2018, Vol. 32
Michael加成反应是一种高效的构建C—C键的重要方法[1-3].近年来, 有机小分子催化的不对称Michael反应引起了广泛关注[4-7].脲/硫脲衍生物由于具有很强的氢键活化能力, 成功的实现了对多种反应的高对映选择性催化, 尤其在各类底物的不对称Michael加成反应中取得了很大进展[8-25].然而, 蒽酮化合物作为亲核试剂在不对称Michael加成反应的文献报道较少[26-30]. 2007年, Shi首次报道了金鸡纳碱有机催化的蒽酮与β-硝基烯烃的不对称Michael加成反应, 得到了80%~99%ee的对映选择性[27]. 2009年, Yuan报道了叔胺硫脲类有机催化剂在该反应中的应用, 得到了60%~94%ee的立体选择性[28]. 2010年He报道了伯胺硫脲有机催化蒽酮不对称Michael加成反应, 得到了65%~86%的对映选择性[29].这里我们报道系列脲/硫脲催化剂1a-g (Fig. 1)有机催化蒽酮与β-硝基苯烯烃的不对称Michael加成反应, 以期扩大该反应的催化剂类型.
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图 1 催化剂1a-g的结构 Figure 1 The structures of catalysts 1a-g |
Bruker Avance-500型核磁共振谱仪(均以CDCl3为溶剂, TMS为基准物质, 德国Bruker公司); MICROMASS Quattro Premier型质谱仪(美国waters公司); LC-20A高效液相色谱仪(日本岛津公司), Daicel Chiralpak AD-H, Chiralcel OD-H手性色谱柱(日本大赛璐公司).脲及硫脲衍生物为上海大赛璐药物手性技术(上海)有限公司产品, 其他试剂均为市售分析纯产品.
1.2 不对称Michael加成反应于5 mL圆底烧瓶中依次加入反式硝基苯乙烯(29.8 mg, 0.2 mmol), 催化剂(0.01 mmol), 蒽酮(46.6 mg, 0.24 mmol), 二氯甲烷3.0 mL, 室温搅拌反应12~18 h, TLC监测.反应完毕后, 经硅胶柱层析分离, Hex:EtOAc(9:1)洗脱, 得到产品3a-m.
10-(2-硝基-1-苯基乙基)-10H-蒽-9-酮3a:白色固体; mp=145~147 ℃, [文献值[28] mp=146.8~149.0 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.07 (d, J = 8.0 Hz, 1H), 7.98 (d, J = 8.0 Hz, 1H), 7.67-7.59 (m, 2H), 7.53-7.46 (m, 2H), 7.45-7.40 (m, 2H), 7.17-7.13 (m, 1H), 6.95 (t, J = 7.5 Hz, 2H), 6.05 (d, J = 8.0 Hz, 2H), 4.89 (dd, J =9.0, 13.0 Hz, 1H), 4.60 (dd, J = 7.0, 13.0 Hz, 1H), 4.55 (d, J = 3.5 Hz, 1H), 4.08-4.04 (m, 1H); HPLC (Daicel Chiralpak AD-H, Vhex:ViPrOH= 97:3, 0.6 mL/min, 254 nm), tR: 45.9 min (major), 51.6 min (minor). [α]D25 = + 23.9 (c = 0.50 in CHCl3), 文献值[28] [α]D20 = +25.4 (c = 0.48 in CHCl3).
10-[1-(2-氟苯基)-2-硝基乙基]-10H-蒽-9-酮3b:白色固体; mp = 117~119 ℃; 1H NMR (500 MHz, CDCl3) δ 8.13 (d, J = 7.5 Hz, 1H), 8.07 (d, J = 7.5 Hz, 1H), 7.66-7.61 (m, 1H), 7.57-7.49 (m, 3H), 7.48-7.44 (m, 1H), 7.26-7.18 (m, 2H), 6.88-6.78 (m, 2H), 6.07 (t, J = 7.5 Hz, 1H), 4.74 (dd, J =8.0, 13.5 Hz, 1H), 4.60 (d, J = 9.0, 1H), 4.54 (dd, J = 8.0, 13.5 Hz, 1H), 4.39-4.35 (m, 1H); HPLC (Daicel Chiralpak AD-H, Vhex:ViPrOH= 97:3, 0.6 mL/min, 254 nm), tR: 54.4 min (major), 64.1 min (minor). [α]D25 = + 17.5 (c = 0.55 in CHCl3).
