ChemComm
Communication
(c) M. Suginome and Y. Ito, Chem. Rev., 2000, 100, 3221;
(d) E. Hartmann and M. Oestreich, Chim. Oggi, 2011, 29, 34.
2 (a) I. Fleming, R. Henning and H. Plaut, J. Chem. Soc., Chem.
Commun., 1984, 29; (b) I. Fleming and P. E. J. Sanderson, Tetra-
hedron Lett., 1987, 28, 4229; (c) K. Tamao, N. Ishida, T. Tanaka and
M. Kumada, Organometallics, 1983, 2, 1694; (d) K. Tamao, T. Tanaka,
T. Nakajima, R. Sumiya, H. Arai and Y. Ito, Tetrahedron Lett., 1986,
27, 3377; (e) I. Fleming, A. Barbero and D. Walter, Chem. Rev., 1997,
97, 2063; ( f ) I. Fleming, in Science of Synthesis, ed. I. Fleming,
Thieme, Stuttgart, 2002, vol. 4, pp. 927–946.
3 For other approaches to racemic b-silyl carbonyls see:
(a) L. Iannazzo and G. A. Molander, Eur. J. Org. Chem., 2012, 4923;
(b) B. H. Lipshutz, J. A. Sclafani and T. Takanami, J. Am. Chem. Soc.,
1998, 120, 4021; (c) G. Auer, B. Weiner and M. Oestreich, Synthesis,
2006, 2113; (d) H. Ito, T. Ishizuka, J.-i. Tateiwa, M. Sonoda and
A. Hosomi, J. Am. Chem. Soc., 1998, 120, 11196; (e) C. T. Clark,
J. F. Lake and K. A. Scheidt, J. Am. Chem. Soc., 2004, 126, 84;
( f ) M. Oestreich and B. Weiner, Synlett, 2004, 2139.
4 (a) T. Hayashi, Y. Matsumoto and Y. Ito, J. Am. Chem. Soc., 1988,
110, 5579; (b) Y. Matsumoto, T. Hayashi and Y. Ito, Tetrahedron,
1994, 50, 335.
5 For a review of Si–B chemistry, see: T. Ohmura and M. Suginome,
Bull. Chem. Soc. Jpn., 2009, 82, 29.
Scheme 1 Catalytic asymmetric approach to (+)-blastmycinone.
To further explore the scope of the protocol, the kinetic
resolution of a series of 5-substituted butenolides was carried
out using Cu(I)–NHC catalysed asymmetric silyl transfer.14 Pleas-
ingly, treatment of 5-substituted butenolides with 60–70 mol% of
PhMe2SiBpin and the C2-symmetric catalyst derived from L8 and
CuI afforded silylated products after kinetic resolution in good
yields (up to a maximum of 50%), good enantiomeric ratios and
as single anti-diastereoisomers (Table 4).15
The rate of addition to 5-substituted butenolides was slower
than silyl transfer to unsubstituted lactones, presumably due to
increased steric hindrance, therefore higher catalyst and silyl-
borane loading was required.17 Primary alkyl, allyl, benzyl and
phenyl substituents at the 5-position of butenolides were found
to be compatible with the process. To our knowledge, these
examples represent the first kinetic resolutions achieved by
Cu-catalysed silyl transfer from a Si–B reagent.
6 (a) C. Walter, G. Auer and M. Oestreich, Angew. Chem., Int. Ed., 2006,
45, 5675; (b) C. Walter and M. Oestreich, Angew. Chem., Int. Ed.,
¨
2008, 47, 3818; (c) C. Walter, R. Frohlich and M. Oestreich, Tetra-
hedron, 2009, 65, 5513.
7 For NHCs in metal catalysis, see: (a) S. Dıez-Gonzalez, N. Marion
´
´
´
´
and S. P. Nolan, Chem. Rev., 2009, 109, 3612; (b) S. Dıez-Gonzalez
and S. P. Nolan, Aldrichimica Acta, 2008, 41, 43; (c) F. Glorius, Topics
in Organometallic Chemistry, N-Heterocyclic Carbenes in Transition
Metal Catalysis, Springer-Verlag, Berlin, Heidelberg, 2006, vol. 21,
pp. 1–218.
8 (a) K.-S. Lee and A. H. Hoveyda, J. Am. Chem. Soc., 2010, 132, 2898;
(b) K.-S. Lee, H. Wu, F. Haeffner and A. H. Hoveyda, Organometallics,
2012, 31, 7823; For a metal-free catalytic C–Si bond formation, see:
J. M. O’Brien and A. H. Hoveyda, J. Am. Chem. Soc., 2011, 133, 7712.
9 For alternative asymmetric approaches to b-silyl carbonyl
compounds, see: (a) I. Ibrahem, S. Santoro, F. Himo and
´
A. Cordova, Adv. Synth. Catal., 2011, 353, 245; (b) A. Welle,
To demonstrate the value of Cu(I)–NHC catalysed asym-
metric silyl transfer to unsaturated lactones, we report a concise
approach to (+)-blastmycinone, a natural product arising from
the hydrolysis of the antibiotic (+)-antimycin A3 (Scheme 1).18
Alkylation of silylated lactone 3 (see entry 1, Table 4) provided 4
with three contiguous stereocenters as a single diastereoisomer.
