Chinese Chemical Letters  2016, Vol. 27 Issue (9): 1537-1540   PDF    
Citation
Jian Zhang, Jin-Long Wu.Tandem intramolecular Diels-Alder/retro-Diels-Alder cycloaddition of 2H-chromen-2-one as dienes with the expulsion of CO2[J]. Chin. Chem. Lett., 2016,27(9): 1537-1540  
Tandem intramolecular Diels-Alder/retro-Diels-Alder cycloaddition of 2H-chromen-2-one as dienes with the expulsion of CO2
Jian Zhang, Jin-Long Wu     
Laboratary of Asymmetry Catalysis and synthesis, Department of Chemistry, Zhejiang University, Hangzhou 310027, China
Received Feb 15, 2016, Received in revised form Mar 2, 2016, Accepted Mar 30, 2016, Available online Sep 22, 2016
* Corresponding author. E-mail address: wyz@zju.edu.cn (J.-L. Wu)
Abstract: To study the intramolecular Diels-Alder cycloadditon of 2H-chromen-2-one as a diene, a series of chiral N-allyl-N-benzylamides that contain a 2H-chromen-2-one moiety were designed for the synthesis of benzo[f]isoindol-1-ones via an intramolecular Diels-Alder and a subsequent retro-Diels-Alder cycloaddition with the expulsion of CO2. Both the yield (80%-89%) and absolute stereocontrol of the tandem reaction were high when an electron-withdrawing group was attached to the dienophile. The double bond in the styrene substructure remained in the products could be further derivatized by dihydroxylation.
Key words: 2H-Chromen-2-one     Intramolecular Diels-Alder     Retro-Diels-Alder     Benzo[f]isoindol-1-one     Dihydroxylation    
1. Introduction

Because of the stability of an aromatic ring, the exocyclic double bond in styrene commonly reacts as a dienophile in [4 + 2] cycloaddition reactions[1] and it is quite difficult for styrene to participate as a diene in thermal Diels-Alder cycloaddition unless extremely reactive dienophiles are employed[2]. 2H-pyran-2-one and its derivatives are a class of important electron-rich diene in the Diels-Alder reaction[3] and are widely used in organic synthesis[4]. There is a feature of this type of dienes in the Diels-Alder reaction: Retro-Diels-Alder reaction will happen under certain conditions by eliminating one molecule of CO2, which introduces a carbon-carbon double bond in the ring[5]. Several reports claimed that 2H-chromen-2-one, a kind of 2H-pyran-2-one fused with a benzene ring, can be used in the Diels-Alder cycloaddition as a dienophile[6]. However, only one case where it was used as a diene was reported in the tandem intramolecular Diels-Alder (IMDA) and retro-Diels-Alder cycloaddition with acetylene as shown in Scheme 1[7]. The reaction must be carried out in a sealed tube placed in a 300 ℃ bath, and surprisingly, the acetylenic hydrogen replaced by an electron-withdrawing group (EWG), carboethoxy, 1e failed to cyclize to form 2e. In our continuous works on synthesis of polycyclic compounds using IMDA reaction[8], herein, we report the tandem IMDA and retro-Diels-Alder reaction of chiral N-(4-methoxybenzyl)-2-oxo-N-(1-phenylbut-3-en-2-yl)-2H-chromene-3-carboxamides for stereocontrolled synthesis of 3-benzyl-2-(4-methoxybenzyl)-2, 3, 3a, 4-tetrahydro-1H-benzo[f]isoindol-1-ones under relatively mild conditions.

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Scheme. 1. Tandem IMDA and retro-Diels–Alder reaction of 2H-chromen-2-one with acetylene.

2. Experimental 2.1. General procedure for the synthesis of 4a-g

A solution of 3 (0.1 mmol) in CH3CN (2 mL) in a sealed vial was heated in an oil bath at 160 ℃. After the reaction completed (monitored by TLC analysis), the solvent was removed under reduced pressure. The residue was purified by chromatography on silica gel (ethyl acetate/petroleum ether=1/3) to give 4 (Scheme 2).

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Scheme. 2. Synthesis of compounds 4a–g.

