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Diastereoselective Synthesis of γ-Butenolides Catalyzed by Potassium tert-ButoxideGuang-Fen Du a , Lin He a , Cheng-Zhi Gu a & Bin Dai aa Key Laboratory for Green Processing of Chemical Engineeringof Xinjiang Bingtuan and School of Chemistry and ChemicalEngineering, Shihezi University, Xin Jiang, P.R. ChinaAccepted author version posted online: 10 Oct 2011.Version ofrecord first published: 22 Dec 2011.

To cite this article: Guang-Fen Du , Lin He , Cheng-Zhi Gu & Bin Dai (2012): DiastereoselectiveSynthesis of γ-Butenolides Catalyzed by Potassium tert-Butoxide, Synthetic Communications: AnInternational Journal for Rapid Communication of Synthetic Organic Chemistry, 42:8, 1226-1233

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DIASTEREOSELECTIVE SYNTHESIS OFc-BUTENOLIDES CATALYZED BY POTASSIUMtert-BUTOXIDE

Guang-Fen Du, Lin He, Cheng-Zhi Gu, and Bin DaiKey Laboratory for Green Processing of Chemical Engineering of XinjiangBingtuan and School of Chemistry and Chemical Engineering, ShiheziUniversity, Xin Jiang, P.R. China

GRAPHICAL ABSTRACT

Abstract Potassium tert-butoxide (0.1mol%) catalyzed a vinylogous Mukaiyama aldol

reaction between aromatic and aliphatic aldehydes with 2-(trimethylsilyloxy)furan. The

corresponding c-butenolides were obtained in good yields with good diastereoselectivities.

Keywords Butenolides; 2-(trimethylsilyloxy)furan; vinylogous Mukaiyama aldol reaction

INTRODUCTION

The Mukaiyama aldol reaction[1] is a powerful method for a carbon–carbonbond-forming reaction in organic chemistry, which provides a reliable option forb-hydroxy carbonyl compounds via coupling of enolsilanes with aldehydes or ketones.Meanwhile, ifO-silylated dienolates react with carbonyl compounds at the c-position,a,b-unsaturated carbonyl compounds are obtained. This is the so-called vinylogousMukaiyama aldol (VMA) reaction, which has also been explored extensively.[2]

As important subunits in natural products[3] and valuable building blocks forthe synthesis of biologically active compounds,[4] c-substituted butenolides can beprepared through VMA reaction of 2-(trimethylsilyloxy)furan (TMSOF) and suitablecarbonyl compounds. To our knowledge, different Lewis acids such as aluminumalkoxide, bismuth triflate, iodine, SnCl4, ZnCl2, TiCl4, BF3 �OEt2, SiCl4, and silyltriflates[5] have been employed as effective catalysts for the synthesis of racemicc-substituted butenolides via VMA reaction.[6] However, in contrast to the study of

Received August 16, 2010.

Address correspondence to Lin He, School of Chemistry and Chemical Engineering, Shihezi

University, Xin Jiang 832000, P.R. China. E-mail: helin@shzu.edu.cn

Synthetic Communications1, 42: 1226–1233, 2012

Copyright # Taylor & Francis Group, LLC

ISSN: 0039-7911 print=1532-2432 online

DOI: 10.1080/00397911.2010.538888

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Lewis acid–catalyzed VMA reaction of TMSOF, the transformations promoted byLewis bases were far less examined.[7] Pioneering work done by Cahard et al.[8]

revealed that catalytic potassium tert-butoxide could promote the Mukaiyama aldolreaction of O-silylated acyclic dienolates with aldehydes efficiently. However, theycould not apply this catalytic system to the reaction of TMSOF. Herein, we reportthe preliminary results of potassium tert-butoxide–catalyzed VMA reaction ofTMSOF and aldehydes, giving c-substituted butenolides in good yields with gooddiastereoselectivities.

