Topics in Catalysis Vol. 19, No. 1, March 2002 43

Catalytic Friedel–Crafts acylation of heteroaromatics

Ichiro Komoto, Jun-ichi Matsuo and Shu Kobayashi∗

Graduate School of Pharmaceutical Sciences, The University of Tokyo, CREST, Japan Science and Technology Corporation (JST), Hongo,Bunkyo-ku, Tokyo 113-0033, Japan

Catalytic Friedel–Crafts acylation of heteroaromatics has been achieved using metal triflates as catalysts. While conventional Friedel–Crafts acylation often requires the use of more than stoichiometric amounts of aluminum chloride, metal triflates such as tin(II) triflate,scandium triflate, and gallium triflate,etc. have enabled efficient acylation reactions by catalytic use.

KEY WORDS: Friedel–Crafts; acylation; heteroaromatics

1. Introduction

Friedel–Crafts acylation provides a fundamental methodfor the preparation of aromatic ketones, which are usefulintermediates for the synthesis of pharmaceuticals, agri-cultural chemicals,etc. While more than stoichiometricamounts of aluminum chloride (AlCl3) are needed in con-ventional Friedel–Crafts acylation [1], treatment of alu-minum residues after reactions sometimes induce environ-mental pollution problems in industrial scale synthesis. Toaddress this issue, we and others have investigated catalyticFriedel–Crafts acylation, and several excellent catalysts havebeen developed. [2] Among these catalysts, metal perfluo-roalkanesulfonates were found to be excellent [3], and cat-alytic Friedel–Crafts acylation of even deactivated benzenessuch as chlorobenzene and dichlobenzene as well as anilinederivatives has been successfully performed using hafniumand gallium perfluoroalkanesulfonates [4].

On the other hand, acylation of heteroaromatics such asfuran, thiophene, pyrrole, and indole derivatives has notbeen well studied [5] in comparison with that of benzenederivatives. Since the products, heteroaromatic ketones, arepotentially useful intermediates for the synthesis of pharma-ceuticals [6], we decided to investigate the use of metal per-fluoroalkanesulfonates as catalysts in the acylation of het-eroaromatics.

2. Results and discussion

First, we tested the reaction of furan with acetic anhy-dride using several Lewis acids, and the results are summa-rized in table 1. While AlCl3 gave the desired ketone in4% yield, metal triflates gave much better yields. Amongmetal triflates tested, it is noted that tin(II) triflate (Sn(OTf)2)gave the best result, and that the desired acetylated furanwas obtained in 86% yield when the reaction was carriedout in nitromethane. Other acylating agents were used un-der the optimized conditions, and in all cases the desired

∗ To whom correspondence should be addressed.

adducts were obtained in excellent yields (table 2). In ad-dition, acetylation of thiophene also proceeded smoothly inthe presence of 5 mol% of Sn(OTf)2. In this case, scandiumtriflate, a water-compatible Lewis acid that can be recover-able and reusable [7], was also effective to afford the desiredketone in 87% yield (table 3).

We next examined the acetylation of 2,3-benzofuran withacetic anhydride. 2,3-benzofuran was less reactive thanfuran, and only 30% yield of the desired ketone was ob-tained using Sn(OTf)2 as a catalyst. In addition, the productwas a mixture of 2-acylated (1) and 3-acylated (2) adducts

Table 1Effect of Lewis acids and solvents

Entry Lewis acid Solvent Yield (%)

1 AlCl3 CH3NO2 42 ZnCl2 CH3NO2 613 SnCl2 CH3NO2 514 Sc(OTf)3 CH3NO2 795 Yb(OTf)3 CH3NO2 756 Hf(OTf)4 CH3NO2 717 Ga(OTf)3 CH3NO2 698 Sb(OTf)3 CH3NO2 769 Sn(OTf)2 CH3NO2 86

10 Sn(OTf)2 CH3CN 6811 Sn(OTf)2 CH2Cl2 65

Table 2Acylation of furan

Entry R Yield (%)

1 Me 862 C5H11 983 i-Pr 954 t-Bu Quant.5 Ph 86

1022-5528/02/0300-0043/0 2002 Plenum Publishing Corporation

44 I. Komoto et al. / Catalytic Friedel–Crafts acylation

(1/2 = 85/15). We then screened several Lewis acids, and itwas found that stronger Lewis acids such as Ga(OTf)3 andHf(OTf)4 afforded the desired ketones in 59 and 46% yields,respectively (table 4). The best yield (72%) was obtainedusing Sc(OTf)3 as the Lewis acid catalyst, albeit the mixtureof 1 and2 was obtained (1/2 = 82/18).