10-[1-(2-氯苯基)-2-硝基乙基]-10H-蒽-9-酮3c:白色固体; mp = 123~124 ℃, [文献值[27] mp = 126.2~126.7 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.18 (d, J = 7.5 Hz, 1H), 8.15 (d, J = 7.5 Hz, 1H), 7.70-7.64 (m, 2H), 7.54-7.51 (m, 1H), 7.47-7.43 (m, 1H), 7.42-7.35 (m, 2H), 7.23-7.19 (m, 1H), 7.02 (t, J = 7.5 Hz, 1H), 6.80 (d, J = 7.0 Hz, 1H), 6.23 (d, J = 8.0 Hz, 1H), 4.72 (bs, 1H), 4.66 (d, J = 3.5 Hz, 1H), 4.44-4.38 (m, 2H); HPLC (Daicel Chiralpak AD-H, Vhex:ViPrOH= 97:3, 0.6 mL/min, 254 nm), tR: 33.4 min (major), 53.9 min (minor). [α]D25 = +18.6 (c = 0.60 in CHCl3), 文献值[28] [α]D20 = +14.8 (c = 0.54 in CHCl3).
10-[1-(2-溴苯基)-2-硝基乙基]-10H-蒽-9-酮3d:白色固体; mp = 100~102 ℃, [文献值[28] mp = 62.8~65.6 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.22-8.18 (m, 2H), 7.80 (bs, 1H), 7.71-7.68 (m, 1H), 7.61 (d, J = 6.5 Hz, 1H), 7.55 (t, J = 7.5 Hz, 1H), 7.49-7.45 (m, 1H), 7.38 (t, J = 7.5 Hz, 1H), 7.17-7.13 (m, 1H), 7.07 (t, J = 7.5 Hz, 1H), 6.72-6.71 (m, 1H), 6.25 (dd, J = 1.5, 8.0 Hz, 1H), 4.73 (bs, 1H), 4.72 (s, 1H), 4.36 (d, J = 6.0 Hz, 2H); HPLC (Daicel Chiralpak AD-H, Vhex:ViPrOH= 97:3, 0.6 mL/min, 254 nm), tR: 42.3 min (major), 61.9 min (minor). [α]D25=+ 8.0 (c = 0.53 in CHCl3), 文献值[28] [α]D20 = +7.1 (c = 0.74 in CHCl3).
10-[1-(3-氟苯基)-2-硝基乙基]-10H-蒽-9-酮3e:白色固体; mp = 128~130 ℃, [文献值[28] mp = 123.8~126.9 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.09 (d, J = 7.5 Hz, 1H), 8.02 (d, J = 7.5 Hz, 1H), 7.69-7.59 (m, 2H), 7.55-7.40 (m, 4H), 6.98-6.82 (m, 2H), 5.88 (d, J = 7.5 Hz, 1H), 5.80-5.76 (m, 1H), 4.86 (dd, J = 8.5, 13.5 Hz, 1H), 4.59 (dd, J = 8.5, 13.5 Hz, 1H), 4.55 (d, J = 3.5 Hz, 1H), 4.08-4.02 (m, 1H); HPLC (Daicel Chiralpak AD-H, Vhex:ViPrOH= 97:3, 0.6 mL/min, 254 nm), tR: 65.9 min (major), 71.9 min (minor). [α]D25 = + 28.5 (c = 0.52 in CHCl3), 文献值[28] [α]D20 = +26.3 (c = 0.58 in CHCl3).
