Organic Letters
Letter
(6) For a review on Brook rearrangement, see: Brook, A. G. Acc.
Chem. Res. 1974, 7, 77. For the original paper, see: Brook, A. G. J. Am.
Chem. Soc. 1958, 80, 1886.
(7) For carboxylations of C(sp3)−Si bonds by a fluoride, see:
(a) Ohno, M.; Tanaka, H.; Komatsu, M.; Ohshiro, Y. Synlett 1991,
919. (b) Singh, R. P.; Shreeve, J. M. Chem. Commun. 2002, 38, 1818.
(c) Babadzhanova, L. A.; Kirij, N. V.; Yagupolskii, Y. L. J. Fluorine
Chem. 2004, 125, 1095. (d) Petko, K. I.; Kot, S. Y.; Yagupolskii, L. M.
J. Fluorine Chem. 2008, 129, 301.
For fluoride-mediated
carboxylations of C(sp2)−Si bonds, see: (e) Effenberger, F.;
Spiegler, W. Chem. Ber. 1985, 118, 3900. For fluoride-mediated
carboxylations of C(sp)−Si bonds, see: (f) Kobayashi, M.; Inamato,
K.; Tanaka, Y.; Kondo, Y. Org. Biomol. Chem. 2013, 11, 3773.
(8) For our recent achievements of carboxylations of benzylic and
allylic silanes by a fluoride, see: (a) Mita, T.; Michigami, K.; Sato, Y.
Org. Lett. 2012, 14, 3462. (b) Mita, T.; Chen, J.; Sugawara, M.; Sato, Y.
Org. Lett. 2012, 14, 6202.
(9) For KOt-Bu-mediated carboxylations of benzylic C(sp3)−B
bonds, see: Grigg, R. D.; Rigoli, J. W.; Hoveln, R. V.; Neale, S.;
Schomaker, J. M. Chem.Eur. J. 2012, 18, 9391.
(10) For alkylations with alkylbromides after fluoride-mediated 1,2-
Brook rearrangement, see: Brekan, J. A.; Chernyak, D.; White, K. L.;
Scheidt, K. A. Chem. Sci. 2012, 3, 1205.
(11) An, I.; Onyeozili, E. N.; Maleczka, R. E., Jr. Tetrahedron:
Asymmetry 2010, 21, 527.
(12) Mandelic acid (2a) could also be isolated as a phenethyl amine
salt form (88%) without using silica gel column chromatography. See
the Supporting Information for details. It can be transformed into
enantioenriched 2a by optical resolution. See: (a) Ingersoll, A. W.;
Babcock, S. H.; Burns, F. B. J. Am. Chem. Soc. 1933, 55, 411. For the
use of two structurally related resolving reagents for the optical
resolution of α-hydroxy acids (Dutch Resolution), see: (b) Vries, T.;
Wynberg, H.; Echten, E. V.; Koek, J.; Hoeve, W. T.; Kellogg, R. M.;
Broxterman, Q. B.; Minnaard, A.; Kaptein, B.; Sluis, S. V. D.; Hulshof,
L.; Kooistra, J. Angew. Chem., Int. Ed. 1998, 37, 2349. (c) Nieuwen-
huijzen, J. W.; Grimbergen, R. F. P.; Koopman, C.; Kellogg, R. M.;
Vries, T. R.; Pouwer, K.; Echten, E. V.; Kaptein, B.; Hulshof, L. A.;
Broxterman, Q. B. Angew. Chem., Int. Ed. 2002, 41, 4281.
(d) Dalmolen, J.; Tiemersma-Wegman, T. D.; Nieuwenhuijzen, J.
W.; Sluis, M. V. D.; Echten, E. V.; Vries, T. R.; Kaptein, B.;
Broxterman, Q. B.; Kellogg, R. M. Chem.Eur. J. 2005, 11, 5619.
(13) For a discussion of the solvent effect of carboxylation, see:
Kobayashi, K.; Kondo, Y. Org. Lett. 2009, 11, 2035.
(14) Optically active 1aa (92% ee) was subjected to the fluoride-
mediated carboxylation. As a result, 2a was obtained in racemic form,
suggesting that this Brook rearrangement−carboxylation reaction is
not stereospecific similar to the Scheidt’s case (ref 10). Optically active
1aa was prepared via enantioselective reduction of PhC(O)SiMe2Ph
using Noyori’s catalyst followed by the Me3Si-protection according to
the following literature. See: Huckins, J. R.; Rychnovsky, S. D. J. Org.
Chem. 2003, 68, 10135.
(15) LiSiMe2Ph can be easily generated from ClSiMe2Ph and Li
metal, and it smoothly reacts with many aldehydes to afford α-hydroxy
silanes. See: Barrett, A. G. M.; Hill, J. M. Tetrahedron Lett. 1991, 32,
3285.
(16) Moser, W. H. Tetrahedron 2001, 57, 2065.
(17) Partial silyl-deprotection of 7a occurred to produce
benzylalcohol because the PhMe2Si group seems to have lability
similar to that of the Me3Si group under basic conditions. For the use
of the Ph2MeSi group as a protecting group, see: Denmark, S. E.;
Hammer, R. P.; Weber, E. J.; Habermas, K. L. J. Org. Chem. 1987, 52,
165.
(18) The one-pot reaction of an α-alkyl aldehyde (3-phenyl
propionaldehyde) actually proceeded to afford 2m, albeit in low
yield (11% yield).
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dx.doi.org/10.1021/ol403099f | Org. Lett. XXXX, XXX, XXX−XXX