In the acetylation of 1-(phenylsulfonyl)pyrrole, it was re-ported that 2-acetylated adduct (3) was obtained selectivelyusing 6 equiv. of BF3·OEt2, while 3-acylated adduct (4)was preferentially produced using 6 equiv. of AlCl3 [5f].Adduct4 was also obtained selectively when SnCl4, ZnCl2,TiCl4, or FeCl3 was employed. We examined the same re-action using a catalytic amount of a Lewis acid. SeveralLewis acids were examined and the results were summa-rized in table 5. When a catalytic amount of La(OTf)3,Y(OTf)3, Yb(OTf)3, Sc(OTf)3, Hf(OTf)4, or Ga(OTf)3 wasused, the reaction proceeded smoothly to afford the desired2-acylated adduct in high yields with high regioselectivity.Among Lewis acids tested, Ga(OTf)3 [8] gave the best resultin this case. It is noted that the acetylation also proceeded

Table 3Acetylation of thiophene

Entry Lewis acid Yield (%)

1 Sc(OTf)3 872 Sn(OTf)2 95

smoothly even when only 0.1 mol% of Ga(OTf)3 was em-ployed. Other acylating agents were tested, and in all casesthe desired acylated pyrroles were obtained in high yields inthe presence of a catalytic amount of Ga(OTf)3 (table 5). Inaddition, Ga(OTf)3 was also effective for the acetylation ofan indole derivative, and the 3-acetylated indole derivativewas obtained exclusively in high yield (equation (1))

(1)

Table 4Acetylation of 2,3-benzofuran

Entry Lewis acid Solvent Yield (%) 1/2

1 Sn(OTf)2 CH3NO2 30 85/152 Sb(OTf)3 CH3NO2 48 85/153 Ga(OTf)3 CH3NO2 59 86/144 Hf(OTf)4 CH3NO2 46 80/205 Yb(OTf)3 CH3NO2 57 85/156 Sc(OTf)3 CH3NO2 72 82/187 Sc(OTf)3 CH3CN 38 77/238 Sc(OTf)3 CH2Cl2 36 81/19

Table 5Friedel–Crafts acylation of 1-(phenylsulfonyl)pyrrole

Entry Lewis acid (mol%) X R1 R2 Condition Yield (%) 3 : 4a

1 La(OTf)3 (10) SO2Ph Me OAc rt, 56 h 60 86 : 142 Y(OTf)3 (10) SO2Ph Me OAc rt, 56 h 85 87 : 133 Yb(OTf)3 (10) SO2Ph Me OAc rt, 13 h 93 88 : 124 Sc(OTf)3 (10) SO2Ph Me OAc rt, 1 h 98 83 : 175 Hf(OTf)4 (10) SO2Ph Me OAc rt, 10 min 98 90 : 106 Ga(OTf)3 (10) SO2Ph Me OAc rt, 10 min 99 92 : 87 Ga(OTf)3 (1) SO2Ph Me OAc 0◦C, 18 h 97 97 : 38 Ga(OTf)3 (1) SO2Ph i-Pr OCOi-Pr 0◦C, 3 h Quant 90 : 109 Ga(OTf)3 (10) SO2Ph t-Bu OCOt-Bu rt, 18 h 94 6 : 94

10 Ga(OTf)3 (1) SO2Ph C5H11 OCOC5H11 0◦C, 23 h Quant 90 : 1011 Ga(OTf)3 (1) SO2Ph Me Cl rt, 22 h 85 95 : 512 Ga(OTf)3 (1) SO2Ph Pr Cl 0◦C, 23 h 84 85 : 15

then rt, 21 h13b Ga(OTf)3 (1) SO2Ph Ph Cl rt, 44 h 75 92 : 814 Yb(OTf)3 (10) SitBuMe2 Me OAc rt, 16 h 79 46 : 54c

15 Yb(OTf)3 (10) SiiPr3 Me OAc rt, 24 h 79 27 : 73c

aDetermined by NMR analysis.b Acylating agent (1.2 eq.) was used.c 3 was obtained as 2-acetylpyrrole.

