Helvetica Chimica Acta – Vol. 95 (2012)
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4.5. (1RS,2RS,3RS)-3-Methoxy-1,2-bis(trifluoromethyl)cyclobutane-1,2-dicarbonitrile (12(trans-1)).
This is the main constituent (52%) of the oil and crystals from (E)-9 and the unsaturated ether. The oil
was adsorbed by filter paper; repeated recrystallization of the solid from CH2Cl2/pentane and subsequent
sublimation at 358/0.05 Torr gave colorless prisms. M.p. 78.5 – 798 (sealed cap.). IR (KBr): 714s, 810w,
996m, 1077m, 1089m; 1136s, 1143s, 1198vs þ 1210vs (br.), 1285s (CꢁF, CꢁO str.), no C ꢂ N str. visible;
2845w (MeO), 2920w, 2950w (CꢁH, sharp). 1H-NMR (100 MHz, CDCl3, F-decoupled): 3.85 (s, MeO);
the ABX system of ring-H was simulated with the program LAME [32]: 3.32, 3.40 (AB, CH2(4)); 4.81 (X,
HꢁC(3)); 2JAB ¼ 13.8, 3JAX ¼ 9.1, 3JBX ¼ 8.9. 13C-NMR (50.3 MHz, 1H-decoupled): 36.6 (s, C(4)); 39.9 (q,
2
2J(C,F) ¼ 34, C(1)); 51.6 (q, J(C,F) ¼ 29, C(2)); 60.0 (s, MeO); 77 (C(3), overlap with CDCl3); 111.0,
111.3 (2s, 2 CN); 121.6 (q, 1J(C,F) ¼ 284, CF3); 122.4 (q, 1J(C,F) ¼ 283, CF3). 19F-NMR (CDCl3,
94.1 MHz): ꢁ 66.5 (br. s, 2-CF3); ꢁ 71.2 (br. s, 1-CF3); on 1H-decoupling 2 sharp s).
4.6. (1RS,2RS,3SR)-Isomer (12(trans-2)). The fraction of VPC was distilled at 608/0.1 Torr and
crystallized at 08. M.p. ca. 208. IR: 726m (sharp), 921m, 985m; 1057s (CꢁO); 1202vs þ 1262vs (br. (CꢁF,
CꢁO)), no C ꢂ N; 2850w, 2950w (CꢁH). 1H-NMR (CDCl3, 100 MHz, F-decoupled): 3.54 (s, MeO), ABX
2
system calc. with the method of effective Larmor frequencies [33]: 2.90, 3.06 (AB part, JAB ¼ 13.4,
HAꢁC(4), HBꢁC(4)); 4.49 (X, 3JAX ¼ 8.1, 3JBX ¼ 7.9, HꢁC(3)). 19F-NMR (CH2Cl2, 94.1 Hz): ꢁ 68.9 (br. s,
2-CF3), ꢁ 71.6 (s, structured, 1-CF3); (CDCl3): ꢁ 69.0 (br. s, 2-CF3), ꢁ 70.5 (d, partially resolved,
5J(F,F) ¼ 1.5, 1-CF3).
4.7. (1RS,2SR,3SR)-Isomer (12(cis-1)). The colorless leaflets, obtained by VPC, were sublimed at
408/0.05 Torr. M.p. 78.0 – 78.58 (pentane). IR: 731m, 747m, 993m, 1030m, 1043m (all sharp); 1174s,
1183m, 1193s, 1202s, 1238m, 1261s, 1303s (all CꢁO, CꢁF str.); 2255vw (C ꢂ N non-conjug.), 2840vw (CꢁH
1
of MeO); 2950w, 2980w, 3035w (CꢁH, sharp). H-NMR (CDCl3, 100 MHz, F-decoupled): 3.02 (br. d,
3
4
3J(3,4) ¼ 9.0, CH2(4)); 3.60 (s, MeO); 4.69 (t, J(3,4) ¼ 9.0, HꢁC(3)); (F-coupled): 3.02 (dq, J(H,F) ¼
0.9, CH2(4)); 4.69 (tq, 4J(H,F) ¼ 1.9, HꢁC(3)). 13C-NMR (CDCl3, 50.3 MHz, 1H-decoupled): 36.2 (s,
2
2
C(4)); 42.3 (q, J(C,F) ¼ 30, C(1)); 53.6 (q, J(C,F) ¼ 31, C(2)); 59.9 (s, MeO); 77 (below CꢁD signals,
C(3)); 112.4 (q, 3J(C,F) ¼ 3.5, CN); 113.4 (q, 3J(C,F) ¼ 1.5, CN); 120.6 (q, 1J(C,F) ¼ 281, CF3); 121.1 (q,
1J(C,F) ¼ 284, CF3). 19F-NMR (CDCl3, H-decoupled): ꢁ 62.9 (br. q, J(F,F) ¼ 11.0, 2-CF3); ꢁ 68.9 (q,
1
5
5J(F,F) ¼ 11.4, 1-CF3).
