Highly concise and stereoselective total synthesis of (5R,7S)-kurzilactone

Article abstract of DOI:10.1002/hlca.201100466

A highly concise and stereoselective total synthesis of (5R,7S)-kurzilactone (1) was performed by a convergent approach by means of a Jacobsen's hydrolytic kinetic resolution, a Horner-Wadsworth-Emmons reaction for the construction of the α,β-unsaturated

Full text of DOI:10.1002/hlca.201100466

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Helvetica Chimica Acta – Vol. 95 (2012)
Highly Concise and Stereoselective Total Synthesis of (5R,7S)-Kurzilactone
by Debendra K. Mohapatra*, Pulluri Karthik, and Jhillu S. Yadav*
Natural Products Chemistry Division, CSIR-Indian Institute of Chemical Technology,
Hyderabad-500007, India (phone: þ 91-40-27193128; fax: þ 91-40-27160512;
e-mail: mohapatra@iict.res.in)
A highly concise and stereoselective total synthesis of (5R,7S)-kurzilactone (1) was performed by a
convergent approach by means of
a
Jacobsenꢀs hydrolytic kinetic resolution,
a
Hor-
nerꢀWadsworthꢀEmmons reaction for the construction of the a,b-unsaturated d-lactone ring system,
and a highly diastereoselective Mukaiyama aldol reaction for the introduction of the formal anti-1,3-diol
unit (Schemes 2 and 3).
Introduction. – Natural products possessing 6-substituted a,b-unsaturated-d-
lactone moieties have attracted the attention of synthetic organic chemists due to
their antitumor properties [1]. In addition, they inhibit HIV proteases [2], induce
apopotosis [3][4], and were shown to be antileukemic [5], along with having many
other relevant pharmacological properties [6]. (5R,7S)-Kurzilactone1) (1), an a,b-
unsaturated d-lactone, was isolated from the leaves of Cryptocarya kurzii, a plant that is
indigenous to Malaysia. Kurzilactone showed a marked cytotoxicity against the KB
human-carcinoma cell line (IC50 ¼ 1 mg/ml) [7]. Initially, the stereogenic centers
bearing the OH groups in the side chain and the O-atom of the d-lacton were assigned a
syn-relationship through NMR experiment but a corrected anti-relationship with
(5R,7S) configuration of the C(5) and C(7) stereogenic centers were later assigned on
the basis of a total synthesis [8]. The structural uniqueness of kurzilactone, coupled
with its interesting bioactivity and our interest to verify the selectivity of the
Mukaiyama aldol reaction in case of a d-lactone-substituted aldehyde instead of an
open-chain aldehyde as reported by our group, prompted us to revisit its total synthesis.
The retrosynthetic analysis of 1 is described in Scheme 1.
Results and Discussion. – Our initial approach to aldehyde 8 employed the oxirane
2 [9] (Scheme 2), prepared by Jacobsenꢀs hydrolytic kinetic resolution (HKR) [10] of
the racemate (Scheme 2) in the presence of [CoIII{(R,R)-ꢁsalenꢀ}(OAc)] catalyst
(ꢁsalenꢀ ¼ N,N’-bis[3,5-di(tert-butyl)salicylidene]cyclohexane-1,2-diaminato ¼ {{2,2’-
[(cyclohexane-1,2-diylbis(nitrilomethylidyne)]bis[4,6-di(tert-butyl)phenylato]}(2ꢀ)}.
The 4-methoxybenzyl(PMB)-protected (2R)-oxirane 2 was obtained as a single
enantionmer ([a]2D5 ¼ þ10.6 (c ¼ 1.2, CHCl3), ([11]: [a]D25 ¼ ꢀ13.1 (c ¼ 1.2, CHCl3)
for the (2S)-enantiomer)), which was easily separated from the more polar diol.
Oxirane 2 was treated with vinylmagnesium bromide in the presence of CuI to afford
1
)
Trivial atom numbering; for the systematic name, see Exper. Part.