I. Komoto et al. / Catalytic Friedel–Crafts acylation 45

In summary, catalytic Friedel–Crafts acylation of het-eroaromatics has been developed. Metal triflates were foundto be efficient catalysts for the acylation. Optimized metalsdepend on heteroaromatics; Sn(OTf)2 was an effective cat-alyst in the acylation of furan and thiophene, and Sc(OTf)3for 2,3-benzofuran, while Ga(OTf)3 gave the best result inthe acylation of 1-(phenylsulfonyl)pyrrole and 1-(phenyl-sulfonyl)indole.

3. Experimental

Melting points are uncorrected. IR spectra were recordedon a JASCO FT/IR-610.1H and 13C NMR spectra wererecorded on a Jeol JNM-LA300 or a JNM-LA400 spectrom-eter. Tetramethylsilane (TMS) served as an internal stan-dard (δ = 0.00) for 1H NMR, and CDCl3 (δ = 77.0) for13C NMR. All reactions were carried out under argon inflame-dried glassware. All the solvents used were purifiedaccording to standard procedures and dried over MS 4A or3A. Preparative TLC was performed on Wakogel B5F.

3.1. Typical experimental procedure for catalyticFriedel–Crafts acylation of furan

To a stirred solution of furan (124 mg, 1.83 mmol), aceticanhydride (375 mg, 3.68 mmol) in nitromethane (1.8 ml)was added Sn(OTf)2 (38 mg, 0.092 mmol) in one portion,and the mixture was stirred at room temperature for 4 h.After adding saturated aqueous NaHCO3 (10 ml), the mix-ture was extracted with Et2O (20 ml× 2). The combinedorganic extracts were dried over anhydrous Na2SO4 andthen filtered. The yield of 2-acetylfuran was determined byGC analysis. The mixture was evaporated to give a crudeoil, which was purified by preparative TLC to afford 2-acetylfuran [5a]. A pale yellow oil:1H NMR (300 MHz,CDCl3) δ 7.59 (dd,J = 1.7, 0.8 Hz, 1H), 7.19 (dd,J = 3.7,0.8 Hz, 1H), 6.54 (ddd,J = 3.7, 1.7, 0.8 Hz, 1H), 2.49(s, 3H);13C NMR (75 MHz, CDCl3) δ 186.8, 152.9, 146.4,117.2, 112.2, 26.0. IR (cm−1) (neat) 1678.

The 3-acetylated isomer was not observed by the NMRanalysis of the crude product.

3.2. Physical data of other acylation adducts

3.2.1. 2-acetylbenzofuranA white solid: Mp 72–73◦C (lit. [5c] 75–76◦C).1H NMR

(300 MHz, CDCl3) δ 7.72 (ddd,J = 7.9, 1.3, 0.9 Hz,1H), 7.59 (dddd,J = 8.4, 1.1, 0.9, 0.9 Hz, 1H), 7.51(d, J = 0.9 Hz, 1H), 7.49 (ddd,J = 8.4, 7.1, 1.3 Hz,1H), 7.32 (ddd,J = 7.9, 7.1, 1.1 Hz, 1H), 2.62 (s, 3H);13C NMR (75 MHz, CDCl3) δ 188.7, 155.7, 152.6, 128.3,127.0, 123.9, 123.3, 113.1, 112.5, 26.5. IR (cm−1) (KBr)1676.

3.2.2. 3-acetylbenzofuran [9]A pale yellow oil: 1H NMR (400 MHz, CDCl3) δ 8.21–

8.28 (m, 2H), 7.50–7.61 (m, 1H), 7.35–7.43 (m, 2H), 2.57

(s, 3H);13C NMR (75 MHz, CDCl3) δ 192.9, 158.5, 151.2,125.6, 124.5, 124.2, 122.8, 122.6, 111.4, 28.0. IR (cm−1)(KBr) 1673.