4.8. (1RS,2SR,3RS)-Isomer (12(cis-2)). Distillation of the product (288 mg), which was obtained
from (E)-9 and methyl vinyl ether in MeCN, furnished oil and crystals, which were separated by filter
paper. Colorless needles (23 mg) were obtained from pentane. M.p. 77.5 – 78.08. IR: 720m, 743m, 985s,
1043m (all sharp); 1109s, 1179vs þ 1220vs (br.), 1290s (br., CꢁO, CꢁF), 2255vw (C ꢂ N, uncertain).
1H-NMR (CDCl3, 100 MHz, 19F-decoupled): 3.82 (s, MeO); ABX calc. with effective Larmor frequencies
[33]: 3.26, 3.35 (AB, JAB ¼ 13.4, CH2(4)); 4.73 (X, 3J(3,4A) ¼ 8.8, 3J(3,4B) ¼ 7.7, HꢁC(3)); (fully
6
coupled): 33.0, 33.2 (2 apparent dqq, J(H,F) ¼ 0.8 and 0.6, CH2(4)); 3.82 (q, J(H,F) ¼ 0.3, MeO); 4.74
(apparent tq, 4J(H,F) ¼ 0.8, HꢁC(3)). 13C-NMR (CDCl3, 50.3 MHz, 1H-decoupled): 35.4 (s, C(4)); 41.4
2
2
(q, J(C,F) ¼ 37, C(1)); 57.3 (q, J(C,F) ¼ 37, C(2)); 58.7 (s, MeO); 73.1 (s, C(3)); 109.9, 112.1 (br. 2s,
2 CN); 120.3 (q, 1J(C,F) ¼ 276, CF3); 121.9 (q, 2J(C,F) ¼ 281, CF3). 19F-NMR (CDCl3, 50.3 MHz, H-
decoupled): ꢁ 67.9, ꢁ 68.8 (2q, 5J(F,F) ¼ 11.4, further split, 2 CF3); (CH2Cl2): ꢁ 67.8, ꢁ 68.8 (2q,
5J(F,F) ¼ 11.2, 2 CF3).
4.9. Equilibration of Cyclobutanes 12. LiClO4 (p.a.) was dried at 1608/0.3 Torr for 4 h and dissolved in
abs. Et2O. The 2m soln. (0.5 ml) and the diastereoisomers of 12 (114 mg, ca. 0.40 mmol, obtained with
(E)-9), in a sealed NMR tube, were heated in a thermostat at 708; in a second tube, a specimen of 12,
prepared from (Z)-9, was treated correspondingly with 2m LiClO4. Fig. 2 shows the slow isomerization;
after 143 d, the two isomer mixtures have become identical within the limits of the 19F-NMR analysis. No
BTE signals were observed. Beginning decomposition was noticed after 160 d.
5. (2 þ 2) Cycloadditions of BTE (9) with Ethyl Vinyl Ether. 5.1 (E)-9. The procedure was similar to
that described above; a brief description of one example would be sufficient. Ethyl vinyl ether (70 mg,
0.97 mmol) and (E)-9 (246 mg, 1.15 mmol) in CH2Cl2 (4 ml) showed a light-yellow CT complex color
which slowly faded. After 8 d at r.t., the solvent was removed, and distillation at 558/0.3 Torr furnished 13
as a colorless oil (248 mg, 89%); Table 2 shows the ratio of the four diastereoisomers. The quant. 19F-
NMR analysis was based on the following signals: ꢁ 71.6, ꢁ 66.4 (2s) for 13(trans-1), ꢁ 70.3 (s) for
13(trans-2), ꢁ 62.7 (q) for 13(cis-1), and ꢁ 67.7 (q) for 13(cis-2). As described above, the elemental