Iodine - catalyzed prins cyclization of aliphatic and aromatic ketones

ARTICLE

Iodine-catalyzed prins cyclization of aliphatic and aromatic ketones

K. R. Kishore K. Reddy; Luiz F. Silva Jr^*

Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, CP 26077, 05513-970 São Paulo-SP, Brazil

ABSTRACT

Iodine-catalyzed Prins cyclization of homoallylic alcohols and ketones was investigated. Anhydrous conditions and inert atmosphere are not required in this metal-free protocol. The reaction of 2-(3,4-dihydronaphthalen-1-yl)propan-1-ol with six aliphatic symmetric ketones gave the desired products in 67-77% yield. Cyclization was performed with four aliphatic unsymmetric ketones, leading to corresponding pyrans in 66-76% yield. Prins cyclization was also accomplished with four aromatic ketones in 37-66% yield. Finally, Prins cyclization of the monoterpene isopulegol and acetone was successfully achieved.

Keywords: iodine, Prins cyclization, ketones, pyrans, spiro compounds

RESUMO

A ciclização de Prins catalisada por iodo entre álcoois homoalílicos e cetonas foi investigada. Condições anidras e atmosfera inerte não são necessárias neste protocolo ausente de metais. A reação do 2-(3,4-di-hidronaftalen-1-il)propan-1-ol com seis cetonas simétricas alifáticas levou ao produto desejado em 67-77% de rendimento.A ciclização foi realizada com quatro cetonas alifáticas assimétricas, levando aos correspondentes piranos em 66-76% de rendimento. A ciclização de Prins também foi alcançada com quatro cetonas aromáticas com 37-66% de rendimento. Finalmente, a ciclização de Prins do monoterpeno isopulegol e acetona foi realizada com sucesso.

Introduction

Prins cyclization constitutes a powerful tool to obtain tetrahydropyrans (Scheme 1),^1-3 including the key step in several total syntheses.^4-14 Typically, Prins cyclization is performed mixing a homoallylic alcohol and an aldehyde in the presence of excess of an acid under anhydrous conditions. The use of ketones as the carbonyl components is restricted to a relatively small number of examples.^15-22 Additionally, only aliphatic symmetric ketones were usually employed. Herein, we describe the Prins cyclization of homoallylic alcohols 1a-b (Figure 1) with several ketones (aliphatic and aromatic, symmetric and non symmetric) catalyzed by 5 mol% of iodine^23,24 without using anhydrous conditions and inert atmosphere.^25-27

Results and Discussion

We start our study investigating the reaction of the readily available homoallylic alcohol 1a²⁸ with 1 equiv of acetone (2a) in CH2Cl2. The desired Prins cyclization product 3a was obtained in 76% yield using 5 mol% of iodine (Table 1, entry 1). Under similar conditions, the Prins cyclization could also be performed with 2-pentanone (2b, entry 2), as well as with a series of cyclic ketones (2c-f, entries 3-6).

The next step was the study of unsymmetrical ketones (Table 2). The iodine-catalyzed Prins cyclization of 1a with ketone 2g gave the chromene derivative 3g in 71% isolated yield, as a 1:1.25 mixture of diastereomers (entry 1). A similar result was obtained using the ketone 2h, although in a slightly higher diastereoselectivity (entry 2).

Ethyl acetoacetate (2i) was also used as the carbonyl component, giving 3i in 75% yield (entry 3). In such a case, the diastereoselectivity was higher than using 2g-h. The reaction of 1a with menthone 2j gave the spirocyclic compound 3j in 22% yield, as a single diastereomer. This low yield is analogous to that previously reported for Prins cyclizations using menthone.²²

Considering the results obtained with aliphatic ketones, we tuned our attention to the less reactive aromatic ketones (Table 3). The coupling of acetophenone (2k) and 1a gave 3k, as a 1:5 mixture of diastereomers in 66% yield (entry 1). Using benzophenone (2l) as the carbonyl component, the desired product 3l was isolated in 43% yield (entry 2). The spirocyclic compound 3m was obtained in 52% yield as a single diastereomer, using 1-tetralone (2m), as substrate (entry 3). Chromanone 2n gave the spiro cyclic compound 3n in 37% yield (entry 4).