3.2.3. 2-isobutyrylfuran [10]A pale yellow oil: 1H NMR (300 MHz, CDCl3) δ 7.59

(dd,J = 1.7, 0.7 Hz, 1H), 7.20 (dd,J = 3.5, 0.7 Hz, 1H),6.53 (dd,J = 3.5, 1.7 Hz, 1H), 3.34 (Sept,J = 6.9 Hz,1H), 1.21 (d,J = 6.8 Hz, 7H);13C NMR (75 MHz, CDCl3)δ 193.6, 152.1, 146.2, 117.1, 112.1, 36.2, 18.8. IR (cm−1)(neat) 1675.

3.2.4. 2-pivaloylfuran [11]A pale yellow oil: 1H NMR (300 MHz, CDCl3) δ 7.54

(dd,J = 1.8, 0.7 Hz, 1H), 7.21 (dd,J = 3.7, 0.7 Hz, 1H),6.50 (dd,J = 3.7, 1.8 Hz, 1H), 1.35 (s, 1H);13C NMR(75 MHz, CDCl3) δ 194.9, 152.5, 144.9, 118.0, 111.7, 43.0,26.8. IR (cm−1) (neat) 1666.

3.2.5. 2-hexanoylfuran [12]A pale yellow oil: 1H NMR (300 MHz, CDCl3) δ 7.58

(dd,J = 1.7, 0.8 Hz, 1H), 7.18 (dd,J = 3.6, 0.8 Hz, 1H),6.53 (dd,J = 3.6, 1.7 Hz, 1H), 2.81 (t,J = 7.5 Hz, 2H),1.66–1.79 (m, 2H), 1.27–1.42 (m, 4H), 0.84–0.96 (m, 3H);13C NMR (75 MHz, CDCl3) δ 189.9, 152.8, 146.1, 116.8,112.1, 38.5, 31.5, 24.0, 22.4, 13.9. IR (cm−1) (neat) 1677.

3.2.6. 2-benzoylfuran [13]A colorless oil:1H NMR (300 MHz, CDCl3) δ 7.94–8.02

(m, 2H), 7.71 (dd,J = 1.7, 0.7 Hz, 1H), 7.56–7.63 (m, 1H),7.46–7.54 (m, 2H), 7.24 (dd,J = 3.5, 0.7 Hz, 1H), 6.60 (dd,J = 3.5, 1.7 Hz, 1H);13C NMR (75 MHz, CDCl3) δ 182.5,152.2, 147.1, 137.2, 132.5, 129.2, 128.4, 120.6, 112.2. IR(cm−1) (neat) 1647.

3.2.7. 2-acetylthiophene [5a]A yellow oil: 1H NMR (300 MHz, CDCl3) δ 7.71 (dd,

J = 4.0, 1.0 Hz, 1H), 7.64 (dd,J = 5.0, 1.0 Hz, 1H), 7.14(dd,J = 5.0, 4.0 Hz, 1H), 2.58 (s, 3H);13C NMR (75 MHz,CDCl3) δ 190.8, 144.6, 133.8, 132.4, 128.1, 26.9. IR (cm−1)(neat) 1660.

3.2.8. 1-phenylsulfonyl-2-acetylpyrroleA white solid: Mp 96–97◦C (lit. [5f] 96–98◦C).1H NMR

(300 MHz, CDCl3) δ 8.00–8.03 (m, 1H), 7.96–8.00 (m, 1H),7.83 (dd,J = 3.2, 1.7 Hz, 1H), 7.57–7.64 (m, 1H), 7.48–7.56 (m, 2H), 7.06 (dd,J = 3.4, 1.7 Hz, 1H), 6.36 (dd,J = 3.4, 3.2 Hz, 1H), 2.35 (s, 3H);13C NMR (75 MHz,CDCl3) δ 185.7, 138.9, 133.6, 133.3, 130.4, 128.6, 1, 128.1,124.4, 110.4, 26.9. IR (cm−1) (KBr) 1678.

3.2.9. 1-phenylsulfonyl-3-acetylpyrroleA pale brown solid: Mp 98–99◦C (lit. [5f] 97–99◦C).

