W. Weingärtner, G. Maas
FULL PAPER
The Eyring plot for the cycloaddition 3a + 7aǞ8a gave the follow-
ing equation: ln(k/T) = –4553/T + 4.1543 (R2 = 0.9867). The fol-
lowing activation parameters were obtained: ΔH‡ = 9.0 kcalmol–1,
(ATR): ν = 3052 (m), 1618 (m), 1593 (s), 1526 (m), 1480 (m), 1452
˜
(s), 1427 (m), 1343 (m), 1277 (w), 1163 (m), 1138 (s), 1074 (s), 885
(m), 849 (m), 787 (m), 767 (m), 737 (s) cm–1. C45H46BN3O (655.68):
calcd. C 82.43, H 7.07, N 6.41; found C 82.34, H 7.04, N 6.41.
‡
ΔS‡ = –39.0 calmol–1K–1, ΔG(298 K) = 20.7 kcalmol–1. The error
in ΔG is estimated to be Ϯ0.2 kcalmol–1 on the basis of possible
weighing errors.
N-(3-Azidopropyl)phthalimide (7b): Sodium azide (2.60 g,
40 mmol), NaI (4.50 g, 30 mmol), and N-(3-bromopropyl)phthal-
N,N,NЈ,NЈ,2-Pentamethyl-3-phenyl-2,3-dihydroisoxazole-4-carbox- imide (8.00 g, 30 mmol) were dissolved in acetone (10 mL) and the
amidinium Tetraphenylborate (5a): N-Methyl-C-phenylnitrone (4a,
54 mg, 0.40 mmol) was added to a suspension of N,N,NЈ,NЈ-tet-
solution was stirred for 24 h under reflux. The solvent was removed
in vacuo, the residue was dissolved in water (20 mL), and the crude
product was extracted with dichloromethane (3ϫ 10 mL). The
combined organic phases were washed with saturated aqueous
NaHCO3 solution, dried with MgSO4, and concentrated in vacuo
to yield colorless crystalline 7b (6.29 g, 91% yield); m.p. 64–65 °C.
1H NMR (400 MHz, CD3CN): δ = 1.90–1.97 (m, 2 H, CH2), 3.33–
3.36 (m, 2 H, CH2), 3.73–3.78 (m, 2 H, CH2), 7.67–7.72 (m, 2 H,
ramethylpropiolamidinium
tetraphenylborate
(3a,
172 mg,
0.39 mmol) in CHCl3 (1.5 mL). The suspension was stirred for 36 h
at ambient temperature. The solvent was then removed in vacuo,
and the residue was triturated several times with Et2O in an ultra-
sonic bath to afford pale yellow crude 5a. The solid was taken up
in CH2Cl2 and slowly precipitated by addition of Et2O at 0 °C. The
precipitate was dried in vacuo to afford 5a as a thermally sensitive,
off-white, crystalline powder (210 mg, 93% yield). The product un-
dergoes secondary reactions (isomerization, decomposition) above
ca. 40 °C. 1H NMR (400 MHz, CDCl3): δ = 2.95 (br. s, 12 H,
NCH3), 3.03 (s, 3 H, ONCH3), 5.08 (s, 1 H, 3-H), 6.84–6.87 (m, 4
H, HPh), 6.99–7.02 (m, 8 H, HPh), 7.32–7.35 (m, 9 H, HPh + 5-H),
7.41–7.44 (m, 5 H, HPh) ppm. 13C NMR (100 MHz, CD3CN): δ =
43.5 (NCH3), 48.1 (ONCH3), 75.2 (C-3), 107.9 (C-4), 123.2 (CPh),
127.0 (q, 3JB,C = 2.7 Hz, B-m-CPh), 127.7, 130.0, 130.6, 137.2, 140.6
H
Ph), 7.81–7.85 (m, 2 H, HPh) ppm. IR (KBr): ν = 2104 (s) cm–1.
˜
C11H10N4O2 (230.22): calcd. C 57.39, H 4.38, N 24.34; found C
57.29, H 4.37, N 24.32.