Based on the results in Tables 1-3, it is possible to conclude that lower yields were observed for the more bulky ketones, either aliphatic (Table 2, entry 4) or aromatic (Table 3, entries 2-4). Additionally, the relative configuration of the Prins cyclization products (3g-k and 3m-n ) shows that the bulkier group is cis to the methyl group. This agrees with the mechanism proposed for the iodine-catalyzed Prins cyclization.²⁵ The relative configurations were assigned by nuclear magnetic resonance (NMR) analysis, including Overhauser effect spectroscopy (NOESY) experiments.

The Prins cyclization of the monoterpene isopulegol 1b was also investigated, because it has very different structural features when compared to 1a. Treatment of a mixture of 1b and acetone (2a) with iodine gave the functionalized bicyclic compound 5, as a single diastereoisomer. It is important to note that in this case the carbocation intermediate 4 reacts with water (formed in situ), instead of losing a proton like in previous cases. The attack of water occurs through the equatorial face, explaining the formation of a single diastereoisomer (Scheme 2).^25,29

Conclusions

The iodine-catalyzed Prins cyclization of homoallylic alcohols and several ketones (aliphatic and aromatic, symmetric and unsymmetric) furnishes the desired hydropyrans in good to moderate yield. This protocol can be useful to prepare O-heterocycles under very mild conditions. In the case of hindered ketones, the desired products were obtained in lower yield.

Experimental

All commercially available reagents were used without further purification unless otherwise noted. Commercially available isopulegol was purified by flash column chromatography (15% AcOEt in hexanes). Tetrahydrofuran (THF) and benzene were freshly distilled from sodium/ benzophenone. CH₂Cl₂ was freshly distilled over CaH₂. Thin layer chromatography (TLC) analyses were performed in silica gel plates, using UV and/or p-anisaldehyde solution for visualization. Flash column chromatography was performed using silica gel 200-400 mesh. Melting points are uncorrected. All NMR analyses were recorded using CDCl₃ as solvent and tetramethylsilane (TMS) as internal pattern. The experimental procedures for the preparation of compounds 3a and 3c-e were previously reported.²⁵

4,4-Diethyl-1-methyl-1,4,5,6-tetrahydro-2H-benzo[f] isochromene (3b). General procedure for iodine-catalyzed prins cyclization: I₂ (0.030, 0.076 mmol) was added to a stirred solution of 1a (0.113 g, 0.600 mmol) and 2b (0.06 mL, 0.6 mmol) in CH₂Cl₂ (5 mL). The mixture was refluxed for 3 h. Na₂SO₃ (0.0075 g, 0.60 mmol) and H₂O (10 mL) were added. The aqueous phase was extracted with AcOEt (3 × 5 mL). The combined organic phase was washed with brine (5 mL) and dried over anhydrous MgSO₄. The solvent was removed under reduced pressure. The crude product was purified by flash column chromatography (5% AcOEt in hexanes), affording 3b (0.115 g, 0.450 mmol, 75%) as white solid; mp 58-60 ºC; R_f = 0.56 (hexanes:EtOAc, 9:1); IR (film) ν/cm^-1 3061, 2963, 2930, 1487, 1452, 765, 733; ¹H NMR (200 MHz, CDCl₃) δ 0.91 (t, J 7.4 Hz, 3H), 1.25 (d, J 6.8 Hz, 3H), 1.47-162 (m, 2H), 1.71-1.85 (m, 2H), 2.06-2.13 (m, 2H), 2.56-2.64(m, 1H), 2.69-2.79 (m, 2H), 3.62 (dd, J 11.2, 1.7 Hz, 1H), 3.90 (dd, J 11.1, 3.2 Hz, 1H), 7.10-7.14 (m, 2H), 7.16-7.28 (m, 2H); ¹³C NMR (50 MHz, CDCl₃) δ 7.4, 8.7, 18.6, 24.1, 28.0, 28.5, 28.6, 28.7, 65.3, 79.6, 122.2, 126.2, 126.4, 127.4, 131.4, 134.1, 136.0, 136.9; LRMS m/z (rel. int.) 256 (M^+•, 0.32), 228 (10), 227 (100); HRMS [ESI(+)] calcd. for [C₁₈H₂₄O + Na]⁺ 279.1725, found 279.1718.

