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<A NAME="RD14502ST-5">5</A>
Typical Procedure
for Silyloxypyrroles 5.
To a solution of 2,5-dimethoxy-2,5-dihydrofuran
(1 equiv) and chiral amine 4a,c-e (1
equiv) in water (0.25 M) was added a concd solution of HCl (1.5
equiv). The mixture was stirred at r.t. for 3 h then neutralized
with solid NaHCO3 and extract with CH2Cl2.
The combined organic layers were dried over MgSO4 and
the solvent distilled off. A red oil, mixture of the α,β and β,γ unsaturated
lactams was then obtained. tert-Butyldimethylsilyl
triflate (1 equiv) was slowly added to a solution of either the
crude product or the purified lactams (1 equiv) and NEt3 (2
equiv) in CH2Cl2 (0.1 M) and the mixture was
stirred at r.t. for 1 h. The solvent was evaporated under vacuum
and the residue purified by filtration on a pad of alumina with
a mixture of heptane and EtOAc. (Nota: silyloxypyrroles are used
to be kept under argon at -20 °C). Analyses for 5d: [α]D
25 +11.7
(c 0.69, CH2Cl2).
Mp = 97 °C (heptane-EtOAc).
IR (KBr): ν = 2929, 2858, 1560,
1492, 1438 cm-1. 1H
NMR (300 MHz, CDCl3): δ = -0.05
(s, 3 H), 0.23 (s, 3 H), 0.80 (s, 9 H), 1.89 (d, J = 7.0
Hz, 3 H), 5.31 (dd, J = 2.0,
3.6 Hz, 1 H), 6.01 (t, J = 3.5
Hz, 1 H), 6.16 (q, J = 7.0
Hz, 1 H), 6.35 (dd, J = 1.9, 3.4
Hz, 1 H), 7.10 (d, J = 7.2
Hz, 1 H), 7.42 (t, J = 7.9
Hz,
1 H), 7.50-7.55 (m, 2 H), 7.77 (d, J = 8.3 Hz,
1 H), 7.88 (d, J = 7.4
Hz, 1 H), 8.08 (d, J = 8.0
Hz, 1 H). 13C NMR
(75 MHz,
CDCl3): δ = -5.0, -4.6,
18.2, 21.4, 25.7, 49.5, 87.7, 105.2, 109.8, 123.2, 125.8, 126.5,
128.1, 129.1, 131.0, 134.1, 139.7, 142.2. HRMS (CI, NH3): m/z calcd for C22H30NOSi
(MH+): 352.2097. Found: 352.2101. Typical Procedure for Cyclobutanols 6. To
a solution of silyloxypyrrole 5a-e (1 equiv) in anhyd CH2Cl2 (0.15
M) with 3Å MS, under argon, was added cyclobutanone (or cyclopentanone)
(1.6 equiv). After 15 min at r.t., the solution was cooled at -78 °C
and BF3·OEt2 (1.5 equiv) was added
in the course of 15 min. The solution was stirred at -78 °C
for 2 h and allowed to warm to 0 °C. The reaction
was quenched by addition of H2O, the aq phase was separated
and extracted with CH2Cl2. The organic phases
were combined, dried over Na2SO4 and the solvent
was removed under vacuum. The resulting oil was purified by flash
chromatography.