1-Benzyl-N,N,NЈ,NЈ-tetramethyl-1,2,3-triazole-4-carboxamidinium
Tetraphenylborate (8a): Benzyl azide (7a, 56 μL, 0.45 mmol) and
N,N,NЈ,NЈ-tetramethylpropiolamidinium tetraphenylborate (3a,
133 mg, 0.30 mmol) were placed in a Schlenk pressure tube and
heated in dry acetonitrile (2 mL) at 90 °C for 13 h (Method A);
alternatively, the reaction components were placed in a suitable re-
action vessel and exposed to microwave irradiation at 105 °C for
45 min (Method B). The solvent was removed in vacuo, and the
residue was triturated several times with diethyl ether in an ultra-
sonic bath. The crude product was recrystallized from EtOAc/pent-
ane to afford a beige powder (A: 141 mg, 82% yield; B: 154 mg,
1
(all CPh), 157.6 (C-5), 165.1 (q, JB,C = 49.5 Hz, BCPh), 165.3
(NC+N) ppm. IR (ATR): ν = 3053 (m), 3002 (w), 1597 (s), 1476
˜
(m), 1428 (m), 1402 (s), 1151 (m), 1112 (m), 1071 (m), 737 (s) cm–1.
C39H42BN3O (579.58): calcd. C 80.82, H 7.30, N 7.25; found C
80.41, H 7.34, N 7.29.
1
5-Cyclopropyl-N,N,NЈ,NЈ,2-pentamethyl-3-phenyl-2,3-dihydroisox-
azole-4-carboxamidinium Tetraphenylborate (5b): This compound
was synthesized as described for 5a from N,N,NЈ,NЈ-tetramethyl-3-
cyclopropylpropiolamidinium tetraphenylborate (3b, 189 mg,
89% yield); m.p. 159 °C (dec.). H NMR (400 MHz, CD3CN): δ =
3.12 (br. s, 12 H, NCH3), 5.65 (s, 2 H, CH2), 6.83–6.86 (m, 4 H,
HPh), 6.98–7.91 (m, 8 H, HPh), 7.26–7.29 (br. s, 8 H, HPh), 7.35–
1
7.44 (m, 5 H, HPh), 8.28 (s, 1 H, 5-H) ppm. H NMR (400 MHz,
0.39 mmol) to afford a pale yellow, crystalline powder (215 mg, CDCl3): δ = 2.74 (br. s, 12 H, NCH3), 5.22 (s, 2 H, PhCH2), 6.29
89% yield), which undergoes secondary reactions above ≈40 °C. 1H
(s, 1 H, 5-H), 6.85–6.89 (m, 4 H, HPh), 6.96–7.01 (m, 8 H, HPh),
NMR (400 MHz, CDCl3): δ = 1.09–1.15 (m, 1 H, HcPr), 1.19–1.26 7.14–7.16 (m, 2 H, HPh), 7.34–7.38 (m, 11 H, HPh) ppm. 13C NMR
(m, 4 H, HcPr), 2.17, 2.31, 2.65, 2.84 (4ϫs, each 3 H, NCH3), 2.92 (126 MHz, [D6]DMSO): δ = 43.0 (NCH3), 55.6 (CH2), 121.5 (CPh),
(s, 3 H, ONCH3), 4.75 (s, 1 H, 3-H), 6.86–6.90 (m, 4 H, HPh), 7.00– 125.3 (q, 3JB,C = 2.6 Hz, B-m-CPh), 128.1, 128.4, 129.0 (CPh), 131.4
7.04 (m, 8 H, HPh), 7.11–7.14 (m, 2 H, HPh), 7.36–7.41 (m, 11 H,
H
(C-5), 135.0 (CPh), 135.1 (C-4), 135.5 (CPh), 159.9 (NC+N), 163.3
1
Ph) ppm. 13C NMR (100 MHz, CD3CN): δ = 8.6, 9.5, 10.1 (all (q, JB,C = 49.5 Hz, BCPh) ppm. IR (ATR): ν = 3118 (m), 3057
˜
C
cPr), 42.7, 43.0, 43.3, 43.7 (all NCH3), 47.2 (ONCH3), 77.3 (C-3), (m), 2987 (w), 1621 (vs), 1575 (s), 1498 (m), 1458 (m), 1427 (m),
103.5 (C-4), 123.2 (CPh), 127.0 (q, 3JB,C = 2.7 Hz, B-m-CPh), 128.1,
1399 (s), 1242 (m), 1167 (m), 1133 (s), 1051 (s), 1033 (m), 878 (m),
1
+
130.1, 130.5, 137.2, 140.4 (all CPh), 165.2 (q, JB,C = 49.5 Hz,
846 (s) cm–1. HRMS [(+)-ESI-TOF]: calcd. for cation C14H20N5
BCPh), 166.1 (NC+N), 171.5 (C-5) ppm. IR (ATR): ν = 3052 (m),
258.1713; found 258.1721. C38H40BN5 (577.34): calcd. C 79.02, H
6.98, N 12.13; found C 78.83, H 7.01, N 12.01.