1-Methyl-1,2,5,6-tetrahydrospiro[benzo[f ]isochromene-4,1'-cyclododecane] (3f): the reaction was performed following the general procedure, but using 1a (0.113 g, 0.600 mmol), 2f (0.110 g, 0.600 mmol), CH₂Cl₂ (5 mL) and I₂ (0.0076, 0.030 mmol). Compound 3f (0.148 g, 0.420 mmol, 70%) was obtained as colorless oil; R_f = 0.76 (hexanes-EtOAc, 9.5:0.5); IR (film) ν/cm^-1 3063, 2926, 2932, 2861, 1469, 765, 733; ¹H NMR (200 MHz,CDCl₃) δ 1.21 (d, J 6.8 Hz, 3H), 1.40-1.47 (m, 18H), 1.69-1.79 (m, 4H), 2.06-2.31 (m, 2H), 2.62-2.70 (m, 3H), 3.59 (dd, J 2.4, 11.0 Hz, 1H), 3.87 (dd, J 3.3, 11.1 Hz, 1H), 7.09-7.28 (m, 4H); ¹³C NMR (50 MHz, CDCl₃) δ 18.3, 20.2, 21.1, 22.8, 23.0, 23.3, 23.6, 24.7, 25.7, 27.0, 27.1, 28.7, 29.1, 31.6, 35.8, 65.2, 78.6, 122.4, 126.0, 126.3, 127.2, 130.0, 134.3, 136.0,139.5; LRMS m/z (rel. int.) 352 (M^+•, 27.0), 337 (7.3), 309 (4.36), 281 (6.0), 226 (16.8), 225 (100); HRMS [ESI(+)] calcd. for [C₂₅H₃₆O + H]⁺ 353.2839, found 353.2841.

2,4,5,6-Tetrahydro-4-isobutyl-1,4-dimethyl-1H-benzo[f ] isochromene (3g): the reaction was performed following the general procedure, but using 1a (0.090 g, 0.48 mmol), 2g (0.060 mL, 0.48 mmol), CH₂Cl₂ (5 mL) and I₂ (0.0061 g, 0.024 mmol). Compound 3g (1:1.25 cis:trans, 0.092 g, 0.34 mmol, 71%) was obtained as a pale yellow oil; R_f = 0.63 (hexanes-EtOAc, 9:1); IR (film) ν/cm^-1 3061, 2950, 2928, 1488, 1451, 1126, 766, 735; ¹H NMR (300 MHz, CDCl₃) δ trans-3g 0.95 (d, J 6.6 Hz, 6H), 1.18 (d, J 6.9 Hz, 3H), 1.39 (s, 3H), 1.42-1.71 (m, 2H), 1.80-1.90 (m, 1H), 2.04-2.16 (m, 2H), 2.67-2.78 (m, 3H), 3.58 (dd, J 11.1, 3.3 Hz, 1H), 3.91 (dd, J 11.4, 3.6 Hz, 1H), 7.11-7.13 (m, 2H), 7.15-7.29 (m, 2H); cis-3g 9.07 (d, J 6.6 Hz, 3H), 1.02 (d, J 6.6 Hz, 3H), 1.271 (s, 3H), 1.274 (d, J 6.9 Hz, 3H), 3.65 (dd, J 11.1, 1.5 Hz, 1H), 3.94 (dd, J 11.4, 3.0 Hz, 1H). Other signals overlap with the major diastereomer; ¹³C NMR (50 MHz, CDCl₃) δ trans-3g 18.0, 24.0, 24.1, 24.2, 24.8, 25.2, 28.8, 43.9, 65.6, 77.2, 122.5, 126.1, 126.3, 127.3, 130.1, 134.1, 136.0, 139.4; cis-3g 18.5, 24.1, 24.4, 24.7, 25.1, 25.6, 28.3, 48.4, 65.4, 78.1, 122.2, 126.2, 126.4, 127.4, 130.7, 135.7, 137.5 ; LRMS m/z (rel. int.) 270 (M^+• , 2.03), 255 (20), 214 (17), 213 (100); HRMS [ESI(+)] calcd. for [C₁₉H₂₆O + H]⁺ 271.2062, found 271.2053.