Ethyl (3S, 3aS, 4R)-3-benzyl-2-(4-methoxybenzyl)-4-methyl-1-oxo-2, 3, 3a, 4-tetrahydro-1H-benzo[f]isoindole-4-carboxylate  4a: White crystalline solid, yield 82%, mp 204-205 ℃ (EtOAc-hexane); [α]D25 +13.9 (c 1.0, CHCl3); Rf=0.20 (20% EtOAc in hexane); IR (film, cm-1): 3061, 3028, 2979, 2933, 2836, 1721, 1685, 1611, 1512, 1447, 1409, 1298, 1247, 1174, 1093, 1031, 909, 755, 731, 700; 1H NMR (400 MHz, CDCl3): δ 7.29-7.21 (m, 6H), 7.19 (d, 1H, J=3.2 Hz), 7.11-7.09 (m, 2H), 6.94-6.90 (m, 3H), 6.78 (d, 2H, J=8.8 Hz), 5.34 and 3.91 (ABq, 2H, J=14.8 Hz), 4.32 (dq, 1H, J =10.8, 7.2 Hz), 4.19 (dq, 1H, J=10.8, 7.2 Hz), 3.79 (s, 3H), 3.76 (dt, 1H, J=5.2, 3.6 Hz), 3.65 (dd, 1H, J=4.8, 3.2 Hz), 3.12 (dd, 1H, J=15.2, 3.2 Hz), 2.66 (dd, 1H, J=15.2, 5.6 Hz), 1.31 (t, 3H, J=7.2 Hz), 1.11 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 175.8, 167.0, 159.0, 139.6, 136.4, 132.2, 131.6, 129.7, 129.6 (×2), 129.2 (×2), 129.1, 128.6 (×2), 127.9, 127.7, 126.8, 126.0, 125.4, 114.0 (×2), 61.6, 55.6, 55.2, 51.2, 44.2, 42.9, 38.2, 17.2, 14.2; HRMS (+EI) calculated for C31H31NO4+ (M+) 481.2253; found 481.2246.

(3S, 3aR)-3-Benzyl-2-(4-methoxybenzyl)-4, 4-dimethyl-2, 3, 3a, 4-tetrahydro-1H-benzo[f]isoindol-1-one 4e: Colorless oil, yield 11%, [α]D25 +7.6 (c 1.0, CHCl3); Rf=0.19 (25% EtOAc in hexane); IR (film, cm-1): 3066, 3030, 3003, 2965, 2929, 2866, 2834, 1676, 1611, 1516, 1453, 1409, 1304, 1239, 1174, 1031, 834, 811, 751, 703; 1H NMR (400 MHz, CDCl3): δ 7.27-7.19 (m, 8H), 7.09-7.04 (m, 4H), 6.85 (d, 2H, J=8.8 Hz), 5.40and 4.01(ABq, 2H, J=14.8 Hz), 3.81(s, 3H), 3.67-3.63 (m, 1H), 3.02-2.92 (m, 2H), 2.78-2.75 (m, 1H), 1.03 (s, 3H), 0.74 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 167.4, 159.1, 144.8, 136.6, 133.7, 132.5, 129.8 (×2), 129.5, 129.4 (×2), 128.9, 128.7 (×2), 128.1, 126.9, 126.8, 126.7, 123.6, 114.0 (×2), 56.2, 55.3, 46.0, 44.1, 40.1, 37.5, 24.3, 21.6; HRMS (+EI) calculated for C29H29NO2+ (M+) 423.2198; found 423.2204.

2.2. General procedure for the synthesis of 5a-c

To a solution of 4 (0.1 mmol) in a mixed solvent of 2-methyl-2-propanol (1 mL) and water (1 mL) were added methanesulfonamide (0.1 mmol) and AD-mix α (145 mg). After stirring at 0 ℃ for 10-24 h, the reaction mixture was quenched with saturated aqueous Na2S2O3 (5 mL) and stirred at room temperature for another 20 min, then the mixture was extracted with ethyl acetate (10 mL × 3). The combined organic phase was dried over anhydrous Na2SO4, filtrated and concentrated under reduced pressure. The residue was purified by chromatography on silica gel (EtOAc/ PE=1/1) to give 5 (Scheme 3).

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Scheme. 3. Synthesis of compounds 5a–c.