Analyses for 6d: Minor
diastereoisomer: [α]D
25 -264.1
(c 0.52, CHCl3). Mp = 245 °C
(CH2Cl2). IR (KBr): ν = 3388, 2976,
2937, 1660 cm-1. MS (CI, NH3): m/z = 308
(MH+), 238 (MH+ - C4H6O). 1H
NMR (300 MHz, CDCl3): δ = 0.35-0.5
(m, 1 H), 1.01 (s, 1 H, D2O exch.), 1.35-1.55
(m, 2 H), 1.55-1.70 (m, 2 H), 1.78 (d, J = 7.1
Hz, 3 H), 1.85-2.00 (m,
1 H), 4.25 (t, J = 1.6 Hz,
1 H), 6.30 (m, 2 H), 6.94 (dd, J = 7.0,
6.0 Hz, 1 H), 7.40-7.60 (m, 4 H), 7.83 (d, J = 8.1 Hz, 1
H), 7.90 (d, J = 8.3
Hz, 1 H), 8.23 (d, J = 8.4
Hz, 1 H). 13C NMR (75 MHz, DMSO): δ = 17.7,
24.4, 36.2, 40.6, 55.1, 74.8, 81.3, 128.5, 130.3, 130.8, 131.7,
132.9, 134.3, 134.5, 136.1, 139.0, 143.5, 151.3, 177.6. Major diastereoisomer: [α]D
25 -13.8
(c 0.97, CHCl3). Mp = 196-198 °C
(Et2O). IR (KBr): ν = 3382,
2977, 2934, 1658, 1394 cm-1. MS (CI, NH3): m/z = 308
(MH+), 238 (MH+ - C4H6O). 1H
NMR (300 MHz, CDCl3): δ = 1.36
(m, 1 H), 1.80-2.10 (m, 5 H), 1.75 (s, 1 H), 1.86 (d, J = 7.0 Hz,
3 H), 3.51 (t, J = 1.5
Hz, 1 H), 6.07 (q, J = 7.0
Hz, 1 H), 6.28 (dd, J = 1.6,
6.0 Hz, 1 H), 6.81 (dd, J = 1.8,
6.0 Hz, 1 H), 7.47 (m, 3 H), 7.63 (m, 2 H), 7.84 (m, 2 H). 13C
NMR (75 MHz, CDCl3): δ = 13.6,
19.1, 31.9, 36.2, 49.0, 69.6, 75.9, 123.2, 125.2, 125.8, 126.1,
127.3, 128.5, 129.1, 129.2, 132.0, 134.0, 136.2, 145.7, 173.3. Anal. Calcd
for C20H21NO2: C, 78.15; H, 6.89;
N, 4.56. Found: C, 78.03; H, 7.06; N, 4.60.
<A NAME="RD14502ST-6">6</A>
The crystal structure has been deposited
at the Cambridge Crystallographic Data Centre; deposition number
CCDC 180815.
<A NAME="RD14502ST-7A">7a</A>
Kuehne ME.
Matson PA.
Bornmann WG.
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Ishibashi H.
Fuke Y.
Yamashita T.
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<A NAME="RD14502ST-8">8</A>
Typical Procedure
for Spiro Compounds 7.
To a solution of cyclobutanol 6a-e (1
equiv) in CH2Cl2 (0.05 M) was added concd
aq HCl (1.5 equiv). After 9 h at 0 °C, the solvent
was removed under vacuum. The crude product was redissolved twice
in CH2Cl2 and reevaporated to eliminate trace
amount of acid.
Analyses for 7d (cristallyzed
from Et2O): [α]D
25 -48.4
(c 1.04, CHCl3). Mp = 140 °C
(Et2O). IR (KBr): ν = 2968, 1750,
1679, 1380, 1347, 780 cm-1. MS (CI,
NH3): m/z = 308 (MH+). 1H
NMR (400 MHz, CDCl3): δ = 1.07-1.17
(m, 2 H), 1.34-1.55 (m, 2 H), 1.62 (ddd, J = 6.5,
8.5, 12.3 Hz,
1 H), 1.67 (d, J = 7.0
Hz, 3 H), 1.87 (ddd, J = 9.5,
11.6, 18.9 Hz, 1 H), 1.93 (ddd, J = 6.8,
8.9, 12.3 Hz, 1 H), 2.23 (dd, J = 6.1,
18.9 Hz, 1 H), 2.43 (dd, J = 6.8,
8.5, 16.8 Hz, 1 H), 2.53 (ddd, J = 6.5,
8.9, 16.8 Hz, 1 H), 6.25 (q, J = 7.1
Hz,
1 H), 7.30-7.60 (m, 4 H), 7.83 (d, J = 9.7 Hz,
1 H), 7.79 (d, J = 7.6
Hz, 1 H), 8.00 (d, J = 8.3
Hz, 1 H). 13C NMR (75 MHz, CDCl3): δ = 7.8,
18.9, 29.0, 31.7, 32.3, 35.7, 47.5, 72.3, 124.0, 125.1, 125.9, 126.3,
127.2, 129.1, 129.3, 132.7, 133.9, 136.1, 175.7, 217.0. Anal. Calcd
for C20H21NO2: C, 78.15; H, 6.89;
N, 4.56. Found: C, 77.96; H, 7.15; N, 4.41.
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Kastsuki T.
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