RESULTS AND DISCUSSION

Our initial reaction was conducted with TMSOF and p-chlorobenzaldehyde inthe presence of 1mol% of potassium tert-butoxide. Gratifyingly, this VMA reactionproceeded smoothly, providing the desired lactone in 94% yield with good diastereos-electivity (Table 1, entry 1). Stimulated by this result, different reaction conditionswere examined. Polar solvents such as tetrahydrofuran (THF), ether, and dioxanewere tested, and THF was found to be the most suitable to afford desired lactonein excellent yield and good diastereoselectivity (Table 1, entries 1–3). However,nonpolar reaction media such as toluene, benzene, and chlorobenzene gave the pro-duct in relatively poor yield but with good diastereoselectivity (Table 1, entries 4–6).tBuOH was also surveyed and similar results were obtained (Table 1, entry 7).Interestingly, temperatures lowered to 0 �C or even �20 �C resulted in no obvious

Table 1. tBuOK-catalyzed VMA reaction of TMSOF with p-chlorobenzaldehydea

Entry Solvent Yield (%)b anti=sync

1 THF 94 80:20

2 Ether 35 56:44

3 Dioxane 75 78:22

4 Toluene 30 70:30

5 Benzene 33 80:20

6 Chlorobenzene 32 80:20

7 tBuOH 42 79:21

8d THF 90 81:19

9e THF 91 80:20

10f THF 93 84:16

11g THF — —

aReaction conditions: 1a (1.2 equiv), 2a (1.0 equiv), tBuOK (1mol %).bYields after purification by column chromatography.csyn and anti ratio was determined by 1H NMR analysis of the crude products.dPerformed at 0 �C.ePerformed at �20 �C.f0.1mol % tBuOK was loaded.gNo tBuOK.

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improvements (Table 1, entries 8–9). To our delight, further decreasing the catalystloading to 0.1mol% maintained good yield and diastereoselectivity (Table 1, entry10). A control experiment showed no butenolide was obtained without catalysis oftBuOK (Table 1, entry 11).

Under optimized reaction conditions (THF, rt, 0.1mol% tBuOK), variousaldehydes were tested, and the results are summarized in Table 2. Both aromatic alde-hydes and cyclohexanecarboxaldehydes were suitable substrates for the couplingreaction. (Linear aliphatic aldehyde such as butyraldehyde was a unsuitable sub-strate; the isolated yield was less then 10%.) The VMA reaction of aromatic aldehydesbearing either electron-withdrawing or electron-donating groups proceeded smoothlyto provide the desired lactones in good yields and good diastereoselectivities (Table 2,entries 1–5). However, strong electron-withdrawing or donating electron-groupson the aromatic ring resulted in relatively lower yield but with no decrease of diaster-eoselectivities (Table 2, entries 2 and 4). Additionaly, different positions of thesubstituents on the aromatic ring resulted in no obvious impacts on the yield ordiastereoisomeric ratios (Table 2, entries 7–10). Interestingly, heteromatic aldehydealso proved suitable for the reaction (Table 2, entry 11). As expected, when cyclohex-anone was applied, the reaction proceeded sluggishly, presumablely because of its lowreactivity (Table 2, entry 13). It should be noted that most of the lactones were isolatedas a mixture of syn- and anti-isomers, with the anti-isomers as the major products.

In contrast to the pioneer work of Lewis base–catalyzed Mukaiyama aldolreaction,[8] we suggested that the Si-O bond of 2-(trimethylsilyloxy)furan was acti-vated by tBuOK and resulted in the formation of furan-based dienolate II, which

Table 2. tBuOK-catalyzed VMA reaction of TMSOF with aldehydesa

Entry R Time (h) Yield (%)b anti=sync

1 2a, 4-ClC6H4 12 93 84:16

2 2b, 4-NO2C6H4 12 67 75:25

3 2c, 4-FC6H4 12 79 87:13

4 2d, 4-MeOC6H4 24 68 81:19

5 2e, 4-MeC6H4 24 74 77:23

6 2f, C6H5 15 80 79:21

7 2g, 2-MeOC6H4 24 82 85:15

8 2h, 3-MeOC6H4 24 83 81:19

9 2i, 2-ClC6H4 15 80 83:17

10 2j, 2,4-Cl2C6H3 15 79 81:19

11 2k, 2-furyl 24 82 73:27

12 2l, cyclohexyl 12 57 81:19

13 2m, cyclohexanone 20 7 —

aReaction conditions: 1a (1.2 equiv), 2 (1.0 equiv), tBuOK (0.1mol %).bYields after purification by column chromatography.csyn and anti ratio was determined by 1H NMR analysis of the crude products.