(1S, 3aS, 4R, 9R, 9aS)-1-Benzyl-3a-hydroxy-2-(4-methoxybenzyl)-9-methyl-3a, 4, 9, 9a-tetrahydro-1H-4, 9-(epoxymethano)benzo[f]-isoindole-3, 10(2H)-dione 5a: White crystalline solid, yield 90%; mp 102-107 ℃ (EtOAc-hexane); [α]D25 -4.2 (c 1.0, CHCl3); Rf=0.22 (50%EtOAcinhexane); IR(film, cm-1):3387, 3063, 3033, 2980, 2938, 2840, 1757, 1676, 1513, 1453, 1373, 1245, 1043, 1004, 843, 778, 745, 701; 1H NMR (400 MHz, CDCl3): δ 7.48-7.46 (m, 1H), 7.41-7.34 (m, 2H), 7.33-7.25 (m, 3H), 6.99-6.94 (m, 3H), 6.67 (d, 2H, J=8.8 Hz), 6.23 (d, 2H, J=8.8 Hz), 5.64 (s, 1H), 4.78 and 3.72 (ABq, 2H, J=14.8 Hz), 3.83 (s, 3H), 3.15 (dd, 1H, J=13.2, 3.6 Hz), 2.73 (ddd, 1H, J=9.6, 3.6, 2.4 Hz), 2.55 (dd, 1H, J=13.2, 9.6 Hz), 2.34 (d, 1H, J=2.4 Hz), 0.76 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 173.3, 170.7, 159.0, 135.5, 135.3, 134.3, 129.8, 129.7 (×2), 129.4 (×2), 129.0 (×2), 128.1, 127.4, 125.4, 125.3, 123.9, 114.1 (×2), 82.1, 81.5, 58.1, 55.3, 47.8, 47.6, 43.8, 39.8, 12.6; HRMS (+EI) calculated for C29H27NO5+ (M+) 469.1889; found 469.1881.

2.3. Synthesis of 6c[9]

Some biological studies on the approved and developing γ-lactam drugs showed that the N-H type lactams are more active than the corresponding N-substituted one[11], therefore we completed the transformation of 4c to 6c as an example using ceric (Ⅳ) ammonium nitrate (CAN). To a solution of 4c (72 mg, 0.137 mmol) in a mixed solvent of CH3CN (3 mL) and H2O (1 mL) was added ceric ammonium nitrate (298 mg, 0.544 mmol) in one portion. After stirring for 30 min at room temperature, H2O (3 mL) was added and then the mixture was extracted with ethyl acetate (10 mL × 3). The combined organic layer was washed with saturated aqueous NaHCO3 (1.5 mL × 3) and brine (1.5 mL). The organic phase was dried over anhydrous Na2SO4, filtrated and concentrated under reduced pressure. The residue was purified by chromatography on silica gel (ethyl acetate/petroleum=1/1) to give 6c (46 mg, 83%) as a colorless oil (Scheme 4).

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Scheme. 4. Transformation from 4c to 6c by removing PMB with CAN.

Ethyl (3S)-3-benzyl-4-methyl-7-nitro-1-oxo-2, 3, 3a, 4-tetrahydro-1H-benzo[f]isoindole-4-carboxylate 6c: Yield 83%; [α]D15 +2.1 (c 1.0, CHCl3); Rf=0.29 (50% EtOAc in hexane); IR (film, cm-1): 3405, 3214, 3066, 3024, 2979, 2935, 2873, 1730, 1697, 1608, 1584, 1519, 1456, 1346, 1292, 1239, 1090, 1050, 1016, 909, 825, 736, 698; 1H NMR (400 MHz, CDCl3): δ 8.14-8.12 (m, 2H), 7.35 (t, 2H, J=7.2 Hz), 7.29 (d, 1H, J=7.2 Hz), 7.25 (d, 1H, J=3.2 Hz), 7.21 (d, 1H, J=7.2 Hz), 7.19 (d, 2H, J=8.0 Hz), 6.18 (br s, 1H), 4.47-4.34 (m, 2H), 3.98-3.93 (m, 1H), 3.70 (dd, 1H, J=6.0, 3.6 Hz), 2.98 (dd, 1H, J=13.6, 2.8 Hz), 2.60 (dd, 1H, J=13.6, 10.0 Hz), 1.39 (t, 3H, J=7.2 Hz), 1.38 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 174.7, 167.1, 147.3, 146.1, 136.4, 135.3, 132.8, 129.1 (×2), 129.0 (×2), 127.3, 126.7, 124.32, 124.29, 123.4, 62.3, 54.6, 51.0, 46.4, 42.0, 17.8, 14.2; HRMS (+EI) calcd. for C23H22N2O5+ (M+) 406.1529; found 406.1538.