ꢂ 2012 Verlag Helvetica Chimica Acta AG, Zꢃrich

Helvetica Chimica Acta – Vol. 95 (2012)
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Scheme 1. Retrosynthetic Analysis of (5R,7S)-Kurzilactone (1)
the homoallyl alcohol 3 in 85% yield. The spectral and analytical data of 3 (ee 94% by
HPLC)) were in good agreement with the literature values [12]. The C(3) stereogenic
center was further confirmed by a modified Mosherꢀs method [13]. (3S)-Alcohol 3 was
esterified with 2-(diethoxyphosphinyl)acetic acid 4 [14] in the presence of dicyclohex-
ylcarbodiimide (DCC) and a catalytic amount of N,N-dimethylpyridin-4-amine
(DMAP) to afford the (S)-ester 5 in 82% yield. Removal of the PMB group with
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (¼4,5-dichloro-3,6-dioxocyclohexa-1,4-di-
ene-1,2-dicarbonitrile; DDQ) [15] in CH2Cl2 yielded hydroxy derivative 6 in 90%
yield. Oxidation of 6 with 2-iodoxybenzoic acid (IBX) [16] followed by a Hor-
nerꢀWadsworthꢀEmmons reaction provided a,b-unsaturated d-lactone 7 in 68% yield
over two steps. The one-step conversion of the terminal olefin moiety of 7 to give
aldehyde 8 was achieved by a modified dihydroxylation followed by oxidative cleavage
of the diol in 91% yield [17].
Scheme 2. Synthesis of Aldehyde 8
a) Vinylmagnesium bromide, CuI THF, 08 to r.t., 2 h; 85%. b) (EtO)2P(O)CH2COOH (4), DCC,
DMAP, CH2Cl2, r.t., 12 h; 62%. c) DDQ, CH2Cl2, H2O, 08, 2 h; 90%. d) 1. IBX, DMSO, THF, 08 to r.t.,
6 h; 2. NaH, THF, 08, 2 h; 68% over two steps. e) OsO4, 2,6-lutidine (¼2,6-dimethylpyridine), NaIO4,
dioxane, H2O, r.t., 4 h; 91%.
Having aldehyde 8, the stage was set to carry out the crucial Mukaiyama aldol
reaction to verify the selectivity. The BF3 · Et2O-mediated Mukaiyama aldol reaction of
aldehyde 8 with trimethylsilyl enol ether 9 derived from (3E)-4-phenylbut-3-en-2-one

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Helvetica Chimica Acta – Vol. 95 (2012)
afforded the aldol adduct (5R,7S)-kurzilactone (1) as the only product in 95% yield
(Scheme 3). It is noteworthy to mention here that in case of the a,b-unsaturated-d-
lactone-substituted aldehyde 8, the cyclic transition state favored the attack from the
opposite face of the lactone center leading to exclusive (ꢁ 99%) formation of (5R,7S)-
kurzilactone (1). The spectral and analytical data of the synthetic (5R,7S)-kurzilactone
(1) were in good agreement with the reported value [8].
Scheme 3. Synthesis of (5R,7S)-Kurzilactone (1)
a) Et3N, CF 3SO3SiMe3, CH2Cl2, ꢀ 108, 30 min. b) 8, BF3 · Et2O, CH2Cl2, ꢀ 788, 2 h; 81% over two steps.
Conclusions. – We achieved the total synthesis of (5R,7S)-kurzilactone (1) in five
longest linear steps starting from a known oxirane by means of a Hornerꢀ
WadsworthꢀEmmons reaction for the construction of the a,b-unsaturated d-lactone
ring system and a highly diastereoselective Mukaiyama aldol reaction for the
introduction of the formal anti-1,3-diol unit. Following the same protocol, (5S,7R)-
kurzilactone (ent-1) could also be synthesized.
Experimental Part
General. Air- and/or moisture-sensitive reactions were carried out in anh. solvents under Ar in an
oven- or flame-dried glassware. All anh. solvents were distilled prior to use: THF, benzene, toluene and
Et2O from Na and benzophenone; CH2Cl2, quinoline, and Et3N from CaH2; MeOH from Mg cake.
Commercial reagents were used without purification. Column chromatography (CC): silica gel (SiO2,
60 – 120 mesh). Specific optical rotations: [a]D in 10ꢀ1 deg cm2 gꢀ1. IR Spectra: in CHCl3 or neat (as
mentioned); ˜n in cmꢀ1. 1H- and 13C-NMR Spectra: at 300 (1H) and 75 MHz (13C); in CDCl3; d in ppm rel.
to Me4Si as internal standard, J in Hz.
