6 5fa 7-F/Bn/MeO (1f) 71 >95:5 93:7
7 5ga 7-Br/Bn/MeO (1g) 64 >95:5 89:11
8 5ha H/p-MeC6H4CH2/MeO (1h) 68 >95:5 94:6
9 5ia H/p-BrC6H4CH2/MeO (1i) 69 >95:5 97:3
10 5ja H/m-ClC6H4CH2/MeO (1j) 73 >95:5 96:4
11 5ka H/o-ClC6H4CH2/MeO (1k) 62 >95:5 95:5
12 5la H/Ph/MeO (1l) 71 >95:5 96:4
13 5ma H/Bn/PhO (1m) 67 >95:5 91:9
14 5na H/Bn/Me (1n) 71 >95:5 92:8
15 5oa H/Bn/F (1o) 76 >95:5 87:13
aUnless otherwise indicated, the reaction was carried out at 0.1 mmol scale in toluene (1 mL) with MgSO4 (100 mg) for 48 h, and the mole ratio of 1:2a:3 was 1:1.2:1.1. bIsolated yield. cThe dr value was determined by 1H NMR. dThe er value was determined by HPLC.
接下来,在最优条件下,我们对芳香醛2进行了底物拓展(Table 2)。显然,这一反应适合缺电子的芳香醛(entries 1-7),这些缺电子的芳醛参与反应后,可得到相应的环化产物5,且具有可观的收率(52% to 72%),和较高的非对映选择性和对映选择性(>95:5 dr, 88:12 to 95:5 er)。相反,电中性的苯甲醛2h在反应中却表现出了较低的反应活性和对映选择性(entry 8)。此外,富电子的芳香醛2i-2j未能产生相应的产物5ai和5aj(entries 10-11)。这些结果都表明,醛的电子效应对于该1,3-偶极环加成反应,不管是反应活性还是反应对映选择性,都有着显著的影响。
Table 2 Substrate scope of aromatic aldehydes 2a
表2 芳香醛2的拓展a
entry 5 R (2) yield (%)b drc erd
1 5aa 4-NO2 (2a) 72 >95:5 95:5
2 5ab 4-CN (2b) 62 >95:5 89:11
3 5ac 4-CO2Me (2c) 62 >95:5 92:8
4 5ad 3-CN (2d) 52 >95:5 88:12
5 5ae 3-CF3 (2e) 60 >95:5 93:7
6 5af 3-F,4-Cl (2f) 65 >95:5 90:10
7 5ag 3-Cl,4-F (2g) 71 >95:5 88:12
9 5ah H (2h) 43 >95:5 72:28
10 5ai 3-Me (2i) trace - -
11 5aj 4-Me (2j) trace - -
a Unless otherwise indicated, the reaction was carried out at 0.1 mmol scale in toluene (1 mL) with MgSO4 (100 mg) for 48 h, and the mole ratio of 1a:2:3 was 1:1.2:1.1. bIsolated yield. cThe dr value was determined by 1H NMR. dThe er value was determined by HPLC.
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