2,4,5,6-Tetrahydro-4-isopropyl-1,4-dimethyl1H-benzo[f ]isochromene (3h): the reaction was performed following the general procedure, but using 1a (0.113 g, 0.600 mmol), 2h (0.064 mL, 0.60 mmol), CH₂Cl₂ (5 mL) and I₂ (0.0076, 0.030 mmol). Compound cis-3h (0.0271, 0.106 mmol, 18%) and trans-3h (0.0675 g, 0.264 mmol, 44%) were obtained as white solid and colorless viscous oil, respectively. (±)-(1R,4R)-2,4,5,6-tetrahydro4-isopropyl-1,4-dimethyl-1H-benzo[f]isochromene (cis-3h); mp 61-63 ºC; R_f = 0.34 (hexanes-EtOAc, 9.5:0.5); IR (film) ν/cm^-1 3060, 2967, 2934, 1451, 766; ¹H NMR (300 MHz, CDCl₃) δ 0.84 (d, J 6.9 Hz, 3H), 1.03 (d, J 6.6 Hz, 3H), 1.09 (d, J 6.6 Hz, 3H), 1.40 (s, 3H), 1.86-1.95 (m, 1H), 2.07-2.15 (m, 2H), 2.61-2.80 (m, 2H), 2.82-2.84 (m, 1H), 3.58 (dd, J 11.2, 6.0 Hz, 1H), 3.99 (dd, J 11.1, 4.5 Hz, 1H), 7.11-7.15 (2H), 7.22-7.23 (m, 2H); ¹³C NMR (50 MHz, CDCl₃) δ 16.1, 17.1, 18.6, 24.5, 24.7, 28.6, 28.7, 34.4, 67.1, 78.3, 123.0, 125.9, 126.1, 127.1, 131.4, 134.2, 136.1, 139.4; LRMS m/z (rel. int.) 256 (M^+• , 0.08), 241 (0.87), 213 (100); HRMS [ESI(+)] calcd. for [C₁₈H₂₅O + H]⁺ 257.1900, found 257.1899. (±)-(1R,4S)-2,4,5,6-tetrahydro-4-isopropyl-1,4-dimethyl-1H-benzo[f] isochromen (trans-3h); R_f = 0.31 (hexanes-EtOAc, 9.5:0.5); IR (film) ν/cm^-1 3061, 2964, 2931, 1451, 766; ¹H NMR (300MHz, CDCl₃) δ 0.92 (d, J 6.8 Hz, 3H), 1.04 (d, J 6.8 Hz, 3H), 1.28 (d, J 7.0 Hz, 3H), 1.30 (s, 3H), 1.88-2.02 (m, 1H), 2.08-2.18 (m, 2H), 2.54-2.59 (m, 1H), 2.71-2.80 (m, 2H), 3.66 (dd, J 0.8, 11.0 Hz, 1H), 3.90 (dd, J 3.1, 11.1 Hz, 1H), 7.10-7.13 (m, 2H), 7.17-7.30 (m, 2H); ¹³C NMR (75 MHz, CDCl₃) δ 16.1, 18.47, 18.51, 21.2, 23.8, 28.5, 28.8, 34.6, 65.3, 78.6, 122.1, 126.2, 126.4, 127.4, 130.3, 134.2, 135.8, 138.1; LRMS m/z (rel. int.) 256 (M^+•, 0.5), 241 (4.1), 213 (100); HRMS [ESI(+)] calcd. for [C₁₈H₂₄O + Na]⁺ 279.1719, found 279.1679.