1H NMR (300 MHz, CDCl3) δ 7.93–7.96 (m, 1H), 7.90–7.93 (m, 1H), 7.75 (dd,J = 2.2, 1.7 Hz, 1H), 7.64–7.70(m, 1H), 7.52–7.60 (m, 2H), 7.16 (dd,J = 3.3, 2.2 Hz,1H), 6.69 (dd,J = 3.3, 1.7 Hz, 1H), 2.41 (s, 3H);13C NMR

46 I. Komoto et al. / Catalytic Friedel–Crafts acylation

(75 MHz, CDCl3) δ 192.8, 138.0, 134.6, 129.7, 129.4, 127.1,124.5, 121.6, 112.4, 27.2. IR (cm−1) (KBr) 1668.

3.2.10. 1-phenylsulfonyl-2-butyrylpyrroleA pale yellow oil: 1H NMR (300 MHz, CDCl3) δ 7.98–

8.02 (m, 2H), 7.81 (dd,J = 3.3, 1.7 Hz, 1H), 7.48–7.62(m, 3H), 7.04 (dd,J = 3.8, 1.7 Hz, 1H), 6.34 (dd,J = 3.8,3.3 Hz, 1H), 2.64 (t,J = 7.4 Hz, 2H), 1.62 (tq,J = 7.4,7.4 Hz, 2H), 0.87 (t,J = 7.4 Hz, 3H);13C NMR (100 MHz,CDCl3) δ 188.9, 139.1, 133.5, 130.0, 128.7, 128.1, 123.2,110.3, 41.2, 18.3, 13.7. IR (cm−1) (neat) 1679. Anal.calcd. for C14H15NO3S: C, 60.63; H, 5.45; N, 5.05. Found:C, 60.49; H, 5.47; N, 5.06.

3.2.11. 1-phenylsulfonyl-3-butyrylpyrroleA pale yellow oil: 1H NMR (400 MHz, CDCl3) δ 7.89–

7.94 (m, 2H), 7.74 (t,J = 1.9 Hz, 1H), 7.48–7.68 (m, 3H),7.15 (dd,J = 3.3, 2.2 Hz, 1H), 6.69 (dd,J = 3.3, 1.5 Hz,1H), 2.70 (t,J = 7.4 Hz, 2H), 1.70 (tq,J = 7.4, 7.4 Hz,2H), 0.95 (t,J = 7.4 Hz, 3H);13C NMR (100 MHz, CDCl3)δ 195.5, 138.2, 134.5, 133.1, 129.7, 129.3, 127.6, 127.1,124.1, 121.5, 112.5, 41.6, 17.7, 13.8. IR (cm−1) (neat) 1676.Anal. calcd. for C14H15NO3S: C, 60.63; H, 5.45; N, 5.05.Found: C, 60.54; H, 5.39; N, 4.75.

3.2.12. 1-phenylsulfonyl-2-isobutyrylpyrroleA pale yellow oil: 1H NMR (300 MHz, CDCl3) δ 7.96–

8.02 (m, 2H), 7.80 (dd,J = 3.2, 1.7 Hz, 1H), 7.48–7.64 (m, 3H), 7.02 (dd,J = 3.7, 1.7 Hz, 1H), 6.35 (dd,J = 3.7, 3.2 Hz, 1H), 3.16 (sept,J = 6.9 Hz, 1H), 1.08(d,J = 6.9 Hz, 6H);13C NMR (100 MHz, CDCl3) δ 199.6,139.1, 133.5, 133.0, 130.0, 128.7, 128.0, 122.4, 110.4, 37.4,19.1. IR (cm−1) (neat) 1677. Anal. calcd. for C14H15NO3S:C, 60.63; H, 5.45; N, 5.05. Found: C, 60.47; H, 5.46;N, 4.95.