˜
3009 (w), 1612 (s), 1585 (s), 1524 (m), 1424 (s), 1397 (s), 1242 (w),
1165 (m), 1077 (m), 1044 (s), 908 (m), 778 (m), 735 (s) cm–1.
C42H46BN3O (619.64): calcd. C 81.41, H 7.48, N 6.78; found C
81.31, H 7.35, N 6.79.
1-Benzyl-5-cyclopropyl-N,N,NЈ,NЈ-tetramethyl-1,2,3-triazole-4-
carboxamidinium Tetraphenylborate (8b): This compound was syn-
thesized as described for 8a from N,N,NЈ,NЈ-tetramethyl-3-cyclo-
N,N,NЈ,NЈ,2-Pentamethyl-3,5-diphenyl-2,3-dihydroisoxazole-4-carb-
oxamidinium Tetraphenylborate (5c): This compound was synthe-
sized as described for 5a from N,N,NЈ,NЈ-tetramethyl-3-phenylpro-
piolamidinium tetraphenylborate (3c, 203 mg, 0.39 mmol) to afford
a white, crystalline powder (230 mg, 90% yield), which undergoes
secondary reactions above ca. 40 °C. 1H NMR (400 MHz,
propylpropiolamidinium
tetraphenylborate
(3b,
145 mg,
0.30 mmol; for reaction conditions see Table 1) to afford a yellow
powder (Method A: 142 mg, 77% yield; Method B: 146 mg, 79%
yield; Method C: 121 mg, 66%); m.p. 184–186 °C. 1H NMR
(500 MHz, CD3CN): δ = 0.51–0.55 (m, 2 H, HcPr), 1.03–1.07 (m,
2 H, HcPr), 1.64–1.67 (m, 1 H, HcPr), 2.93 (br. s, 6 H, NCH3), 3.38
CD3CN): δ = 2.36 (s, 3 H, NCH3), 2.79 (s, 6 H, NCH3), 3.11 (s, 3 (br. s, 6 H, NCH3), 5.67 (s, 2 H, CH2), 6.83–6.87 (m, 4 H, HPh),
H, ONCH3), 3.27 (s, 3 H, NCH3), 5.32 (s, 1 H, 3-H), 6.85–6.89 (m, 6.98–7.02 (m, 8 H, HPh), 7.23–7.42 (m, 13 H, HPh) ppm. 13C NMR
4 H, HPh), 7.00–7.04 (m, 8 H, HPh), 7.29–7.32 (m, 8 H, HPh), 7.43– (126 MHz, [D6]DMSO): δ = 3.45 (C-1cPr), 5.03 (C-2cPr), 42.7
3
7.76 (m, 10 H, HPh) ppm. 13C NMR (100 MHz, CD3CN): δ = 42.8,
(NCH3), 51.6 (CH2), 121.5 (CPh), 125.3 (q, JB,C = 2.3 Hz, B-m-
42.9, 43.2, 44.4 (4ϫNCH3), 47.0 (ONCH3), 78.6 (C-3), 102.7 (C- CPh), 127.7, 128.2, 128.8, 134.7, 135.1 (all CPh), 133.1 (C-4), 142.7
3
1
4), 123.2 (CPh), 127.0 (q, JB,C = 2.7 Hz, B-m-CPh), 127.7, 128.7,
(5-C), 159.6 (NC+N), 163.5 (q, JB,C = 49.3 Hz, BCPh) ppm. IR
129.1, 130.4, 130.6, 130.9, 134.3, 137.2, 139.2 (all CPh), 165.2 (q,
(ATR): ν = 3053 (m), 1625 (vs), 1586 (s), 1526 (m), 1477 (s), 1443
(m), 1428 (s), 1404 (m), 1354 (w), 1259 (m), 1167 (m), 1145 (m),
˜
1JB,C = 49.2 Hz, BCPh), 165.3 (NC+N), 169.3 (C-5) ppm. IR
6378
www.eurjoc.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2012, 6372–6382