Ethyl 2-(2,4,5,6-tetrahydro-1,4-dimethyl-1H-benzo[f ] isochromen-4-yl)acetate (3i): the reaction was performed following the general procedure, but using 1a (0.89 g, 0.47 mmol), 2i (0.060 mL, 0.47 mmol), CH₂Cl₂ (5 mL) and I₂ (0.0060, 0.024 mmol). Compound 3i (1:4.8, cis:trans 0.108 g, 0.36 mmol, 76%) was obtained as colorless viscous oil; R_f = 0.26 ((hexanes-EtOAc, 9:1); IR (film) ν/cm^-1 3060, 2975, 2932, 2900, 2870, 1732, 1488, 1463, 1450, 1034, 1060, 1075, 768, 735. ¹H NMR (300 MHz, CDCl₃) δ trans-3i 1.75 (d, J 4.2 Hz, 3H), 1.20 (t, J 4.2 Hz, 3H), 1.39 (s, 3H), 2.13-2.28 (m, 2H), 2.63-2.66 (m, 1H), 2.66 (d, J 7.8 Hz, 1H), 2.69-2.74 (m, 1H), 2.79 (d, J 8.1 Hz, 3H), 2.85-2.94 (m, 1H), 3.70 (dd, J 6.75, 1.0 Hz, 1H), 3.92 (dd, J 6.9, 1.8 Hz, 3H), 4.09 (q, J 4.2 Hz, 2H), 7.12-7.13 (m, 2H), 7.18-7.22 (m, 1H), 7.24 (br, 1H). cis-3i 1.23 (d, J 3.9 Hz, 3H), 1.24 (d, J 4.2 Hz, 3H), 1.54 (s, 3H), 4.15 (d, J 4.2 Hz, 2H) 7.14 -7.15 (m, 2H). Other signals overlap with the major diastereomer; ¹³C NMR (50 MHz, CDCl₃) δ trans-3i 14.2, 18.0, 23.3, 24.6, 28.1, 28.5, 45.4, 45.4, 60.3, 65.6, 77.2, 122.3, 126.3, 126.5, 127.5, 131.1, 133.7, 135.6, 136.1, 170.2, cis-3i 13.9, 18.1, 24.3, 25.9, 28.5, 28.7, 41.8, 60.4, 66.0, 75.7, 122.5, 125.4, 126.6, 128.6, 130.9, 134.0, 135.8, 136.7, 170.5; LRMS m/z (rel. int.) 300 (M^+• , 2.3), 213 (60.8), 165 (16.0), 153 (17.4), 141 (23.0), 128 (22.5), 115 (19.9), 43 (100); HRMS [ESI(+)] calcd. for C₁₉,H₂₄O₃+Na]⁺ 323.1623, found.323.1625.

(1R,2'R,5'R)-2'-isopropyl-1,5-diMethyl-1,2,5,6-etrahydrospiro[benzo[f ]issochrom-ene-4,1'cyclohexane] (3j): the reaction was performed following the general procedure, but using 1a (0.113 g, 0.600 mmol), 2j (0.103 mL, 0.600 mmol), CH₂Cl₂ (5 mL) and I₂ (0.0076, 0.030 mmol). Compound 3j (0.0429 g, 0.132 mmol, 22%) was obtained as colorless oil; R_f = 0.41 (hexanes-EtOAc, 9.5:0.5); IR (film) ν/cm^-1 3061, 3030, 2936, 2924, 2856, 1453, 1090, 748, 699; ¹H NMR (300 MHz, CDCl₃) δ 0.77 (d, J 7.2 Hz, 3H), 0.85 (d, J 6.8 Hz, 3H), 0.90 (d, J 6.4 Hz, 3H), 0.99 (d, J 6.8 Hz, 3H), 1.13-1.29 (m, 2H), 1.32-1.37 (m, 1H), 1.42-1.68 (m, 4H), 1.75-1.82 (m, 2H), 1.91-2.05 (m, 2H), 2.12-2.20 (m, 1H), 2.55-2.73 (m, 2H), 2.90-2.97 (m, 1H), 3.48 (dd, J 11.4, 8.4 Hz, 1H), 3.92 (dd, J 11.4, 5.7 Hz, 1H), 7.12-7.15 (m, 2H), 7.21-7.23 (m, 2H); ¹³C NMR (50 MHz, CDCl₃) δ 16.8, 18.7, 20.5, 22.5, 24.0, 24.7, 27.2, 27.5, 28.3, 28.8, 35.3, 42.4, 46.1, 65.5, 80.0, 123.5, 125.7, 125.9, 127.0, 132.4, 134.5, 136.4, 140.2; LRMS m/z (rel. int.) 324 (M^+•, 10), 309 (3.37), 240 (17), 239 (100); HRMS [ESI(+)] calcd. for [C₂₃H₃₂O + H]⁺325.2526, found 325.2532.

