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12 General experimental procedure for 6, 9, 10 and 12: A solution
of 2-nitro glycal (1 mmol) and Danishefky’s diene (1.1
mmol) in dry toluene (2 mL) was refluxed under argon for 36 h. The
reaction mixture was allowed to cool and the toluene was removed
under reduced pressure. Then a mixture of THF-10% H2SO4 in
H2O (2:1) was added and stirred at room temperature for
30 min. The product was isolated by extractive workup followed by
filtration by column chromatography. The hydrolyzed product was dissolved
in 1 M NaOCH3 in methanol (2
mL) and heated at 50 °C for 1.5 h. Methanol was evaporated
followed by neutralization with saturated aq NH4Cl solution
and extracted with ethyl acetate. The organic layer was washed with
water, brine and dried over anhydrous MgSO4. Evaporation
of the solvent yielded the benzannulated pyrans.
For compound 5: A mixture of hydrolyzed products 3 and 4 and DBN
(3 equiv) in toluene (2 mL) was refluxed for 24 h. The reaction
mixture was neutralized with aq NH4Cl after removal of
the toluene followed by extraction with ethyl acetate. The organic
layer was washed with dilute HCl, water, brine and dried over anhydrous
MgSO4. Evaporation of the solvent and purification by
column chromatography yielded the product 5 in
68% yield.
Some selected data:
5: [α]D
20 = -39.1
(c 1, CHCl3); 1H NMR (250 MHz): δ 2.86 (br
s, 1 H), 3.45-3.55 (m, 2 H), 3.59 (dd, J = 1.99,
7.82 Hz, 1 H), 3.93 (d, J = 10.8
Hz, 1 H), 4.09 (d, J = 10.8
Hz, 1 H), 4.19 (br s, 1 H), 4.25 (d, J = 11.46
Hz, 1 H), 4.44 (d, J = 11.46 Hz,
1 H), 4.43-4.54 (m, 3 H), 5.37 (br s, 1 H), 6.81-6.85
(m, 2 H), 6.93-6.97 (m, 2 H), 7.18-7.35 (m, 15
H). 13C NMR (62.9 MHz): δ 69.7,
70.4, 71.2, 73.3, 73.9, 80.3, 81.1, 115.4, 127.6, 127.7, 127.9,
128.2, 128.3, 129.1, 130.5, 137.5, 137.8, 156.1. MALDI: m/z 507 (M + Na+).
Calcd: C, 76.80; H, 6.66. Found: C, 76.55; H, 6.39.
6: [α]D
20 = +6.3
(c 1, CHCl3); 1H NMR (250 MHz): δ 3.71-3.83
(m, 2 H), 4.14 (dd, J = 2.2
Hz, 3.2 Hz, 1 H), 4.34 (td,
J = 1.4
Hz, 5.9 Hz, 1 H), 4.44 (d, J= 11.9
Hz, 1 H), 4.53 (d, J = 11.9
Hz, 1 H), 4.57-4.86 (m, 5 H), 5.14 (br s, 1 H), 6.29 (d, J = 2.4 Hz, 1 H), 6.39 (dd, J = 2.5 Hz, 8.3 Hz, 1 H), 7.20-7.40
(m, 16 H). 13C NMR (62.9 MHz): δ 69.1,
70.1, 71.8, 73.1, 73.5, 74.0, 75.8, 103.1, 108.6, 114.0, 127.7,
127.8, 128.1, 128.3, 128.4, 129.3, 137.7, 138.1, 153.9, 156.7. MALDI: m/z 505 (M + Na+).
Calcd: C, 77.16; H, 6.27. Found: C, 76.82; H, 6.57.
9: [α]D
20 = +26.7
(c 1, CHCl3); 1H NMR (250 MHz): δ 3.7-3.89
(m, 2 H), 4.04 (t, J = 6.1 Hz,
1 H), 4.29-4.35 (m, 1 H), 4.58-4.80 (m, 7 H),
5.4 (br s, 1 H), 6.34 (d, J = 2.43
Hz, 1 H), 6.4 (dd, J = 2.44
Hz, 8.34 Hz, 1 H), 7.1 (d, J = 8.38
Hz, 1 H), 7.23-7.37 (m, 15 H). 13C
NMR (62.9 MHz): δ 69.0, 71.2, 73.1, 73.5, 73.6, 76.1, 77.01,
103.3, 109, 113.9, 127.7, 127.9, 128.0, 128.5, 130.2, 137.8, 138.2,
154.6, 156.7. MALDI: m/z 505(M + Na+).