Fleming–Tamao oxidation2 then gave lactone 5, which after
esterification afforded (+)-blastmycinone.19
J. Petrignet, B. Tinanat, J. Wouters and O. Riant, Chem.–Eur. J.,
2010, 16, 10980; (c) B. H. Lipshutz, N. Tanaka, B. R. Taft and
C.-T. Lee, Org. Lett., 2006, 8, 1963; (d) R. Shintani, K. Okamoto
and T. Hayashi, Org. Lett., 2005, 7, 4757; (e) M. A. Kacprzynski,
S. A. Kazane, T. L. May and A. H. Hoveyda, Org. Lett., 2007, 9, 3187.
10 (a) S. Kehrli, D. Martin, D. Rix, M. Mauduit and A. Alexakis,
Chem.–Eur. J., 2010, 16, 9890; (b) D. Martin, S. Kehrli,
M. d’Augustin, H. Clavier, M. Mauduit and A. Alexakis, J. Am. Chem.
Soc., 2006, 128, 8416; (c) L. Liang, T. T.-L. Au-Yeung and A. S. C.
Chan, Org. Lett., 2002, 4, 3799.
In summary, we have explored the scope of a convenient
procedure for asymmetric silyl transfer to unsaturated lactones.
The Cu(I)–NHC catalysed process delivers b-silylated lactones in
good yields and enantioselectivities. In contrast to observations with
other substrate classes, the use of C2-symmetric imidazolinium salts
as NHC precursors was crucial for efficient asymmetric silyl transfer
to unsaturated 5-membered lactones. Kinetic resolution using
Cu-catalysed silyl transfer from a Si–B reagent has been applied to
racemic 5-butenolides and affords products with good enantio-
control and excellent diastereocontrol. The method has been used
in an expedient asymmetric synthesis of (+)-blastmycinone.
We thank The Leverhulme Trust (V.P.) and the EPSRC (J.P.R.)
for funding and Robyn Bullough for assistance optimising the
conversion of 3–5.
11 (a) For a reductive dynamic kinetic resolution of similar substrates,
see: M. P. Rainka, J. E. Milne and S. L. Buchwald, Angew. Chem., Int.
Ed., 2005, 44, 6177; (b) For kinetic resolutions of similar substrates
using organolithiums, see: S. H. Lim and P. Beak, Org. Lett., 2002,
4, 2657.
12 For a preliminary result, see: H. Y. Harb, K. D. Collins, J. V. G. Altur,
S. Bowker, L. Campbell and D. J. Procter, Org. Lett., 2010, 12, 5446.
13 The use of CuCN was ineffective.
14 (a) For the kinetic resolution of racemic 1-alkyl-2-methylenecyclo-
propanes using PhMe2SiBpin and Pd-catalysis, see: T. Ohmura,
H. Taniguchi and M. Suginome, Org. Lett., 2009, 11, 2880; (b) For
the two-directional desymmetrization of a,b-unsaturated esters
using PhMe2SiBpin and Rh-catalysis, see: E. Hartmann and
M. Oestreich, Org. Lett., 2012, 14, 2406.
15 I. Fleming, N. L. Reddy, K. Takaki and A. C. Ware, J. Chem. Soc.,
Chem. Commun., 1987, 1472.
16 (a) E. Vedejs and M. Jure, Angew. Chem., Int. Ed., 2005, 44, 3974;
(b) H. B. Kagan and J. C. Fiaud, Top. Stereochem., 1988, 18, 249.
17 Iso-propyl 5-substituted butenolide resulted in low conversion
(ca. 10%) but good enantiocontrol (er 87 : 13). Attempted addition to
the analogous tert-butyl substituted lactone resulted in no conversion.
18 M.-J. Chen, C.-Y. Lo, C.-C. Chin and R.-S. Liu, J. Org. Chem., 2000,
65, 6362.
Notes and references
1 For selected reviews, see: (a) M. Oestreich, E. Hartmann and
M. Mewald, Chem. Rev., 2013, 113, 402; (b) E. Hartmann, 19 R. S. Ferrarini, A. A. Dos Santos and J. V. Comasseto, Tetrahedron,
D. J. Vyas and M. Oestreich, Chem. Commun., 2011, 47, 7917;
2012, 68, 10601 and references cited therein.
c
5152 Chem. Commun., 2013, 49, 5150--5152
This journal is The Royal Society of Chemistry 2013