1,4-Dimethyl-4-phenyl-1,4,5,6-tetrahydro-2H-benzo[f ] isochromene (3k): the reaction was performed following the general procedure, but using 1a (0.113 g, 0.600 mmol), 2k (0.070 mL, 0.60 mmol), CH₂Cl₂ (5 mL) and I₂ (0.0076, 0.030 mmol). The crude product was purified by flash column chromatography (2% AcOEt in hexanes). Compounds cis-3k (0.0186 g, 0.0641 mmol, 11%) as a white solid and trans-3k (0.097 g, 0.33 mmol, 55%) as colorless viscous oil were obtained. (±)-(1R,4R)1,4-dimethyl-4-phenyl-1,4,5,6-tetrahydro-2H-benzo[f] isochromene (cis-3k); mp 98-100 ºC; R_f = 0.38 (hexanes-EtOAc, 9.5:0.5); IR (film) ν/cm^-1 3059, 2929, 2247, 1489, 764, 699; ¹H NMR (200 MHz, CDCl₃) δ 1.35 (d, J 6.8 Hz, 3H), 1.80 (s, 3H), 1.94-2.10 (m, 1H), 2.19-2.35 (m, 1H), 2.65-2.70 (m, 1H), 2.74-2.96 (m, 2H), 3.47 (dd, J 1.8, 11.2 Hz, 1H), 3.70 (dd, J 3.0, 11.2 Hz, 1H), 7.15-7.17 (m, 2H), 7.23-7.38 (m, 5H), 7.49-7.54 (m, 2H); ¹³C NMR (50 MHz, CDCl₃) δ 18.8, 25.6, 26.1, 28.3, 29.1, 65.3, 78.1, 122.6, 126.5, 126.6, 127.2, 127.47. 127.55, 128.0, 132.2, 133.9, 135.8, 135.9, 143.0; LRMS m/z (rel. int.) 290 (M^+•), 275 (87), 77 (100); HRMS [ESI(+)] calcd. for [C₂₁H₂₂O + Na]⁺ 313.1563, found 313.1559. (±)-(1R,4S)-2,4,5,6-tetrahydro-1,4-dimethyl-4-phenyl-1H-benzo[f] isochromene (trans-3k); R_f = 0.41 (hexanes-EtOAc, 9.5-0.5); IR (film) ν/cm^-1 3069, 2930, 2244, 1489, 766, 700; ¹H NMR (200 MHz, CDCl₃) δ 1.23 (d, J 7.0 Hz, 3H), 1.71 (s, 3H), 1.80-1.94 (m, 1H), 2.05-2.28 (m, 1H), 2.61-2.72 (m, 2H), 2.85-2.96 (m, 1H), 3.51 (dd, J 4.7, 11.5 Hz, 1H), 4.02 (dd, J 4.5, 11.5 Hz, 1H), 7.12-7.19 (m, 2H), 7.28-7.40 (m, 5H), 7.56-7.61 (m, 2H); ¹³C NMR (50 MHz, CDCl₃) δ 17.8, 22.3, 25.3, 28.2, 28.4, 66.3, 79.0, 126.3, 126.4, 127.2, 127.46, 127.53, 128.1, 131.4, 133.8, 136.1, 137.5, 144.5; LRMS m/z (rel. int.) 290 (M^+• , 19), 275 (100); HRMS [ESI(+)] calcd. for [C₂₁H₂₃O + H]⁺291.1743, found 291.1755.