10-[1-(3-溴苯基)-2-硝基乙基]-10H-蒽-9-酮3f:白色固体; mp = 120~121 ℃, [文献值[28] mp = 114.7~117.1 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.11 (d, J = 7.5 Hz, 1H), 8.02 (d, J = 7.5 Hz, 1H), 7.69-7.60 (m, 2H), 7.56-7.41 (m, 4H), 7.27 (d, J = 9.0 Hz, 1H), 6.83 (t, J =8.0 Hz, 1H), 6.14 (s, 1H), 6.01(d, J = 7.5 Hz, 1H), 5.96 (d, J =7.5 Hz, 1H), 4.85 (dd, J =8.5, 13.5 Hz, 1H), 4.59-4.54 (m, 2H), 4.04-3.98 (m, 1H); HPLC (Daicel Chiralpak AD-H, Vhex:ViPrOH= 97:3, 0.6 mL/min, 254 nm), tR: 59.6 min (major), 73.7 min (minor). [α]D25 = + 35.2 (c = 0.42 in CHCl3), 文献值[28] [α]D20 = +31.0 (c = 0.58 in CHCl3).
10-[1-(3-甲基苯基)-2-硝基乙基]-10H-蒽-9-酮3g:白色固体; mp = 107~109 ℃, [文献值[28] mp = 111.5~113.9 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.06 (d, J = 8.0 Hz, 1H), 7.97 (d, J = 8.0 Hz, 1H), 7.66-7.58 (m, 2H), 7.52-7.47 (m, 2H), 7.43-7.38 (m, 2H), 6.95 (d, J =7.5 Hz, 1H), 6.82 (t, J =7.5 Hz, 1H), 5.86 (d, J =7.5 Hz, 1H), 5.77 (s, 1H), 4.85 (dd, J =9.0, 13.0 Hz, 1H), 4.57 (dd, J =7.0, 13.5 Hz, 1H), 4.52 (d, J =3.5 Hz, 1H), 4.01-3.98 (m, 1H), 2.02 (s, 3H); HPLC (Daicel Chiralpak AD-H, Vhex:ViPrOH= 97:3, 0.6 mL/min, 254 nm), tR: 36.1 min (major), 53.0 min (minor). [α]D25 = + 37.1 (c = 0.45 in CHCl3), 文献值[28] [α]D20 = +33.2 (c = 0.60 in CHCl3).
10-[1-(4-氟苯基)-2-硝基乙基]-10H-蒽-9-酮3h:白色固体; mp = 165~167 ℃, [文献值[28] mp = 170.1~172.0 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.08 (d, J = 7.5 Hz, 1H), 8.00 (d, J = 7.5 Hz, 1H), 7.67-7.60 (m, 2H), 7.53-7.42 (m, 4H), 6.64 (d, J = 7.5 Hz, 2H), 6.02-5.99 (m, 2H), 4.87 (dd, J =9.0, 13.0 Hz, 1H), 4.59-4.52 (m, 2H), 4.06-4.02 (m, 1H); HPLC (Daicel Chiralpak AD-H, Vhex:ViPrOH= 97:3, 0.6 mL/min, 254 nm), tR: 53.3 min (major), 58.6 min (minor). [α]D25 = +33.5 (c = 0.65 in CHCl3), 文献值[28] [α]D20 = +31.0 (c = 0.46 in CHCl3).
10-[1-(4-氯苯基)-2-硝基乙基]-10H-蒽-9-酮3i:白色固体; mp = 170~172 ℃, [文献值[28] mp = 168.7~171.2 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.11 (d, J = 8.0 Hz, 1H), 8.03 (d, J = 8.0 Hz, 1H), 7.68-7.59 (m, 2H), 7.54-7.44 (m, 3H), 7.40 (d, J = 7.5 Hz, 1H), 6.95 (d, J = 8.5 Hz, 2H), 6.02 (d, J = 8.0 Hz, 2H), 4.85 (dd, J = 8.5, 13.0 Hz, 1H), 4.57-4.52 (m, 2H), 4.06-4.02 (m, 1H); HPLC (Daicel Chiralpak AD-H, Vhex:ViPrOH= 97:3, 0.6 mL/min, 254 nm), tR: 41.9 min (major), 47.5 min (minor). [α]D25 = + 24.3 (c = 0.50 in CHCl3), 文献值[28] [α]D20 = +21.7 (c = 0.40 in CHCl3).