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might trigger the addition of aldehydes and provide c-substituted butenolides(Scheme 1).

In summary, we have proved tBuOK to be an efficient catalyst for the VMAreaction of 2-(trimethylsilyloxy)furan with various aldehydes. The low catalyst load-ing and mild conditions provide novel access to c-substituted butenolides. Furtherstudies to examine the scope and generality of this methodology are under way inour laboratory.

EXPERIMENTAL

Unless otherwise indicated, all reactions were conducted under a nitrogenatmosphere in oven-dried glassware with a magnetic stirring bar. 1H NMR(400MHz) and 13C NMR (100MHz) spectra were recorded on a Varian Inova-400spectrometer in CDCl3, with tetramethylsilane (TMS) as an internal standard andare reported in parts per million (ppm, d). Infrared (IR) spectra were recorded on aNicolet FT=IR-360 spectrophotometer and reported as wave number (cm�1). Allstarting materials were obtained from commercial supplies and used as received.Solvents were purified by standard methods.

General Procedure for tBuOK-Catalyzed VMA Reaction ofTMSOF with Aldehydes

tBuOK (0.025M) in THF (20 mL, 0.1mmol%) was added to a solution ofaldehyde (0.25mmol) and TMSOF (0.3mmol) in 1.0mL tetrahydrofuran (THF)was added at 0 �C. The reaction mixture was stirred at rt until the starting aldehydewas consumed as indicated by thin-layer chromatography (TLC). The solution wasthen cooled to 0 �C and quenched with 10% aqueous HCl. The mixture was stirredfor 30min, neutralized by saturated aqueous NaHCO3, and then extrated with ethylacetate. The combined organic phase was dried over anhydrous Na2SO4, filtered,and concentrated. The ratio of anti=syn was determined by 1H NMR analysis of

Scheme 1. Proposed catalytic mechanism. (Figure is provided in color online.)

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the crude products, and the configurations were assigned by 1H NMR comparisonwith literature. The crude products were purified through silica-gel chromatography(ethyl acetate–petroleum ether) to afford pure anti-products or a mixture of anti=synisomers.

Representative Spectral Data

5-((4-Chlorophenyl)(hydroxyl)methyl)furan-2(5H)-one (3a).[6a] Compound3a was prepared according to the general procedure and purified by chromatographyon silica gel (PE–EtOAc, 4:1) to afford 3a as the pure anti-diastereoisomer, whitesolid (93%). 1H NMR (400MHz, CDCl3): d 7.42–7.28 (m, 5H), 6.11 (dd, J¼ 6.0,2.0Hz, 1H), 5.18–5.10 (m, 1H), 5.03 (t, J¼ 4.0Hz, 1H), 3.93 (d, J¼ 3.6Hz, 1H);13C NMR (100MHz, CDCl3): d 173.5, 153.1, 136.9, 134.1, 128.8, 127.6, 123.2,86.7, 72.2.

5-((4-Nitrophenyl)(hydroxyl)methyl)furan-2(5H)-one (3b).[6a] Compound3b was prepared according to the general procedure and purified by chromatographyon silica gel (PE–EtOAc, 3:1) to afford 3b as the pure anti-diastereoisomer, yellowsolid (67%). 1H NMR (400MHz, d6-DMSO): d 8.23 (d, J¼ 8.8Hz, 2H), 7.69(d, J¼ 8.8Hz, 2H), 7.65 (dd, J¼ 6.0, 1.6Hz, 1H), 6.28 (d, J¼ 5.2Hz, 1H), 6.24(dd, J¼ 5.6, 2.0Hz, 1H), 5.40–5.34 (m, 1H), 5.05 (t, J¼ 4.8Hz, 1H); 13C NMR(100MHz, CDCl3): d 172.7, 154.9, 147.0, 128.9, 123.1, 122.1, 85.8, 71.4.

