Tin-Mediated Free-Radical Cyclization of β-Allenylbenzoyloximes
3,3,6-Trimethylhepta-4,5-dien-2-one O-Benzoyloxime (5f): 76%
FULL PAPER
4-(Benzoyloxyamino)-3,3,4,5,5-pentamethyl-1-(tri-n-butylstannyl)-
cyclopentene (7f): Obtained from 5f in 75% yield, colourless oil. Ϫ
yield, white crystals (pentane), m.p. 47Ϫ48°C. Ϫ IR (KBr): ν˜ ϭ
1
1967 cmϪ1 (CϭCϭC), 1745 (CϭO). Ϫ H NMR (200 MHz): δ ϭ IR (CCl4): ν˜ ϭ 1751 cmϪ1 (CϭO). 1H NMR (200 MHz): δ ϭ
1.32 [s, 6 H, C(CH3)2], 1.71 [d, J ϭ 2.8 Hz, 6 H, (CH3)2CϭC], 2.04
0.83Ϫ0.93 (m, 15H, SnCH2CH2CH2CH3), 1.08 (s, 3 H, CH3), 1.09
(s, 3 H, CH3CϭN), 4.99 (sept, J ϭ 2.8 Hz, 1 H, CHϭC), 7.44Ϫ7.56 (s, 3 H, CH3), 1.16 (s, 3 H, CH3), 1.18 (s, 3 H, CH3), 1.19 (s, 3 H,
(m, 3 H, Ph), 8.02Ϫ8.07 (m, 2 H, Ph). Ϫ 13C NMR (50 MHz): δ ϭ CH3), 1.24Ϫ1.52 (m, 12 H, SnCH2CH2CH2CH3), 5.44 (s, 1 H,
13.1 (NϭCCH3), 20.4 (CH3), 25.4 (CH3), 42.7 [C(CH3)2], 96.2 (Cϭ
CϭCH), 98.4 (CϭCϭCH), 128.4 129.4 and 133.0 (CH, Ph), 163.8
CHϭC), 7.39Ϫ7.56 (m, 3 H, Ph), 7.95Ϫ8.00 (m, 2 H, Ph), 8.04 (s,
1 H, Ph). Ϫ 13C NMR (50 MHz): δ ϭ 10.0 (SnCH2), 13.7
(CϭO), 171.7 (CϭN), 201.0 (CϭCϭCH). Ϫ C17H21NO2 (271.36): (SnCH2CH2CH2CH3), 18.8 (CH3), 25.5 (CH3), 26.2 (CH3), 27.4
calcd. C 75.25, H 7.80, N 5.16; found C 75.24, H 7.68, N 5.14.
(CH2), 29.2 (CH2), 52.1 [C(CH3)2], 56.3 [C(CH3)2], 70.7 (CHNH),
128.6 129.2 and 133.1 (CH, Ph), 128.7 (C, Ph), 148.5 (CHϭC),
150.4 (CHϭC), 166.4 (CϭO). Ϫ C29H49NO2Sn (562.41): calcd. C
61.93, H 8.78, N 2.49; found C 61.85, H 8.83, N 2.45.
2,2,5-Trimethyl-1-phenylhexa-3,4-dienone O-Benzoyloxime (5j):
66% yield, white needles (pentane), m.p. 104Ϫ106°C. Ϫ IR (KBr):
1
ν˜ ϭ 1965 cmϪ1 (CϭCϭC), 1753 (CϭO). Ϫ H NMR (200 MHz):
δ ϭ 1.38 [s, 6 H, C(CH3)2], 1.59 [d, J ϭ 2.8 Hz, 6 H, (CH3)2CϭC],
5.12 (sept, J ϭ 2.8 Hz, 1 H, CHϭC), 7.15Ϫ7.60 (3 m, 10 H, Ph).
Ϫ
Cyclization of 5i gave a mixture of 6i and 7i.
13C NMR (50 MHz): δ ϭ 20.2 (CH3), 26.1 (CH3), 42.7
[C(CH3)2], 96.2 (CϭCϭCH), 98.7 (CϭCϭCH), 127.2 127.7 128.2
128.3 129.2 and 129.4 (CH, Ph), 132.9 and 133.5 (C, Ph), 163.7
(CϭO), 174.0 (CϭN), 201.4 (CϭCϭCH). Ϫ C22H23NO2 (333.43):
calcd. C 79.25, H 6.95, N 4.20; found C 79.18, H 6.95, N 4.12.