10: [α]D
20 = +30.1
(c 1, CHCl3); 1H NMR (250 MHz): δ 3.53-3.92
(m, 6 H), 4.35-4.92(m, 17 H), 5.18 (br s, 1 H), 5.34 (d, J = 3.6 Hz, 1 H), 6.37 (d, J = 2.18 Hz, 1 H), 6.42 (dd, J = 2.32 Hz, 8.24 Hz, 1 H),
7.12 (dd, J = 3.26 Hz, 7.06
Hz, 1 H), 7.24-7.30 (m, 30 H). 13C
NMR (62.9 MHz): δ 68.4, 69.0, 69.4, 70.9, 72.9, 73.3, 73.4,
74.5, 75.0, 75.5, 76.9, 80.0, 81.7, 96.1, 103.7, 109.1, 112.7, 127.6,
127.7, 127.8, 127.9, 128.3, 128.4, 131.1, 137.9, 138.0, 138.1, 138.3,
138.8, 154.9, 156.9. MALDI: m/z 937
(M + Na+).
12: [α]D
20 = -27.1
(c 1, CHCl3); 1H NMR (250 MHz): δ 1.46 (d, J = 6.48 Hz, 3 H), 3.69 (dd, J = 6.83 Hz, 8.08 Hz, 1 H), 4.11-4.19
(m, 1 H), 4.65-4.88 (m, 6 H), 6.27 (d, J = 2.48
Hz, 1 H), 6.40 (dd, J = 2.51
Hz, 8.39 Hz, 1 H), 7.15 (dd, J = 0.64 Hz,
8.41 Hz, 1 H), 7.23-7.36 (m, 10 H). 13C
NMR (62.9 MHz): δ 17.9, 71.5, 73.7, 74.4, 77.3, 79.1, 102.9,
109.0, 114.7, 127.7, 127.87, 127.89, 127.9, 128.5, 129.8, 137.8, 138.2,
155.0, 156.5. Cald: C, 76.57; H, 6.43. Found: C, 76.25; H, 6.32.
15: [α]D
20 = +53.6
(c 0.5, CHCl3); 1H NMR (600 MHz): δ 2.02,
2.12 (2 s, 6 H), 2.25-2.33 (m, 1 H), 2.4-2.5 (m,
1 H), 2.9 (t, J = 6.7 Hz, 1
H), 3.77 (s, 3 H), 4.2-4.35 (m, 3 H), 5.08-5.17
(m, 3 H), 5.8-5.9 (m, 1 H), 6.46 (d, J = 1
Hz, 1 H), 6.53 (dd, J = 2.5
Hz, 8.4 Hz, 1 H), 6.98 (d, J = 8.5
Hz, 1 H). 13C NMR (150.8 MHz): δ 20.8,
21.0, 38.4, 41.5, 55.3, 63.3, 68.0, 69.9, 101.2, 108.5, 118.0, 130.5,
134.8, 153.5, 159.4, 170.4, 170.7. Calcd: C, 64.66; H, 6.63. Found:
C, 64.95; H, 7.0.
17: [α]D
20 = +29.6
(c 1, CHCl3); 1H NMR (250 MHz): δ 1.98, 2.0,
2.1 (3 s, 9H), 2.77 (d, J = 6.9
Hz, 2 H), 3.75 (s, 3 H), 4.07 (dd, J = 6.8
Hz, 11.8 Hz, 1 H), 4.23 (dd, J = 4.6
Hz, 11.8 Hz, 1 H), 5.13-5.26 (m, 2 H), 6.92-7.2
(m, 4 H). 13C NMR (62.9 MHz): δ 20.6,
20.7, 21.0, 36.2, 62.2, 70.6, 72.0, 121.6, 130.2, 133.6, 149.6,
169.3, 170.0, 170.4.
13
Dufner G.
Ph.D.
Dissertation
Universität Konstanz;
Germany:
1997.
14
Iida H.
Tamazaki N.
Kibayashi C.
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Tabata N.
Nagamitsu T.
Tomoda H.
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