5-((4-Fluorophenyl)(hydroxyl)methyl)furan-2(5H)-one (3c).[6a] Com-pound 3c was prepared according to the general procedure and purified by chroma-tography on silica gel (PE–EtOAc, 3:1) to afford 3c as the pure anti-diastereoisomer,white solid (79%). 1H NMR (400MHz, CDCl3): d 7.45–7.30 (m, 3H), 7.15–7.05 (m,2H), 6.16 (dd, J¼ 4.95, 2.0Hz, 1H), 5.18–5.12 (m, 1H), 5.06 (t, J¼ 4.4Hz, 1H), 3.27(d, J¼ 4.0Hz, 1H); 13C NMR (100MHz, CDCl3): d 173.1, 163.8, 161.4, 152.8, 134.1,134.0, 127.8, 127.7,123.2, 115.7, 115.5, 86.5, 72.4.

5-(Hydroxy)(4-methoxyphenyl)methyl)furan-2(5H)-one (3d).[5g,6a] Com-pound 3d was prepared according to the general procedure and purified by chroma-tography on silica gel (PE–EtOAc, 3:1) to afford 3d as a mixture of unseparablediastereoisomers, colorless oil (68%). 1H NMR (400MHz, CDCl3): d 7.38 [dd,J¼ 6.0, 1.6Hz, 1H (anti)], 7.33–7.23(m, 2H), 7.16 [dd, J¼ 5.6, 1.2Hz, 1H (syn)],6.95–6.85 (m, 2H), 6.14 [dd, J¼ 5.6, 1.6Hz, 1H (anti)], 6.08 [dd, J¼ 5.6, 2.0Hz,1H (syn)], 5.25–5.05 (m, 1H), 4.98 [d, J¼ 6.0Hz, 1H (anti)], 4.65 [d, J¼ 7.2Hz,1H (syn)], 3.81 (s, 3H); 13C NMR (100MHz, CDCl3): d 172.2, 158.6, 152.2, 129.4,126.3, 122.0, 113.0, 85.7, 71.8, 54.3.

5-(Hydroxy)(p-tolyl)methyl)furan-2(5H)-one (3e).[6a] Compound 3e wasprepared according to the general procedure and purified by chromatography on sil-ica gel (PE–EtOAc, 4:1) to afford 3e as a mixture of unseparable diastereoisomers,yellow solid (74%). 1H NMR (400MHz, CDCl3): d 7.35 (dd, J¼ 5.6, 1.6Hz, 1H),7.30–7.10 (m, 4H), 6.12 [dd, J¼ 5.6, 2.0Hz, 1H (anti)], 6.06 [dd, J¼ 6.0, 2.0Hz,1H (syn)], 5.20–5.10 (m, 1H), 5.01 [d, J¼ 4.4Hz, 1H (anti)], 4.66 [d, J¼ 7.2Hz,1H (syn)], 3.34 (br s, 1H), 2.35 (s, 3H); 13C NMR (100MHz, CDCl3): d 172.4,152.3, 137.1, 134.4, 128.3, 125.0, 121.9, 85.8, 71.8, 20.1.

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5-(Hydroxy)(phenyl)methyl)furan-2(5H)-one (3f).[5g,6a] Compound 3f wasprepared according to the general procedure and purified by chromatography on sil-ica gel (PE–EtOAc, 3:1) to afford 3f as a mixture of unseparable diastereoisomers,yellow oil (80%). 1H NMR (400MHz, CDCl3): d 7.41–7.30 (m, 6H), 6.12 [dd,J¼ 5.6, 2.0Hz, 1H (anti)], 6.06 [dd, J¼ 5.6, 2.0Hz, 1H (syn)], 5.20–5.10 (m, 1H),5.05 [d, J¼ 4.4Hz, 1H (anti)], 4.71 [d, J¼ 6.8Hz, 1H (syn)], 3.56 (br s, 1H); 13CNMR (100MHz, CDCl3): d 172.4, 152.2, 137.4, 127.7, 127.3, 125.1, 122.0, 85.8, 71.8.

