UV spectrum (EtOH, λmax, nm, log ε): 221 (4.52), 287 (4.39), 321 (4.32).
PMR spectrum (300 MHz, DMSO-d , δ, ppm, J/Hz): 1.43 (6H, s, two CH -2), 2.00 (2H, m, CH -8), 2.64 (2H, m,
6
3
2
CH -9), 2.74 (2H, s, CH -3), 3.15 (2H, m, CH -7), 3.90 (1H, s, OCH -10), 6.47 (1H, s, H-11).
2
2
2
3
4-Hydroxy-10-methoxy-2,2-dimethyl-3,4,8,9-tetrahydrocyclopenta[c]pyrano[2,3-h]chromen-6-one (18). Asolution
of 17 (1.14 g, 4 mmol) in CH OH (10 mL) was treated in portions with NaBH (0.46 g, 12 mmol). The reaction mixture was
3
4
held at room temperature and stirred vigorously for 2 h (end of reaction determined using TLC). After the reaction was
complete, the mixture was poured into saturated NaCL solution (100 mL) and extracted with ethylacetate (3×20 mL). The
organic layer was dried over anhydrous MgSO . The solvent was removed in vacuum in a rotary evaporator. The solid was
4
-1
crystallized from CH OH. Yield 89%, mp 243-244°C, empirical formula C H O . IR spectrum (KBr, cm ): 3460, 2976,
3
18 20 5
1
706, 1692, 1620, 1592, 1488, 1440, 1392, 1372, 1324, 1244, 1204, 1156, 1130, 1090. UV spectrum (EtOH, λmax, nm,
log ε): 212 (4.71), 252 (4.11), 262 (4.12), 329 (4.36).
PMR spectrum (300 MHz, DMSO-d , δ, ppm, J/Hz): 1.38, 1.43 (6H, two s, two CH -2), 1.86 (1H, dd, J = 12.0,
6
3
J = 5.7, H-3α), 2.00 (2H, m, CH -8), 2.04 (1H, dd, J = 12.0, J = 2.4, H-3β), 2.64 (2H, m, CH -9), 3.17 (2H, m, CH -9), 3.80
2
2
2
(
1H, s, OCH -10), 4.88 (1H, m, H-4), 4.97 (1H, d, J = 5.4, OH-4), 6.24 (1H, s, H-11).
3
1
0-Methoxy-2,2-dimethyl-8,9-dihydrocyclopenta[c]pyrano[2,3-h]chromen-6-one (19). A solution of 18 (0.86 g,
3
mmol) in dioxane (10 mL) was treated with HCl (4 M, 10 mL). The reaction mixture was held at room temperature and
vigorously stirred for 4 h (end of reaction determined using TLC). After the reaction was complete, solvent was removed in
vacuum in a rotary evaporator. The solid was crystallized from CH OH. Yield 86%, mp 219-220°C, empirical formula
3
-1
C H O . IR spectrum (KBr, cm ): 1712, 1618, 1590, 1488, 1452, 1436, 1360, 1228, 1198, 1152, 1130, 1114, 1084.
18 18 4
UV spectrum (EtOH, λmax, nm, log ε): 226 (4.46), 283 (4.13), 294 (4.16), 329 (4.10).
PMR spectrum (300 MHz, DMSO-d , δ, ppm, J/Hz): 1.43 (6H, s, two CH -2), 2.02 (2H, m, CH -8), 2.64 (2H, m,
6
3
2
CH -9), 3.19 (2H, m, CH -7), 3.83 (3H, s, CH O-10), 5.69 (1H, d, J = 9.6, H-3), 6.34 (1H, s, H-11), 6.65 (1H, d, J = 9.6, H-4).
2
2
3
7
-Methoxy-2,2-dimethyl-chroman-5-ol (20) was prepared analogously to 13 from 16 (3.09 g, 14 mmol), zinc dust
(
9.0 g, 140 mmol), and conc. HCl (40 mL). Yield 93% as a light-yellow oil that was used for further transformations.
Tetrahydrocyclopenta[c]pyrano[2,3-h]chromen-6-ones 21 and 22. A solution of 20 (2.70 g, 13 mmol) and ethyl-
2
-oxocyclopentanecarboxylate (1.9 mL, 13 mmol) in ethanol (10 mL) was stirred vigorously and treated dropwise with conc.