2,2-Dimethyl-1-phenyl-4-(tri-n-butylstannyl)hex-3-enone O-Benzoyl-
oxime (6i): 19% yield, colourless oil. Ϫ IR (CCl4): ν˜ ϭ 1719 cmϪ1
(CϭO). Ϫ 1H NMR (400 MHz): δ ϭ 0.80Ϫ1.00 (m, 15H,
SnCH2CH2CH2CH3), 1.02 (t,
J ϭ 7.5 Hz, 3 H, CH2CH3),
1.24Ϫ1.33 (m, 6 H, CH2), 1.41Ϫ1.47 (m, 6 H, CH2), 1.50 [s, 6 H,
C(CH3)2], 2.62 (qd, J ϭ 7.5 Hz and 2.2 Hz, 2 H, CH2CH3), 5.30
(d, J ϭ 2.2 Hz, 1 H, CHϭC), 7.17Ϫ7.62 (m, 10 H, Ph). Ϫ 13C
NMR (100 MHz): δ ϭ 10.1 (SnCH2), 13.7 (SnCH2CH2CH2CH3),
14.7 (CH3), 26.8 (CH2), 27.4 (CH2), 28.4 (CH3), 29.1 (CH2), 44.9
[C(CH3)2], 127.5 127.6 128.3 129.4 and 132.8 (CH, Ph), 129.3 and
134.0 (C, Ph), 142.3 (CHϭC), 153.8 (CHϭC), 163.8 (CϭO), 173.8
(CϭN). Ϫ C33H49NO2Sn (610.45): calcd. C 64.93, H 8.09, N 2.29;
found C 65.01, H 8.11, N 2.26.
1-Diethylphosphonato-2,2,5-trimethylhexa-3,4-dienone O-Ben-
zoyloxime (5m): 23% yield, colourless oil. Ϫ H NMR (200 MHz):
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δ ϭ 1.22 (t, J ϭ 7.0 Hz, 6 H, OCH2CH3), 1.46 [s, 6 H, C(CH3)2],
1.67 [d, J ϭ 2.8 Hz, 6 H, (CH3)2CϭC], 4.13 (m, 4 H, OCH2CH3),
5.40 (m, J ϭ 2.8 Hz, 1 H, CHϭC), 7.40Ϫ7.56 (m, 3 H, Ph),
8.14Ϫ8.19 (m, 2 H, Ph). Ϫ 13C NMR (50 MHz): δ ϭ 16.3 and
16.4 (OCH2CH3), 18.6 (CH3), 26.5 (CH3), 26.6 CH3), 43.3 (d, J ϭ
21.1 Hz, [C(CH3)2], 62.6 and 62.7 (OCH2CH3), 95.5 (CϭCϭCH),
98.7 (CϭCϭCH), 128.6 130.1 and 133.5 (CH, Ph), 134.6 (C, Ph),
163.2 (CϭO), 166.8 (d, J ϭ 141.9 Hz, CϭN), 201.6 (CϭCϭCH).
Ϫ C20H28NO5P (393.42): calcd. C 61.06, H 7.17, N 3.56; found C
61.00, H 7.11, N 3.47.
4-(Benzoyloxyamino)-3,3,5-trimethyl-4-phenyl-1-(tri-n-butyl-
stannyl)cyclopentene (7i): 44% yield, pale yellow oil. Ϫ IR (CCl4):
ν˜ ϭ 1720 cmϪ1 (CϭO). Ϫ The 1H-NMR and 13C-NMR spectra
were recorded on a mixture of both isomers (9:1 ratio). Only the
major isomer could be fully described. Major isomer: 1H NMR
(200 MHz): δ ϭ 0.56 (s, 3 H, CH3), 0.85Ϫ0.96 (m, 15 H,
SnCH2CH2CH2CH3), 1.19 [d, J ϭ 7.4 Hz, 3 H, CH(CH3)],
1.21Ϫ1.36 (m, 6 H, CH2), 1.35 (s, 3 H, CH3), 1.37Ϫ1.51 (m, 6 H,
CH2), 3.77 [qd, J ϭ 7.4 Hz and 2.3 Hz, 1 H, CH(CH3)], 5.70 (d,
J ϭ 2.3 Hz, 1 H, CHϭC), 7.25Ϫ7.79 (3m, 10 H, Ph), 8.16 (s, 1 H,
General Procedure for the Tin-Mediated Radical Cyclization of the
Compounds 5a؊d (Table 1): A hexane solution of Et3B (1.0 ,
1.0 mL, 1.0 mmol) and 20 mL of air were added portionwise for 48
h to a solution of tin hydride (1.2 mmol) and 5a؊d (1.0 mmol) in
cyclohexane (50 mL) under argon. The solvent was evaporated un-
der reduced pressure and the crude mixture was purified by silica-
gel column chromatography (eluent: Et2O/pentane).
NH).