10-[1-(4-甲基苯基)-2-硝基乙基]-10H-蒽-9-酮3j:白色固体; mp = 158~160 ℃, [文献值[28] mp = 156.0~158.1 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.08 (d, J = 7.5 Hz, 1H), 8.00 (d, J = 7.5 Hz, 1H), 7.67-7.58 (m, 2H), 7.53-7.49 (m, 2H), 7.45-7.38 (m, 2H), 6.76 (d, J =8.0 Hz, 2H), 5.96 (d, J =8.0 Hz, 2H), 4.84 (dd, J =9.0, 13.0 Hz, 1H), 4.57-4.52 (m, 2H), 4.05-4.00 (m, 1H), 2.22 (s, 3H); HPLC (Daicel Chiralpak AD-H, Vhex:ViPrOH= 97:3, 0.6 mL/min, 254 nm), tR: 34.0 min (major), 36.3 min (minor). [α]D25 = + 28.9 (c = 0.56 in CHCl3), 文献值[28] [α]D20 = +25.4 (c = 0.62 in CHCl3).
10-[1-(4-硝基苯基)-2-硝基乙基]-10H-蒽-9-酮3k:白色固体; mp = 189~191 ℃, [文献值[28] mp = 194.5~196.1 ℃]; 1H NMR (500 MHz, CDCl3) δ 9.90 (d, J = 7.5 Hz, 1H), 7.85-7.69 (m, 6H), 7. 58-7. 48 (m, 3H), 6.46 (d, J = 8.5 Hz, 2H), 5.47 (dd, J = 5.0, 13.5 Hz, 1H), 5.06 (dd, J = 10.0, 13.5 Hz, 1H), 4.95 (d, J = 4.0 Hz, 1H), 4.15-4.10 (m, 1H); HPLC (Chiralpak AD-H, Vhex:ViPrOH=70:30, 1.0 mL/min, 254 nm), tR: 12.7 min (major), 16.9 min (minor). [α]D25 = + 25.1 (c = 0.55 in CHCl3), 文献值[28] [α]D20 = +21.2 (c = 0.42 in CHCl3).
10-[1-(4-甲氧基苯基)-2-硝基乙基]-10H-蒽-9-酮3l:白色固体; mp = 117~119 ℃, [文献值[28] mp = 119.8~122.7 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.07 (d, J = 8.0 Hz, 1H), 7.99 (d, J = 7.5 Hz, 1H), 7.66-7.65 (m, 2H), 7. 50-7. 38 (m, 4H), 6.47 (d, J = 8.5 Hz, 2H), 5.95 (d, J = 8.5 Hz, 2H), 4.83 (dd, J = 9.0, 13.0 Hz, 1H), 4.55 (dd, J = 8.0, 13.0 Hz, 1H), 4.49 (d, J = 3.5 Hz, 1H), 4.03-3.97 (m, 1H), 3.68 (s, 3H); HPLC (Chiralcel OD-H, Vhex:ViPrOH=70:30, 1.0 mL/min, 254 nm), tR: 21.5 min (major), 29.2 min (minor). [α]D25 = +20.8 (c = 0.38 in CHCl3), 文献值[28] [α]D20 = +18.7 (c = 0.74 in CHCl3).
10-[1-环己基-2-硝基乙基]-10H-蒽-9-酮3m:白色固体; mp = 123~125 ℃, [文献值[28] mp = 127.3~130.8 ℃]; 1H NMR (500 MHz, CDCl3) δ 8.30 (t, J = 8.5 Hz, 2H), 7.67-7.60 (m, 2H), 7.57-7.42 (m, 4H), 4.45 (dd, J = 9.0, 13.0 Hz, 1H), 4.35 (d, J = 2.5 Hz, 1H), 4.27 (dd, J = 5.0, 13.0 Hz, 1H), 2.73-2.65 (m, 1H), 1.62-1.48 (m, 2H), 1.44-1.35 (m, 2H), 1.20-1.02 (m, 3H), 0.97-0.75 (m, 2H), 0.45-0.25 (m, 2H); HPLC (Chiralpak AD-H, Vhex:ViPrOH=80:20, 1.0 mL/min, 254 nm), tR: 8.9 min (major), 9.4 min (minor). [α]D25 = +63.6 (c = 0.40 in CHCl3), 文献值[28] [α]D20 = +61.0 (c = 0.24 in CHCl3).