5-(Hydroxy)(2-methoxyphenyl)methyl)furan-2(5H)-one (3g).[5a] Com-pound 3g was prepared according to the general procedure and purified by chroma-tography on silica gel (PE–EtOAc, 4:1) to afford 3g as the pure anti-diastereoisomer,yellow oil (82%). 1H NMR (400MHz, CDCl3): d¼ 7.42 (dd, J¼ 7.6, 1.6Hz, 1H),7.36–7.24 (m, 2H), 7.00 (dt, J¼ 7.2, 0.8Hz, 1H), 6.90 (dd, J¼ 8.4, 0.8Hz, 1H),6.11 (dd, J¼ 5.6, 1.2Hz, 1H), 5.50–5.20 (m, 2H), 3.86 (s, 3H), 3.62 (d, J¼ 3.6Hz,1H); 13C NMR (100MHz, CDCl3) d¼ 172.6, 154.9, 152.6, 128.3, 126.3, 125.2,121.7, 119.9, 109.3, 84.3, 67.7, 54.3.

5-(Hydroxy)(3-methoxyphenyl)methyl)furan-2(5H)-one (3h).[5a] Com-pound 3h was prepared according to the general procedure and purified by chroma-tography on silica gel (PE–EtOAc, 4:1) to afford 3h as a mixture of unseparablediastereoisomers, yellow oil (83%). 1H NMR (400MHz, CDCl3): d¼ 7.34 [dd,J¼ 6.0, 1.6Hz, 1H (anti)], 7.32–7.22 (m, 1H), 7.18 [dd, J¼ 6.0, 2.0Hz, 1H (syn)],7.0–6.8 (m, 3H), 6.11 [dd, J¼ 5.6, 2.0Hz, 1H (anti)], 6.06 [dd, J¼ 5.6, 2.0Hz, 1H(syn)], 5.20–5.10 (m, 1H), 5.03 [d, J¼ 5.0Hz, 1H (anti)], 4.67 [d, J¼ 6.8Hz, 1H(syn)], 3.79 (s, 3H), 3.70 (br s, 1H); 13C NMR (100MHz, CDCl3) d¼ 172.4, 158.7,152.2, 139.1, 128.7, 121.9, 117.3, 112.7, 110.6, 85.8, 71.6, 54.2.

5-((2-Chlorophenyl)(hydroxyl)methyl)furan-2(5H)-one (3i). Compound 3i

was prepared according to the general procedure and purified by chromatography onsilica gel (PE–EtOAc, 3:1) to afford 3i as the pure anti-diastereoisomer, white solid(80%); Rf¼ 0.14 (PE–EtOAc, 4:1); mp. 134.5–135.5 �C; 1H NMR (400MHz, CDCl3)d¼ 7.61 (dd, J¼ 7.6, 1.2Hz, 1H), 7.20–7.45 (m, 4H), 6.20 (dd, J¼ 5.6, 2.0Hz, 1H),5.62 (t, J¼ 4.0Hz, 1H), 5.36–5.44 (m, 1H), 3.36 (d, J¼ 4.4Hz, 1H); 13C NMR(100MHz, CDCl3) d¼ 172.3, 151.2, 134.5, 130.8, 128.6, 126.9, 126.4, 122.5, 83.6,68.4; IR (KBr) n 3390, 1726, 1465, 1437, 1342, 1188, 1108, 1025, 918, 819, 744,609 cm�1; HRMS (ESI) calcd. for C11H9ClO3Na: 247.0132; found: 247.0156.