3.2.13. 1-phenylsulfonyl-3-isobutyrylpyrroleA pale yellow oil: 1H NMR (300 MHz, CDCl3) δ 7.88–

7.94 (m, 2H), 7.75 (dd,J = 2.3, 1.7 Hz, 1H), 7.48–7.68 (m, 3H), 7.15 (dd,J = 3.2, 2.3 Hz, 1H), 6.70 (dd,J = 3.2, 1.7 Hz, 1H), 3.15 (sept,J = 6.9 Hz, 1H), 1.16(d,J = 6.9 Hz, 6H);13C NMR (100 MHz, CDCl3) δ 199.7,138.2, 134.5, 129.7, 128.1, 127.1, 124.1, 121.6, 112.9, 37.4,19.1. IR (cm−1) (neat) 1672. Anal. calcd. for C14H15NO3S:C, 60.63; H, 5.45; N, 5.05. Found: C, 60.58; H, 5.60;N, 4.89.

3.2.14. 1-phenylsulfonyl-2-hexanoylpyrroleA pale yellow oil: 1H NMR (400 MHz, CDCl3) δ 7.97–

8.03 (m, 2H), 7.80 (dd,J = 3.2, 1.7 Hz, 1H), 7.49–7.63(m, 3H), 7.03 (dd,J = 3.7, 1.7 Hz, 1H), 6.34 (dd,J = 3.7,3.2 Hz, 1H), 2.65 (t,J = 7.6 Hz, 2H), 1.52–1.68 (m, 2H),1.17–1.36 (m, 4H), 0.85 (t,J = 7.0 Hz, 3H); 13C NMR(100 MHz, CDCl3) δ 189.1, 39.1, 133.5, 130.0, 128.7, 128.1,123.2, 110.3, 39.4, 31.3, 24.6, 22.4, 13.9. IR (cm−1) (neat)1677. Anal. calcd. for C16H19NO3S: C, 62.93; H, 6.27;N, 4.59. Found: C, 62.84; H, 6.20; N, 4.55.

3.2.15. 1-phenylsulfonyl-3-hexanoylpyrrole [5m]A pale yellow oil: 1H NMR (400 MHz, CDCl3) δ 7.89–

7.94 (m, 2H), 7.72–7.74 (m, 1H), 7.63–7.69 (m, 1H), 7.53–7.58 (m, 2H), 7.14 (dd,J = 3.4, 2.2 Hz, 1H), 6.69 (dd,J = 3.4, 1.7 Hz, 1H), 2.71 (t,J = 7.4 Hz, 2H), 1.60–1.72 (m, 2H), 1.26–1.40 (m, 4H), 0.89 (t,J = 7.0 Hz, 3H);13C NMR (100 MHz, CDCl3) δ 195.7, 138.2, 134.5, 129.7,129.3, 127.1, 124.1, 121.6, 112.6, 39.8, 31.5, 24.0, 22.5,13.9. IR (cm−1) (neat) 1676.

3.2.16. 1-phenylsulfonyl-2-pivaloylpyrroleA colorless oil:1H NMR (400 MHz, CDCl3) δ 7.97–8.01

(m, 2H), 7.51–7.64 (m, 4H), 6.75 (dd,J = 3.6, 1.5 Hz, 1H),6.28 (t,J = 3.6 Hz, 1H), 1.28 (s, 9H);13C NMR (100 MHz,CDCl3) δ 199.5, 139.5, 133.6, 132.4, 128.8, 127.9, 126.7,118.3, 110.5, 44.2, 27.7. IR (cm−1) (neat) 1667. Anal.calcd. for C15H17NO3S: C, 61.83; H, 5.88; N, 4.81. Found:C, 61.62; H, 5.96; N, 4.76.

3.2.17. 1-phenylsulfonyl-3-pivaloylpyrrole [5m]A pale yellow oil: 1H NMR (400 MHz, CDCl3) δ 7.89–

7.92 (m, 2H), 7.74 (dd,J = 2.2, 1.7 Hz, 1H), 7.63–7.68(m, 1H), 7.52–7.58 (m, 2H), 7.11 (dd,J = 3.4, 2.2 Hz, 1H),6.72 (dd,J = 3.4, 1.7 Hz, 1H), 1.29 (s, 9H);13C NMR(100 MHz, CDCl3) δ 201.2, 138.3, 134.5, 129.7, 127.1,126.3, 124.3, 120.5, 114.4, 43.9, 27.7. IR (cm−1) (neat)1665.

3.2.18. 1-phenylsulfonyl-2-benzoylpyrroleA colorless solid: Mp 141–143◦C (lit. [5f] 134–136◦C).