H SO (20 mL). The resulting mixture was held at 50°C for 4 h, left overnight at room temperature, and poured into icewater
2
4
(
100 mL). The resulting solid was dissolved in CHCl (50 mL) and treated with NaOH solution (1 N, 2×50 mL) and saturated
3
NaCl solution. The organic layer was dried over anhydrous MgSO . The solvent was removed in vacuum in a rotary
4
evaporator. The oily product was crystallized from CH OH to give 21. The combined extracts of the alkaline solution were
3
acidified to pH 4. The resulting solid (22) was filtered off and crystallized from propan-2-ol.
1
0-Methoxy-2,2-dimethyl-3,4,8,9-tetrahydrocyclopenta[c]pyrano[2,3-h]chromen-6-one (21). Yield41%, mp191-
-1
1
1
92°C, empirical formula C H O . IR spectrum (KBr, cm ): 1724, 1622. 1602, 1486, 1470, 1436, 1378, 1326, 1208, 1152,
18 20 4
122, 1082. UV spectrum (EtOH, λmax, nm, log ε): 209 (4.51), 264 (3.91), 333 (4.12).
PMR spectrum (300 MHz, DMSO-d , δ, ppm, J/Hz): 1.32 (6H, s, two CH -2), 1.83 (2H, t, J = 7.2, CH -3), 2.04 (2H,
6
3
2
m, CH -8), 2.54 (2H, t, J = 7.2, CH -4), 2.71 (2H, m, CH -9), 3.21 (2H, m, CH -7), 3.79 (1H, s, CH O-10), 6.25 (1H, s, H-11).
2
2
2
2
3
1
0-Hydroxy-2,2-dimethyl-3,4,8,9-tetrahydrocyclopenta[c]pyrano[2,3-h]chromen-6-one (22). Yield38%, mp224-
-1
2
25°C, empirical formula C H O . IR spectrum (KBr, cm ): 3236, 2972, 1704, 1668, 1612, 1572, 1440, 1406, 1368, 1282,
17 18 4
1
256, 1160, 1120, 1064. UV spectrum (CH CN, λmax, nm, log ε): 212 (4.53), 324 (4.12).
3
PMR spectrum (300 MHz, DMSO-d , δ, ppm, J/Hz): 1.32 (6H, s, two CH -2), 1.76 (2H, t, J = 7.2, CH -3), 2.01 (2H,
6
3
2
m, CH -8), 2.54 (2H, t, J = 7.2, CH -4), 2.61 (2H, m, CH -9), 3.22 (2H, m, CH -7), 6.30 (1H, s, H-11), 10.21 (1H, s, OH-10).
2
2
2
2
2
,2-Dimethyl-10-(2-oxopropoxy)-3,4,8,9-tetrahydrocyclopenta[c]pyrano[2,3-h]chromen-6-one (23). Ahot solution
of 22 (1.14 g, 4 mmol) in absolute acetone (20 mL) was treated with freshly calcined potash (1.66 g, 10 mmol), vigorously
stirred, heated to 50-56°C, treated with chloroacetone (0.35 mL, 4.4 mmol), and held for 3 h with heating and vigorous stirring
(course of reaction monitored by TLC). After the reaction was complete, the mixture was cooled to room temperature, poured
into icewater (100 mL), and acidified to pH 4. The solid was filtered off and crystallized from propan-2-ol (75%). Yield 86%,
-1
mp 190-191°C, empirical formula C H O . IR spectrum (KBr, cm ): 1720, 1614, 1438, 1396, 1160, 1122, 1054.
2
0 22 5
UV spectrum (CH CN, λmax, nm, log ε): 214 (4.64), 322 (4.24).
3
PMR spectrum (300 MHz, DMSO-d , δ, ppm, J/Hz): 1.34 (6H, s, two CH -2), 1.80 (2H, t, J = 6.6, CH -3), 2.05 (2H,
6
3
2
m, CH -8), 2.19 (3H, s, CH -3′), 2.65 (2H, m, CH -4, CH -7), 3.26 (2H, m, CH -9), 4.85 (3H, s, CH -1′), 6.44 (1H, s, H-11).
2
3
2
2
2
2
431