5-((2,4-Dichlorophenyl)(hydroxyl)methyl)furan-2(5H)-one (3j).[6a] Com-pound 3j was prepared according to the general procedure and purified by chroma-tography on silica gel (PE–EtOAc, 4:1) to afford 3j as the pure anti-diastereoisomer,white solid (79%). 1H NMR (400MHz, CDCl3): d¼ 7.56 (d, J¼ 8.4Hz, 1H), 7.42(d, J¼ 2.0Hz, 1H), 7.35 (dd, J¼ 8.4, 2.0Hz, 1H), 7.24 (dd, J¼ 6.0, 1.6Hz, 1H),6.21 (dd, J¼ 5.6, 2.0Hz, 1H), 5.56 (t, J¼ 4.0Hz, 1H), 5.44–5.34 (m, 1H), 3.65(d, J¼ 4.4Hz, 1H); 13C NMR (100MHz, CDCl3) d¼ 172.3, 151.0, 133.8, 133.1,131.4, 128.3, 127.9, 126.7, 122.6, 83.4, 68.0.

5-(Furan-2-yl(hydroxyl)methyl)furan-2(5H)-one (3k).[5g] Compound 3k wasprepared according to the general procedure and purified by chromatography onsilica gel (PE–EtOAc, 4:1) to afford 3k as a mixture of unseparable diastereoisomers,

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brown oil (82%). 1H NMR (400MHz, CDCl3): d¼ 7.58 [dd, J¼ 6.0, 1.6Hz, 1H(anti)], 7.44–7.39 (m, 1H), 7.37 [dd, J¼ 6.0, 1.6Hz, 1H (syn)], 6.44–6.34 (m, 2H),6.17 [dd, J¼ 6.0, 2.0Hz, 1H (anti)], 6.14 [dd, J¼ 6.0, 2.0Hz, 1H (syn)], 5.34–5.28(m, 1H), 5.02 [d, J¼ 4.8Hz, 1H (anti)], 4.81 [d, J¼ 6.0Hz, 1H (syn)], 3.75 (br s,1H); 13C NMR (100MHz, CDCl3) d¼ 172.3, 152.6, 150.5, 141.7, 122.0, 109.6,107.4, 83.6, 66.4.

5-(Cyclohexxyl(hydroxyl)methyl)furan-2(5H)-one (3l).[5b,5c] Compound3l was prepared according to the general procedure and purified by chromatographyon silica gel (PE–EtOAc, 3:1) to afford 3l as the pure anti-diastereoisomer, colorlessoil (57%). 1H NMR (400MHz, CDCl3): d¼ 7.61 (dd, J¼ 5.6, 1.2Hz, 1H), 6.17 (dd,J¼ 5.6, 2.0Hz, 1H), 5.13–5.09 (dt, J¼ 5.6, 2.0Hz, 1H), 3.60 (q, J¼ 4.2Hz, 1H), 2.66(br s, 1H), 2.10–1.90 (m, 1H), 1.86–1.74 (m, 2H), 1.74–1.65 (m, 2H), 1.63–1.54 (m,1H), 1.40–1.00 (m, 5H); 13C NMR (100MHz, CDCl3) d¼ 173.3, 154.5, 122.5,83.9, 75.4, 40.6, 29.2, 27.8, 26.1, 25.9, 25.6.

ACKNOWLEDGMENT

This work was supported by the Start-Up Foundation for Young Scientists ofShihezi University (RCZX200806).