3. Results and discussion

We designed and synthesized a series of chiral N-allyl-N-benzylamides containing the moiety of 2H-chromen-2-one (3a-g) for the IMDA reaction with the expectation that the 2H-chromen-2-one moiety and the allyl group act as the diene and the dienophile, respectively. The optimized reaction conditions are by heating a solution of chiral amide 3 inacetonitrile in a sealed vial placedin an oil bath at 160 ℃. The chiral N-(4-methoxybenzyl)-2-oxo-N-(1-phenylbut-3-en-2-yl)-2H-chromene-3-carboxamides 3a-g were transformed into tricyclic compounds, 3-benzyl-2-(4-methoxy-benzyl)-2, 3, 3a, 4-tetrahydro-1H-benzo[f]isoindol-1-ones 4a-g (entries 1-7, Table 1) via an IMDA followed by a retro-Diels-Alder reaction with the expulsion of CO2. The stereochemistry of these adducts was absolutely controlled by the preexisting chiral center.

Table 1
Results of tandem IMDA and retro-Diels–Alder reaction of 3.

The reactivity of amides varied depending on the substitution pattern at the terminal of the allyl double bond. As shown in Table 1, those amides attached to a trans electron-withdrawing group, carboethoxy, at the terminal of the allyl double bond 3a-d reacted to furnish 4a-d within 12 h in high yields (80%-89%) (Table 1, entries 1-4). However, amides attached to two methyl groups at the terminal allyl double bond 3e-g were transformed into 4e-g in low yields (11%-28%) and much longer time (5 days) was needed (Table 1, entries 5-7). These results show that an electron-withdrawing group on the dienophiles facilitates the reaction but an electron-donating group is unfavorable. Interestingly, these results are completely different from that of the IMDA reaction of 2H-chromen-2-one with acetylenic groups. That reaction required higher temperature (300 ℃) and was retarded by an electron-withdrawing group, carboethoxy, attached to the terminal acetylene (Scheme 1). The substituents on the benzene ring of 2H-chromen-2-one do not apparently affect the reactivity (entries 1-3 and 5-7, Table 1), but weak electron-withdrawing groups on the benzene ring of 2H-chromen-2-one facilitate the reaction (entries 2 and 6, Table 1).

The structure of the product 4a, depicted in Fig. 1, was determined by X-ray diffraction analysis. The crystallographic data of 4a have been deposited in the Cambridge Crystallographic Data Centre (No. CCDC 1451810). The structures of 4b-g were deduced from 4a by comparing the 1H NMR data. The coupling constants between H3 and H3a of 4b-g are in a range of 3.6-5.6 Hz and similar to that of 4a (4.8 Hz). Paddon-Row and Sherburn[10] performed computational studies on the stereoselectivity in IMDA reactions of penta-1, 3-dienyl acrylates and found that trans adducts were generally favored. Accordingly, we hypothesized a possible pathway of cycloaddition of 3a as shown in Scheme 5. The chiral N-allyl-N-benzylamide transforms into IMDA adduct B via transition state A, and the subsequent elimination of carbon dioxide from B generates the 2, 3, 3a, 4-tetrahydro-1H-benzo[f]isoindol-1-one derivative 4a.

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Figure 1. X-ray structure for 4a.

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Scheme. 5. An assumed possible pathway from 3a to 4a.

Due to the C9-C9a double bond, these 2, 3, 3a, 4-tetrahydro-1H-benzo[f]isoindol-1-ones can be subjected to further modifications. Stereo-controlled dihydroxylation of 4a-c by AD-mix α followed by esterification afforded 5a-c in high yields (83%-90%) (Scheme 3). It is surprising to us that the formed products had a δ-lactone structure. These results show that the two introduced hydroxyl groups were kept in the same face of the carbon ring with carboethoxy, which led to the formation of the δ-lactone with the hydroxyl at the C9 position under basic conditions.

4. Conclusion

The tandem IMDA/retro-Diels-Alder reaction of chiral N-allyl-N-benzylamides containing 2H-chromen-2-one constitutes an absolute stereo-controlled entry to 2, 3, 3a, 4-tetrahydro-1H-ben-zo[f]isoindol-1-ones. The reactivity was affected by groups attached in the dienophile, and an electron-withdrawing group facilitates the reaction. Adducts can be further modified by removing the PMB group or dihydroxylation of the double bond. Further studies on the scope and application of this tandem IMDA/ retro-Diels-Alder reaction of N-allyl-N-benzylamides containing 2H-chromen-2-ones are in progress.

Acknowledgment

This work was supported by the research grant from the National Natural Science Foundation of China (No. 21172191). Mr. Jiyong Liu of the X-ray crystallography facility of Zhejiang University is acknowledged for his assistance in the crystal structure analysis.

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