(3S)-1-[(4-Methoxyphenyl)methoxy]hex-5-en-3-ol (3). To a stirred soln. of 2 (5.0 g, 24.22 mmol)
and CuI (0.45 g, 2.40 mmol) in THF (30 ml) was added CH2¼CHMgBr (48 ml, 48.02 mmol) at ꢀ 108, and
stirred at ꢀ 108 for 1 h. After completion of the reaction (TLC monitoring), it was quenched with sat.
NH4Cl soln. (20 ml). The mixture was extracted with AcOEt (2 ꢂ 60 ml), the combined org. layer washed
with H2O (100 ml) and brine (100 ml), dried (Na2SO4), and concentrated, and the residue purified by CC
(SiO2): 3 (4.8 g, 85%). Light yellow liquid. Rf (AcOEt/hexane 3 :7) 0.4. [a]2D5 ¼ ꢀ6.2 (c ¼ 1.1, CHCl3)
([12]: [a]2D0 ¼ ꢀ5.8 (c ¼ 1.37, CHCl3)). IR (KBr): 2923, 2855, 2380, 1724, 1611, 1512, 1247, 1096, 1034, 822,
560. 1H-NMR: 7.25 (d, J ¼ 8.4, 2 H); 6.87 (d, J ¼ 8.4, 2 H); 5.80 – 5.72 (m, 1 H); 5.14 – 5.06 (m, 2 H); 4.45
(s, 2 H); 3.89 – 3.82 (m, 1 H); 3.80 (s, 3 H); 3.73 – 3.57 (m, 2 H); 2.27 – 2.20 (m, 2 H); 1.82 – 1.70 (m, 2 H);
13C-NMR: 159.1; 134.8; 129.9; 129.2; 117.4; 113.7; 72.8; 70.3; 68.5; 55.2; 41.8; 35.7. ESI-HR-MS: 259.1305
([M þ Na]þ, C14H20NaOþ3 ; calc. 259.1306).
(1S)-1-{2-[(4-Methoxyphenyl)methoxy]ethyl}but-3-en-1-yl 2-(Diethoxyphosphinyl)acetate (5). To a
stirred soln. of 2-(diethoxyphosphinyl)acetic acid (4; 4.5 g, 19.07 mmol) and DCC (7.9 g, 38.14 mmol) in
CH2Cl2 (50 ml), was added DMAP (1.1 g, 9.05 mmol) at r.t. The mixture was stirred for 15 min before a
soln. of 3 (7.4 g, 38 mmol) in CH2Cl2 (30 ml) was added at r.t. The mixture was stirred at r.t. for 12 h.
After completion of the reaction (TLC monitoring), the mixture was quenched with H2O (30 ml). The

Helvetica Chimica Acta – Vol. 95 (2012)
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aq. layer was extracted with CH2Cl2 (2 ꢂ 75 ml), the combined org. phase dried (Na2SO4), and
concentrated, and the residue purified by CC (SiO2): 5 (4.5 g, 62%). Colorless liquid. Rf (AcOEt/hexane
1:1) 0.3. [a]2D5 ¼ þ20.4 (c ¼ 1.5, CHCl3). IR (KBr): 3328, 2926, 2853, 1666, 1734, 1625, 1250, 1029, 966,
610. 1H-NMR: 7.24 (d, J ¼ 8.4, 2 H); 6.86 (d, J ¼ 8.4, 2 H); 5.73 – 5.69 (m, 1 H); 5.17 – 5.04 (m, 3 H); 4.39
(s, 2 H); 4.20 – 4.08 (m, 4 H); 3.82 – 3.76 (s, 3 H); 3.57 – 3.43 (m, 2 H); 2.92 (d, J ¼ 21.5, 2 H); 2.42 – 2.27
(m, 2 H); 1.91 – 1.80 (m, 2 H); 1.34 (dd, J ¼ 6.97, 0.37, 6 H). 13C-NMR: 164.4; 158.3; 132.4; 129.6; 128.5;
117.3; 112.9; 71.8; 71.4; 65.2; 61.7; 54.4; 37.8; 34.4; 33.2; 15.6. ESI-HR-MS: 437.1705 ([M þ Na]þ,
C20H32NaO7Pþ; calc. 437.1726).
(1S)-1-(2-Hydroxyethyl)but-3-en-1-yl 2-(Diethoxyphosphinyl)acetate (6). To a stirred soln. of 5
(4.5 g, 10.81 mmol) in CH2Cl2/H2O 9 :1 (50 ml) was added DDQ (2.9 g, 13.12 mmol) at 08, and the
mixture was stirred for 2 h. After completion (TLC monitoring), the reaction was quenched with sat. aq.