1-Methyl-4,4'-diphenyl-2,4,5,6-tetrahydro-1H-benzo[f ] isochromene (3l): the reaction was performed following the general procedure, but using 1a (0.113 g, 0.600 mmol), 2l (0.109 g, 0.60 mmol), CH₂Cl₂ (5 mL) and I₂ (0.0076, 0.030 mmol). The crude product was purified by flash column chromatography (5% AcOEt in hexanes). Compound 3l (0.0925 g, 0.258 mmol, 43%) was obtained as colorless viscous oil; R_f = 0.71 (hexanes-EtOAc, 1:9); IR (film) ν/ cm^-1 3059, 3023, 2957, 2870, 2246, 1488, 1447, 761, 732, 700; ¹H NMR (200 MHz, CDCl₃) δ 1.34 (d, J 6.6 Hz, 3H), 1.86-1.94 (m, 2H), 2.61-2.70 (m, 2H), 2.86-2.95 (m, 1H), 3.47 (dd, J 4.8, 11.4 Hz, 1H), 3.81 (dd, J 11.6, 4.4 Hz, 1H), 7.10-7.47 (m, 14H); ¹³C NMR (50 MHz, CDCl₃) δ 18.6, 26.8, 28.2, 28.7, 66.1, 85.0, 123.1, 126.3, 126.6, 127.4, 127.5, 127.60, 127.62, 129.2, 129.4, 132.8, 134.0, 135.7, 136.1, 143.3, 144.2; LRMS m/z (rel. int.) 352 (M^+•, 9), 310 (61), 288 (16), 275 (53), 105 (63), 77 (100); HRMS [ESI(+)] calcd. for [C₂₆H₂₄O + H]⁺ 353.1900, found 353.1884.

(1R,1'S)-1-methyl-1,2,3',4',5,6-hexahydro-2'H-spiro[benzo[f ]isochromene-4,1'-napthalene] (3m): the reaction was performed following the general procedure, but using 1a (0.113 g, 0.600 mmol), 2m (0.080 mL, 0.60 mmol), CH₂Cl₂ (5 mL) and I₂ (0.0076, 0.030 mmol).

Compound 3m (0.0998 g, 0.312 mmol, 52%) was obtained as colorless viscous oil; R_f = 0.63 (hexanes-EtOAc, 9:1); IR (film) ν/cm^-1 3061, 3017, 2928, 2868, 2244, 1487, 1450, 762, 730; ¹H NMR (300 MHz, CDCl₃) δ 1.33 (d, J 6.9 Hz, 3H), 1.75-1.90 (m, 2H), 2.01-2.11 (m, 3H), 2.20-2.36 (m, 1H), 2.64-2.72 (m, 2H), 2.76-2.96 (m, 3H), 3.56 (dd, J 2.7, 11.4 Hz, 1H), 4.00 (dd, J 3.3, 11.4 Hz, 1H), 7.06-7.29 (m, 6H), 7.32-7.38 (m, 2H); ¹³C NMR (50 MHz, CDCl₃) δ 18.3, 18.7, 25.5, 28.4, 29.1, 29.7, 34.6, 64.8, 75.8, 122.5, 125.3, 126.4, 126.5, 127.5, 127.6, 128.2, 129.6, 132.9, 134.1, 136.1, 136.4, 137.4, 137.8; LRMS m/z (rel. int.) 316 (M^+• , 75), 301 (3.89), 288 (16), 287 (30), 274 (28), 273 (100); HRMS [ESI(+)] calcd. for [C₂₃H₂₄O + H]⁺ 317.1900, found 317.1902.