2 结果与讨论 2.1 催化剂1a-g催化不对称Michael加成反应将催化剂1a-g用于反式硝基苯乙烯与蒽酮的不对称Michael加成反应, 以二氯甲烷为溶剂, 室温反应, 考察催化剂的催化性能, 结果见表 1.
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表 1 反式硝基苯乙烯和蒽酮的不对称Michael加成反应结果a Table 1 Asymmetric Michael addition of nitrostyrene and anthronea |
由表 1反应结果可以得出以下结论: 7种(硫)脲类催化剂在二氯甲烷中均能顺利催化硝基苯乙烯与蒽酮的不对称Michael加成反应, 得到80%~92%的产率.其中硫脲催化剂1f催化该反应得到了最好的对映选择性(85% ee, entry 6), 产品的构型, 通过测定旋光值, 对比文献报道[27]的旋光值确定主要产物的构型为S型.
2.2 反应条件的优化将上述最好的催化剂1f用于硝基苯乙烯与蒽酮的不对称Michael加成反应中, 考察溶剂、温度、催化剂用量等因素对反应立体选择性的影响, 以期获得更好的催化剂体系.结果见表 2.
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表 2 反式硝基苯乙烯与蒽酮的不对称Michael加成反应条件筛选a Table 2 Screening of Reaction Conditions for the Asymmetric Michael Addition Reactiona |
由表 2结果可以看出: (1)溶剂对反应的立体选择性有显著影响, 其中二氯甲烷和氯仿作为溶剂均得到了最好的ee值(entries 1, 8).考虑到氯仿溶剂的毒性大, 选择二氯甲烷为溶剂; (2)降温对反应的立体选择性没有改善, 反应温度由室温降至0 ℃, 反应的立体选择性明显降低(entry 11vs entry 1); (3)催化剂的用量由10%(摩尔百分数)增加至20%或降至5%, 反应的对映体过量值均增加了6%(entries 9, 10 vs entry 1), 反应产率以20%(摩尔百分数)用量时略高.但是, 考虑到催化剂用量越少, 反应的成本越低, 因此, 选择5%(摩尔百分数)的催化剂用量, 以及延长反应时间来提高反应产率; (4)当反应溶剂量加倍, 既反应体系稀释条件下, 反应的产率和立体选择性都有所下降.综上所述, 筛选出的最佳催化剂体系为: 5%(摩尔百分数)的催化剂1f, 二氯甲烷为溶剂, 室温反应.
2.3 底物的扩展将筛选出的催化条件应用于不同取代β硝基芳基乙烯的不对称Michael加成反应, 考察催化剂体系的普适性, 结果见表 3.
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表 3 蒽酮和不同硝基烯烃的不对称Michael加成反应a Table 3 Asymmetric Michael Addition Reactions of Anthrone to Various Nitroalkenesa |
实验结果表明:催化剂1f能够顺利地催化不同取代硝基乙烯为底物的反应, 得到80%~97%的产率.并表现出优良的立体选择性(86%~99% ee), 其中以2-氟及3-甲基取代的底物获得了最高的对映体过量值(99%ee, entries 2, 7).
3 结论我们将硫脲衍生物用于有机催化蒽酮与硝基烯烃的不对称Michael加成反应, 筛选出最佳的催化体系, 并将其应用于13种硝基烯烃和蒽酮的反应, 均得到很好的化学产率和最高达99%ee的立体选择性.催化剂体系对该反应表现出优秀的普适性.
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