NaHCO3 soln. (25 ml). The mixture was filtered through Celite, the aq. layer extracted with CH2Cl2 (2 ꢂ
40 ml), the combined org. phase washed with H2O (50 ml) and brine (50 ml), dried (Na2SO4), and
concentrated, and the residue purified by CC (SiO2): 6 (2.87 g, 90%). Colorless liquid. Rf (AcOEt/hexane
4 :1) 0.2. [a]2D5 ¼ þ10.6 (c ¼ 1.7, CHCl3). IR (KBr): 2922, 2854, 2381, 1733, 1458, 1271, 1030, 970, 604, 494.
1H-NMR: 5.79 – 5.72 (m, 1 H); 5.16 – 5.04 (m, 3 H); 4.23 – 4.10 (m, 4 H); 3.72 – 3.57 (m, 2 H); 3.02 – 2.80
(m, 2 H); 2.44 – 2.32 (m, 2 H); 1.89 – 1.80 (m, 1 H); 1.75 – 1.66 (m, 1 H); 1.40 – 1.33 (m, 6 H). 13C-NMR:
165.9; 133.0; 118.0; 72.7; 63.0; 58.2; 38.7; 36.2; 33.5; 16.2. ESI-HR-MS: 295.1310 ([M þ H]þ, C12H24O6Pþ;
calc. 295.1305).
(6S)-5,6-Dihydro-6-(prop-2-en-1-yl)-2H-pyran-2-one (7). To a stirred soln. of iodoxybenzoic acid
(3.7 g, 13.22 mmol) in dry DMSO (10 ml), was added a soln. of 6 (2.6 g, 8.84 mmol) in anh. THF (35 ml)
at r.t. and stirred for 6 h. After completion of the reaction (TLC monitoring), the mixture was quenched
with H2O (20 ml) and filtered through Celite. The filtrate was extracted with AcOEt (3 ꢂ 50 ml). The
combined org. phase was washed with brine (75 ml), dried (Na2SO4), and concentrated, and the resulting
crude aldehyde (2.75 g) was used as such without further purification for the next step. To a suspension of
NaH (0.32 g, 13.62 mmol) in dry THF (60 ml), the crude aldehyde (2.75 g, 8.06 mmol) in THF (200 ml)
was added at 08, and the mixture was stirred for 2 h. After completion of the reaction (TLC monitoring),
it was quenched with H2O (30 ml). THF was removed, the aq. layer extracted with AcOEt (3 ꢂ 50 ml),
the combined org. phase dried (Na2SO4) and concentrated, and the residue purified by CC (SiO2): 7
(0.64 g, 68% over two steps). Colorless liquid. Rf (AcOEt/hexane 3 :7) 0.7. [a]2D5 ¼ þ84 (c ¼ 2.1, CHCl3).
1
IR (KBr): 2923, 2855, 1726, 1459, 1280, 1071, 526. H-NMR: 6.87 – 6.79 (m, 1 H); 6.00 (dt, J ¼ 9.8, 1.5,
1 H); 5.88 – 5.79 (m, 1 H); 5.20 – 5.11 (m, 2 H); 4.49 – 4.42 (m, 1 H); 2.62 – 2.40 (m, 2 H); 2.37 – 2.31 (m,
2 H). 13C-NMR: 164.2; 144.9; 132.2; 121.2; 118.8; 77.0; 39.0; 28.6. ESI-MS: 138 (Mþ).
(2R)-3,6-Dihydro-6-oxo-2H-pyran-2-acetaldehyde (8). To a stirred soln. of 7 (0.2 g, 1.42 mmol) in
dioxane/H2O 3 :1 (8 ml), 2,6-lutidine (0.31 g, 2.89 mmol), OsO4 (0.007 g, 0.028 mmol), and NaIO4
(1.23 g, 5.79 mmol) were added. The mixture was stirred at r.t. for 4 h (TLC monitoring). The mixture
was quenched with H2O (10 ml) and extracted with CH2Cl2 (3 ꢂ 30 ml). The combined org. phase was
washed with brine (50 ml), dried (Na2SO4), and concentrated, and the resulting crude 8 (208 mg, 91%)
was used as such without further purification in the next step.