1H NMR (400 MHz, CDCl3) δ 8.11–8.15 (m, 2H), 7.78–7.82 (m, 3H), 7.66–7.67 (m, 1H), 7.53–7.62 (m, 3H), 7.44(t, J = 7.7 Hz, 2H), 6.73 (dd,J = 3.6, 1.7 Hz, 1H), 6.36(t, J = 3.6 Hz, 1H);13C NMR (100 MHz, CDCl3) δ 184.4,139.3, 137.8, 133.8, 133.7, 133.2, 132.7, 130.2, 129.7,129.5, 129.3, 128.8, 128.5, 128.3, 128.2, 125.2, 110.1. IR(cm−1) (KBr) 1688.

3.2.19. 1-phenylsulfonyl-3-benzoylpyrroleA white solid: Mp 65–67◦C (lit. [5f] 69–72◦C).1H NMR

(400 MHz, CDCl3) δ 7.88–7.93 (m, 2H), 7.79–7.84 (m, 2H),7.43–7.69 (m, 7H), 7.22 (dd,J = 3.2, 2.2 Hz, 1H), 6.82(dd, J = 3.2, 1.6 Hz, 1H);13C NMR (75 MHz, CDCl3)δ 189.9, 138.2, 134.6, 132.4, 129.7, 129.1, 129.0, 128.5,128.0, 127.2, 126.1, 121.5, 114.2. IR (cm−1) (KBr) 1688.

3.2.20. 1-t-butyldimethylsilyl-3-acetylpyrrole [5h]A brown oil: 1H NMR (300 MHz, CDCl3) δ 7.38 (t,J =

1.7 Hz, 1H), 6.68–6.74 (m, 2H), 2.42 (s, 3H), 0.90 (s, 9H),0.46 (s, 6H);13C NMR (75 MHz, CDCl3) δ 193.8, 129.3,128.4, 125.2, 110.9, 27.3, 25.6, 17.8,−5.7. IR (cm−1) (neat)1664.

3.2.21. 2-acetylpyrroleA yellow solid: Mp 84–87◦C (lit. [14] 90◦C). 1H NMR

(300 MHz, CDCl3) δ 10.03 (bs, 1H), 7.04–7.07 (m, 1H),6.91–6.94 (m, 1H), 6.26–6.29 (m, 1H), 2.44 (s, 3H);

I. Komoto et al. / Catalytic Friedel–Crafts acylation 47

13C NMR (75 MHz, CDCl3) δ 188.2, 132.1, 124.9, 117.0,110.5, 25.4. IR (cm−1) (KBr) 1647.

3.2.22. 1-triisopropylsilyl-3-acetylpyrroleA yellow solid: Mp 67–69◦C (lit. [5l] 69 ◦C). 1H NMR

(400 MHz, CDCl3) δ 7.40 (bs, 1H), 6.70–6.75 (m, 2H), 2.43(s, 3H), 1.48 (sept,J = 7.4 Hz, 3H), 1.11 (d,J = 7.4 Hz,18H); 13C NMR (100 MHz, CDCl3) δ 193.8, 129.4, 128.3,125.4, 110.8, 27.3, 17.5, 11.4. IR (cm−1) (KBr) 1651.

3.2.23. 1-phenylsulfonyl-3-acetylindoleA colorless solid: Mp 147◦C (lit. [5k] 155–157◦C).

1H NMR (400 MHz, CDCl3) δ 8.31–8.35 (m, 1H), 8.24(s, 1H), 7.92–7.98 (m, 3H), 7.57 (t,J = 7.8 Hz, 1H),7.47 (t,J = 7.8 Hz, 2H), 7.30–7.39 (m, 2H), 2.57 (s, 3H);13C NMR (100 MHz, CDCl3) δ 193.4, 137.3, 134.8, 134.5,132.1, 129.5, 127.4, 127.0, 125.7, 124.8, 123.0, 121.6,112.9, 27.7. IR (cm−1) (KBr) 1664.

Acknowledgement

This work was partially supported by a Grant-in-Aid forScientific Research from the Ministry of Education, Science,Sport, and Culture, Japan.

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