REFERENCES

1. For reviews, see (a) Shiina, I. In Modern Aldol Reactions; R. Mahrwald (Ed.); Wiley-VCH:Weinheim, 2004; vol. 2, pp. 105–166; (b) Mukaiyama, T.; Matsuo, J.-I. In Modern AldolReactions; R. Mahrwald (Ed.); Wiley-VCH: Weinheim, 2004; vol. 1, pp. 127–160; (c)Carreira, E. M. In Comprehensive Asymmetric Catalysis I–III; E. N. Jacobsen, A. Pfaltz,and H. Yamamoto (Eds.); Springer-Verlag: Berlin, Germany, 1999; vol. 3, pp. 997–1065.For a recent study of Mukaiyama aldol reaction, see (d) Curti, C.; Ranieri, B.; Battistini,L.; Rassu, G.; Zambrano, V.; Pelosi, G.; Casiraghi, G.; Zanardi, F. Catalytic, asymmetricvinylogous Mukaiyama aldol reactions of pyrrole- and furan-based dienoxy silanes: Howthe diene heteroatom impacts stereocontrol. Adv. Synth. Catal. 2010, 352, 2011; (e) Frings,M.; Goedert, D.; Bolm, C. Enantioselective synthesis of highly functionalised amides bycopper-catalysed vinylogous Mukaiyama aldol reaction. Chem. Commun. 2010, 46, 5497;(f) Yamaoka, M.; Nakazaki, A.; Kobayashi, S. Rate enhancement by water in a TiCl4-mediated stereoselective vinylogous Mukaiyama aldol reaction. Tetrahedron Lett. 2010,51, 287; (g) Curti, C.; Sartori, A.; Battistini, L.; Rassu, G.; Burreddu, P.; Zanardi, F.;Casiraghi, G. Vicarious silylative Mukaiyama aldol reaction: A vinylogous extension. J.Org. Chem. 2008, 73(14), 5446; (h) Shinoyama, M.; Shirokawa, S.; Nakazaki, A.;Kobayashi, S. A switch of facial selectivities using a-heteroatom-substituted aldehydes inthe vinylogous Mukaiyama aldol reaction. Org. Lett. 2009, 11(6), 1277; (i) Simsek, S.;Kalesse, M. Enantioselective synthesis of polyketide segments through vinylogousMukaiyama aldol reactions. Tetrahedron Lett. 2009, 50(26), 3485.

2. For reviews of vinylogous aldol reactions, see (a) Rassu, G.; Zanardi, F.; Battistini, L.;Casiraghi, G. The vinylogous aldol addition of heterocyclic silyloxy dienes: Applicationin synthesis. Synlett. 1999, 1333; (b) Casiraghi, G.; Zanardi, F.; Appendino, G.; Rassu,G. The vinylogous aldol reaction: A valuable, yet understated carbon–carbon bond-form-ing maneuver. Chem. Rev. 2000, 100, 1929; (c) Denmark, S. E.; Heemstra Jr., J. R.;

Beutner, G. L. Catalytic, enantioselective, vinylogous aldol reactions. Angew. Chem. Int.

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Ed. 2005, 44, 4682; (d) Kalesse, M. Recent advances in vinylogous aldol reactions and theirapplications in the syntheses of natural products. Top. Curr. Chem. 2005, 244, 43.

3. For reviews on butenolide-containing natural products, see (a) Rodriguez, A. D. The natu-ral products chemistry of West Indian gorgonian octocorals. Tetrahedron 1995, 51, 4571;(b) Alali, F. W.; Liu, X. X.; McLaughlin, J. L. Annonaceae acetogenin: Recent progress.

J. Nat. Prod. 1999, 62, 504; (c) Hanson, J. R. Steroids: Reactions and partial synthesis.Nat. Prod. Rep. 2002, 19, 381.

4. (a) Ferrie, S.; Reymond, S.; Capdevielle, P.; Cossy, J. Concise total synthesis of (�)-Muricatacin and (�)-iso-Cladospolide B using chemoselective cross-metathesis. Synlett2007, 18, 2891; (b) Sarma, K. D.; Zhang, J.; Curran, T. T. Novel synthons from mucochlo-ric acid: The first use of a,b-dichloro-c-butenolides and c-butyrolactams for direct

vinylogous aldol addition. J. Org. Chem. 2007, 72, 3311, and references therein.5. (a) Raders, S. M.; Verkade, J. G. Catalysis of Mukaiyama aldol reactions by a tricyclic

aluminum alkoxide Lewis acid. J. Org. Chem. 2009, 74, 5417; (b) Ollevier, T.; Bouchard,J. E.; Desyroy, V. Diastereoselective Mukaiyama aldol reaction of 2-(trimethylsilyloxy)-

