 4335−4346.
(13) Shimizu, H.; Saito, T.; Nagasaki, I. EP 1419815A1, 2004.
(14) Xiao, D.; Zhang, X. Angew. Chem., Int. Ed. 2001, 40, 3425−3428.
(15) Blaser, H.-U.; Brieden, W.; Pugin, B.; Spindler, F.; Studer, M.;
Togni, A. Top. Catal. 2002, 19, 3−16.
(16) Yu, M.; Jing, H.; Fu, X. Inorg. Chem. 2013, 52, 10741−10743.
(17) The 24 solvents were DCE, CH2Cl2, PhCF3, PhCl, THF,
CPME, MTBE, DME, 2-Me-THF, PhOMe, dioxane, EtOAc, iPrOAc,
acetone, toluene, heptane, MeCN, DMA, DMSO, MeNO2, MeOH,
iPrOH, tAmOH, and TFE.
(18) One explanation for increasing reactivity with decreasing catalyst
concentration is that the active catalyst species may be in equilibrium
with an inactive dimer. For selected recent examples of this
phenomenon in transition metal catalysis, see: (a) Hruszkewycz, D.
P.; Balcells, D.; Guard, L. M.; Hazari, N.; Tilset, M. J. Am. Chem. Soc.
2014, 136, 7300−7316. (b) Dervisi, A.; Carcedo, C.; Ooi, L.-L. Adv.
Synth. Catal. 2006, 348, 175−183. (c) Kina, A.; Iwamura, H.; Hayashi,
T. J. Am. Chem. Soc. 2006, 128, 3904−3905. (d) Tromp, M.; Sietsma,
J. R. A.; van Bohkoven, J. A.; van Strijdonck, G. P. F.; van Haaren, R. J.;
van der Eerden, A. M. J.; van Leeuwen, P. W. N. M.; Koningsberger,
D. C. Chem. Commun. 2003, 128−129. (e) Pohlki, F.; Doye, S. Angew.
Chem., Int. Ed. 2001, 40, 2305−2308.
(19) Compounds 9a/b are prepared from serine ester HCl via Boc
protection followed by dehydration with MsCl/TEA. (a) Wang, H.;
Zhang, J.; Xian, M. J. Am. Chem. Soc. 2009, 131, 13238−13239.
(b) Ramesh, R.; De, K.; Chandrasekaran, S. Tetrahedron 2007, 63,
10534−10542.
(20) (a) 9a/b are highly prone to polymerization as neat oils even at
−20 °C. Improved stability of 9 was achieved by storing as a 0.9 M
DMF solution (∼4 vol DMF) with 0.1 wt % 4-methoxyphenol or 2,6-
D
Org. Lett. XXXX, XXX, XXX−XXX