{(1E)-3-[(Trimethylsilyl)oxy]buta-1,3-dien-1-yl}benzene (9). To a stirred soln. of (3E)-4-phenylbut-
3-en-2-one (0.5 g, 3.44 mmol) and Et3N (0.47 ml, 5.17 mmol) in freshly prepared anh. CH2Cl2 (10 ml) at
ꢀ 108 was added dropwise CF3SO3SiMe3 (0.8 ml, 4.10 mmol). The mixture was stirred at ꢀ 108 for
30 min and quenched with sat. aq. NaHCO3 soln. The aq. layer was extracted with CH2Cl2 (2 ꢂ 25 ml),
the combined org. phase dried (Na2SO4) and concentrated at r.t., and the resulting crude 9 (0.46 g) was
used as such for the next step without purification.
(6R)-5,6-Dihydro-6-[(2S,5E)-2-hydroxy-4-oxo-6-phenylhex-5-en-1-yl]-2H-pyran-2-one (1). Alde-
hyde 8 (0.208 g, 1.4 mmol) and silyl enol ether 9 (0.46 g, 2.12 mmol) were taken up in freshly prepared
anh. CH2Cl2 (20 ml), and the mixture was cooled to ꢀ 788. BF3 · Et2O (0.30 ml, 2.12 mmol) in freshly
prepared anh. CH2Cl2 (5 ml) was added slowly. The mixture was stirred at ꢀ 788 for additional 2 h and
quenched with sat. aq. NaHCO3 soln. (10 ml). The the aq. layer was extracted with CH2Cl2 (2 ꢂ 25 ml),
the combined org. phase washed with H2O (40 ml) and brine (40 ml), dried (Na2SO4), and concentrated,
and the residue purified by CC (SiO2): 1 (382 mg, 81% over two steps). White solid. Rf (AcOEt/hexane
1:3) 0.3. M.p. 73 – 748. [a]2D5 ¼ þ82.4 (c ¼ 1.0, CHCl3) ([8]: [a]D20 ¼ þ84 (c ¼ 0.231, CHCl3). IR (KBr):

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Helvetica Chimica Acta – Vol. 95 (2012)
3453, 3028, 2924, 2854, 1712, 1604, 1384, 1252, 1049, 781, 508. 1H-NMR: 7.58 (d, J ¼ 16.0, 1 H); 7.56 – 7.52
(m, 2 H); 7.43– 7.36 (m, 3 H); 6.94 – 6.91 (m, 1 H); 6.77 – 6.68 (d, J ¼ 16.0, 1 H); 6.02 (dd, J ¼ 9.8, 2.0,
1 H); 4.85 – 4.75 (m, 1 H); 4.54 – 4.46 (m, 1 H); 2.93 (dd, J ¼ 17.3, 3.0, 1 H); 2.81 (dd, J ¼ 17.3, 9.0, 1 H);
2.44 – 2.30 (m, 2 H); 1.93 – 1.78 (m, 2 H). 13C-NMR: 200.3; 164.2; 145.2; 143.8; 134.0; 130.8; 128.9; 128.4;
125.9; 121.3; 74.8; 63.9; 46.8; 41.6; 29.9. ESI-HR-MS: 309.1102 ([M þ Na]þ, C17H18NaO4þ ; calc.
309.1109).
REFERENCES
[1] H. M. R. Hoffmann, J. Rabe, Angew. Chem., Int. Ed. 1985, 24, 94.
[2] K. R. Romines, R. A. Chrusciel, Curr. Med. Chem. 1995, 2, 825; P. A. Aristoff, Drugs Future 1998, 23,
995; S. Hagen, J. V. N. V. Prasad, B. D. Tait, Adv. Med. Chem. 2000, 5, 159; S. E. Hagen, J. Domagala,
C. Gajda, M. Lovdahl, B. D. Tait, E. Wise, T. Holler, D. Hupe, C. Nouhan, A. Urumov, G. Zeikus, E.
Zeikus, E. A. Lunney, A. Pavlovsky, S. J. Gracheck, J. Saunders, S. VanderRoest, J. Brodfuehrer, J.
Med. Chem. 2001, 44, 2319; V. K. Agrawal, J. Singh, K. C. Mishra, P. V. Khadikar, Y. A. Jaliwala,
Arkivoc 2006, ii, 162.
[3] S. H. Inayat-Hussain, A. B. Osman, L. B. Din, N. Taniguchi, Toxicol. Lett. 2002, 131, 153; S. H.