(1R,4S)-1-methyl-1,2,5,6-tetrahydrospiro[benzo[f ] isochromene-4,4'-chroman] (3n): the reaction was performed following the general procedure, but using 1a (0.113 g, 0.600 mmol), 2n (0.089 g, 0.60 mmol) CH₂Cl₂ (5 mL) and I₂ (0.0076, 0.030 mmol). Compound 3n (0.071 g, 0.22 mmol, 37%) was obtained as colorless viscous oil; R_f = 0.64 (hexanes-EtOAc, 9:1); IR (film) ν/cm^-1 3064, 3029, 2928, 2948, 1484, 1447, 766, 731; ¹H NMR (300 MHz, CDCl₃) δ 1.35 (d, J 6.6 Hz, 3H), 1.72-2.14 (m, 3H), 2.32-2.48 (m, 1H), 2.32-2.48 (m, 1H), 2.64-2.75 (m, 2H), 2.78-2.84 (m, 1H), 3.60 (dd, J 1.8, 11.2 Hz, 1H), 4.06 (dd, J 3.0, 11.2 Hz, 1H), 4.29-4.38 (m, 1H), 4.50-4.63 (m, 1H), 6.77-6.90 (1H), 7.14-7.30 (m, 5H), 7.38 (d, J 7.4 Hz, 1H); ¹³C NMR (50 MHz, CDCl₃) δ 18.9, 24.8, 28.4, 29.2, 33.2, 62.1, 64.8, 72.1, 117.3, 119.6, 122.5, 123.5, 126.5, 126.8, 127.6, 128.8, 129.5, 133.8, 134.0, 134.2, 136.0, 155.0; LRMS m/z (rel. int.) 316 (M^+• , 75), 290 (35), 289 (80), 273 (68), 247 (39), 231 (53, 32 (100); HRMS [ESI(+)] calcd. for [C₂₂H₂₂O₂+Na]⁺ 341.1512, found 341.1516.

(+)-(4S,4aS,7R,8aS)-2,2,4,7-tetramethyloctahydro-2H-chromen-4-ol (5): the reaction was performed following the general procedure, but using 1b (0.154 g, 1.00 mmol), acetone (0.089 mL, 1.2 mmol), CH₂Cl₂ (5 mL) and I₂ (0.013, 0.050 mmol). Compound 5 (0.103 g, 0.486 mmol, 49%) was obtained as a white solid; mp 105-106 ºC; [α]_D²⁰ 5.8 (c 1.00, CHCl₃); R_f = 0.12 (hexanes:EtOAc, 9:1); IR (film) ν/cm^-1 3465, 3004, 2933, 2883, 1375, 1159; ¹H NMR (200 MHz, CDCl₃) δ 0.93 (d, J 6.6 Hz, 3H), 1.01-1.13 (m, 5H), 1.18 (s, 6H), 1.39 (s, 3H), 1.47 (br, 1H), 1.54 (br, 1H), 1.60 (br, 1H), 1.67-1.94 (m, 3H), 3.51-3.64 (m, 1H); ¹³C NMR (50 MHz, CDCl₃) δ 22.3, 22.4, 24.4, 29.6, 31.3, 32.8, 34.4, 41.8, 49.1, 49.4, 68.6, 69.9, 71.2; LRMS m/z (rel. int.) 198 (2.8), 197 (25.5), 194 (7.2), 179 (7.2), 139 (21.1), 121 (16.1), 95 (18.7), 93 (17.1), 81 (61.0), 71 (35), 67 (47.7), 59 (69.2), 55 (100); HRMS [ESI(+)] calcd. for [C₁₃H₂₄O₂+ H]⁺ 213.1849, found 213.1854.

Supplementary Information

NMR copies are available free of charge at http://jbcs.sbq.org.br as a PDF file.

Acknowledgments

The authors wish to thank FAPESP, CNPq and CAPES for financial support. The authors also wish to thank Dr. S. A. P. Quintiliano for initial experiments.

Submitted: May 5, 2013

Published online: August 6, 2013

FAPESP has sponsored the publication of this article.

Supplementary Information

The supplementary material is available in pdf: [Supplementary material]

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Publication Dates

• Publication in this collection
  24 Sept 2013
• Date of issue
  Sept 2013

History

• Received
  05 May 2013
• Accepted
  06 Aug 2013