Ϫ δ ϭ 9.6 (SnCH2), 13.8
13C NMR (50 MHz):
4-(Benzoyloxyamino)-3,3,5,5-tetramethyl-1-(tri-n-butylstannyl)
cyclopentene (7b): 75% yield, colourless oil. Ϫ IR (CCl4): ν˜ ϭ 1721
cmϪ1 (CϭO). Ϫ 1H NMR (200 MHz): δ ϭ 0.83Ϫ0.96 (m, 15 H,
SnCH2CH2CH2CH3), 1.08 (s, 3 H, CH3), 1.11 (s, 3 H, CH3), 1.22
(s, 3 H, CH3), 1.24 (s, 3 H, CH3), 1.26Ϫ1.54 (m, 12 H,
SnCH2CH2CH2CH3), 3.25 (d, J ϭ 7.4 Hz, 1 H, CHNH), 5.48 (s,
1 H, CHϭC), 7.41Ϫ7.57 (m, 3 H, Ph), 8.00Ϫ8.05 (m, 2 H, Ph),
8.18 (d, J ϭ 7.4 Hz, 1 H, CHNH). Ϫ 13C NMR (50 MHz): δ ϭ
9.7 (SnCH2), 13.7 (SnCH2CH2CH2CH3), 23.3 (CH3), 24.0 (CH3),
27.4 (CH2), 29.2 (CH2), 30.2 (CH3), 31.1 (CH3), 49.2 [C(CH3)2],
53.3 [C(CH3)2], 77.0 (CHNH), 128.6 129.2 and 133.2 (CH, Ph),
128.7 (C, Ph), 148.8 (CHϭC), 151.1 (CHϭC), 166.5 (CϭO). Ϫ
C28H47NO2Sn (548.38): calcd. C 61.33, H 8.64, N 2.55; found C
61.38, H 8.59, N 2.54.
(SnCH2CH2CH2CH3), 15.5 (CH3), 22.7 (CH3), 26.2 (CH3), 27.4
(CH2), 29.3 (CH2), 51.1 (CH), 53.3 [C(CH3)2], 76.9 (CNH), 127.1
127.6 128.0 128.4 129.2 and 132.9 (CH, Ph), 128.9 and 140.5 (C,
Ph), 145.1 (CHϭC), 150.1 (CHϭC), 165.7 (CϭO). Ϫ Minor iso-
1
mer: H NMR (200 MHz) (incomplete description): δ ϭ 3.26 [qd,
J ϭ 7.2 Hz and 2.8 Hz, 1 H, CH(CH3)], 5.82 (d, J ϭ 2.8 Hz, 1 H,
CHϭC). Ϫ 13C NMR (50 MHz) (incomplete description): δ ϭ 9.8
(SnCH2), 13.8 (SnCH2CH2CH2CH3), 27.4 (CH2), 29.3 (CH2), 54.3
(CH), 78.8 (CNH), 133.2 (CH, Ph), 139.8 (C, Ph), 146.6 (CHϭC),
152.4 (CHϭC), 166.3 (CϭO). Ϫ C33H49NO2Sn (610.45): calcd. C
64.93, H 8.09, N 2.29; found C 64.89, H 8.06, N 2.26.
Cyclization of 5j afforded a mixture of 8j, 9j, and 10j.
General Procedure for the Tin-Mediated Radical Cyclization of the
Compounds 5e؊m (Tables 1 and 2): Bu3SnH (1.2 equiv.) and AIBN
(0.2 equiv.) were added to a cyclohexane solution (0.02 ) of the
compounds 5e؊m. After this solution was degassed with a stream
2,2,5,5-Tetramethyl-6-phenyl-3-(tri-n-butylstannyl)-2,5-dihydro-
pyridine (8j): 82% yield, colourless oil. Ϫ IR (CCl4): ν˜ ϭ 1679 cmϪ1
(CϭN). Ϫ 1H NMR (400 MHz): δ ϭ 0.88Ϫ0.97 (m, 15H,
SnCH2CH2CH2CH3), 1.14 (s, 6 H, CH3), 1.31Ϫ1.38 (m, 6 H, CH2),
of argon, the mixture was heated under reflux, and monitored by 1.32 (s, 6 H, CH3), 1.47Ϫ1.55 (m, 6 H, CH2), 5.55 (s, 1 H, CHϭ
TLC until the starting material had disappeared. After evaporation
of the solvent, the crude mixture was purified by silica-gel column
chromatography (Et2O/pentane starting from 5e؊l; CH2Cl2/ethyl
acetate starting from 5m).
C), 7.30 (m, 5 H, Ph). Ϫ 13C NMR (100 MHz): δ ϭ 10.5 (SnCH2),
13.7 (SnCH2CH2CH2CH3), 27.4 (CH2), 28.7 (CH3), 29.1 (CH2),
32.0 (CH3), 35.0 (CϪCϭN), 60.5 (CϪNϭC), 127.6 127.8 and 127.9
(CH, Ph), 141.2 (C, Ph), 141.7 (CHϭC), 144.3 (CHϭC), 171.1 (Cϭ
Eur. J. Org. Chem. 2000, 275Ϫ280
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