Inayat-Hussain, B. O. Annuar, L. B. Din, A. M. Ali, D. Ross, Toxicol. In Vitro 2003, 17, 433; K. M.
Chan, N. F. Rajab, M. H. A. Ishak, A. M. Ali, K. Yusoff, L. B. Din, S. H. Inayat-Hussain, Chem.-Biol.
Interact. 2006, 159, 129.
[4] N. B. Blatt, G. D. Glick, Bioorg. Med. Chem. 2001, 9, 1371; Z. Huang, Chem. Biol. 2002, 9, 1059.
[5] H. Kikuchi, K. Sasaki, J. Sekiya, Y. Maeda, A. Amagai, Y. Kubohara, Y. Ohsima, Bioorg. Med.
Chem. 2004, 12, 3203.
[6] S. S. Stampwala, R. H. Bunge, T. R. Hurley, N. E. Willmer, A. J. Brankiewicz, C. E. Steinman, T. A.
Smitka, J. C. French, J. Antibiot. 1983, 36, 1601; H. Nagashima, K. Nakamura, T. Goto, Biochem.
Biophys. Res. Commun. 2001, 287, 829; G. E. Raoelison, C. Terreaux, E. F. Queiroz, F. Zsila, M.
Simonyi, S. Antus, A. Randriantsoa, K. Hostettmann, Helv. Chim. Acta 2001, 84, 3470; D. S. Lewy,
C.-M. Gauss, D. R. Soenen, D. L. Boger, Curr. Med. Chem. 2002, 9, 2005; A. K. Larsen, A. E.
Escargueil, A. Skladanowski, Pharmacol. Ther. 2003, 99, 167; A. Richetti, A. Cavallaro, T. Ainis, V.
Fimiani, Immunopharmacol. Immunotoxicol. 2003, 25, 441; F. Koizumi, H. Ishiguro, K. Ando, H.
Kondo, M. Yoshida, Y. Matsuda, S. Nakanishi, J. Antibiot. 2003, 56, 603.
´
[7] X. Fu, T. Sevenet, A. Hamid, A. Hadi, F. Remy, M. Paꢄs, Phytochemistry 1993, 33, 1272.
[8] B. Jiang, Z. Chen, Tetrahedron: Asymmetry 2001, 12, 2835.
[9] J. A. Marshall, G. Schaaf, A. Nolting, Org. Lett. 2005, 7, 5331.
[10] L. P. C. Nielsen, C. P. Stevenson, D. G. Blackmond, E. N. Jacobsen, J. Am. Chem. Soc. 2004, 126,
1360.
[11] M. J. Gaunt, A. S. Jessiman, P. Orsini, H. R. Tanner, D. F. Hook, S. V. Ley, Org. Lett. 2003, 5, 4819.
[12] D.-R. Li, D.-H. Zhang, C.-Y. Sun, J.-W. Zhang, L. Yang, J. Chen, B. Liu, C. Su, W.-S. Zhou, G.-Q. Lin,
Chem.ꢀEur. J. 2006, 12, 1185.
[13] I. Ohtani, J. Kusumi, Y. Kashman, H. Kakisawa, J. Am. Chem. Soc. 1991, 113, 4092; W. Y. Yoshido,
P. J. Bryan, B. J. Baker, J. B. McClintock, J. Org. Chem. 1995, 60, 780.
[14] A. Friese, K. Hell-Momeni, I. Zꢃndorf, T. Winckler, T. Dingermann, G. Danhardt, J. Med. Chem.
2002, 45, 1535; A. B. Smith, III, I. G. Safonov, R. M. Corbett, J. Am. Chem. Soc. 2002, 124, 11102;
K. C. Nicolaou, Y.-P. Sun, R. Guduru, B. Banerji, D. Y.-K. Chen, J. Am. Chem. Soc. 2008, 130, 3633;
K. Ando, K. Narumiya, H. Takada, T. Teruya, Org. Lett. 2010, 12, 1460.
[15] Y. Oikawa, T. Yushioka, O. Yonemitsu, Tetrahedron Lett. 1982, 23, 885.
[16] M. Frigeno, M. Santagostino, Tetrahedron Lett. 1994, 35, 8019.
[17] W. Yu, Y. Mei, Y. Kang, Z. Hua, Z. Jin, Org. Lett. 2004, 6, 3217.
Received November 23, 2011