furan catalyzed by bismuth briflate. J. Org. Chem. 2008, 73, 331; (c) Yadav, J. S.; SubbaReddy, B. V.; Narasimhulu, G.; Satheesh, G. Iodine as a mild and efficient catalyst forthe diastereoselective synthesis of d-silyloxy-c-lactones. Tetrahedron Lett. 2008, 49, 5683;(d) Acocella, M. R.; De Rosa, M.; Massa, A.; Palombi, L.; Villano, R.; Scettri, A. Silicontetrachloride in organic synthesis: New applications for the vinylogous aldol reaction. Tetra-hedron 2005, 61, 4091; (e) Kong, K.; Romo, D. Diastereoselective, vinylogous Mukaiyama

aldol additions of silyloxy furans to cyclic ketones: Annulation of butenolides andc-lactones. Org. Lett. 2006, 8, 2909; (f) Lopez, C. S.; Alvarez, R.; Vaz, B.; Faza, O. N.;de Lera, A. R. Simple diastereoselectivity of the BF3 �OEt2-catalyzed vinylogousMukaiyama aldol reaction of 2-(trimethylsiloxy)furans with aldehydes. J. Org. Chem.2005, 70, 3654; (g) Palombi, L.; Acocella, M. R.; Celenta, N.; Massa, A.; Villano, R.; Scettri,A. Highly enantioselective vinylogous addition of 2-trimethylsilyloxyfuran to aldehydespromoted by the SiCl4=chiral Lewis base system. Tetrahedron: Asymmetry 2006, 17, 3300.

6. For recent asymmetric vinylogous Mukaiyama aldol reaction of 2-(trimethylsilyloxy) furan,see (a) Zhu, N.; Ma, B. C.; Zhang, Y.; Wang, W. Organocatalyzed highly enantioselectiveand anti-selective construction of c-butenolides through vinylogous Mukaiyama aldol reac-tion. Adv. Synth. Catal. 2010, 352, 1291; (b) Szlosek, M.; Figadere, B. Highly enatioselectivealdol reaction with 2-(trimethylsilyloxy) furan: The first catalytic asymmetric autoinductivealdol reaction. Angew. Chem. Int. Ed. 2009, 48, 1799; (c) Frings, M.; Atodiresei, I.; Runsink,

J.; Raabe, G.; Bolm, C. Catalyzed vinylogous Mukaiyama aldol reactions with controlledenantio- and diastereoselectivities. Chem. Eur. J. 2009, 15, 1566; (d) Fabra, M. J.; Fraile,J. M.; Herrerıas, C. I.; Lahoz, F. J.; Mayoral, J. A.; Perez, I. Surface-enhanced stereoselec-tivity in Mukaiyama aldol reactions catalyzed by clay-supported bis(oxazoline)–copper

complexes.Chem. Commun. 2008, 5402; (e) Rosa,M. D.; Citro, L.; Soriente, A. The first orga-nocatalytic addition of 2-trimethylsilyloxyfuran to carbonyl compounds: Hydrogen-bondcatalysis in c-butenolides synthesis. Tetrahedron Lett. 2006, 47, 8507; (f) Nagao, H.; Yamane,

Y.; Mukaiyama, T. Effective synthesis of 5-substituted butenolide derivatives by usingcinchonidine-derived quaternary ammonium phenoxide catalyst. Chem. Lett. 2007, 36, 8.

7. (a) Chintareddy, V. R.; Wadhwa, K.; Verkade, J. G. P(PhCH2NCH2CH2)3N catalysis ofMukaiyama aldol reactions of aliphatic, aromatic, and heterocyclic aldehydes and trifluor-omethyl phenyl ketone. J. Org. Chem. 2009, 74, 8118, and references therein; (b) Hatano,M.; Suzuki, S.; Takagi, E.; Ishihara, K. Highly efficient synthesis of functionalized tertiaryalcohols catalyzed by potassium alkoxide–crown ether complexes. Tetrahedron Lett. 2009,50, 3171.

8. Cahard, D.; Duhamel, L.; Lecomte, S.; Poirier, J.-M. Prenylation reaction performed withcatalytically generated potassium prenal dienolate. Synlett 1998, 1399.

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