Heterocyclization of a Substituted Pyranone
1321
4-ꢀCyclohex-20-enyloxy)-6-methyl-2-one ꢀ3; C12H14O3)
A mixture of 1.26g 4-hydroxy-6-methylpyran-2-one ꢀ10 mmol), 1.6 g 3-bromocycloxene ꢀ10 mmol),
and 3 g anhydrous K2CO3 was re¯uxed in 100 cm3 dry acetone for 5 h. The reaction mixture was
cooled and ®ltered. The solvent was distilled off, and the residual mass was chromatographed over
silica gel. Elution of the column with benzene:ethyl acetate 9:1 gave compound 3 as a transparent
sticky liquid.
1
Yield: 1.1 g ꢀ55%); H NMR ꢀCDCl3, ꢀ, 300 MHz): 1.43±2.28 ꢀm, 6H), 2.21 ꢀs, 3H, C-6-CH3),
4.74±4.78 ꢀm, 1H, C1-H), 5.47 ꢀs, 1H, C3-H), 5.76 ꢀs, 1H, C5-H), 5.81±6.26 ꢀm, 2H, C2-H, C3-H) ppm;
IR ꢀKBr): ꢁ 1700, 1540, 1480, 1230 cmÀ 1; UV=Vis ꢀEtOH): ꢂmax 216, 277 nm; MS: m=z 206
ꢀM ).
3-ꢀCyclohex-20-enyl)-4-hydroxy-6-methylpyran-2-one ꢀ4)
A solution of 1 g ꢀ5 mmol) 3 in 3 cm3 xylene was re¯uxed for 17h. A solid was obtained after cooling
the reaction mixture; this was separated by ®ltration and puri®ed by recrystallization from an ace-
tone=petroleum ether mixture ꢀyield: 65%). The obtained compound was shown to be 4 by comparison
of its physical data with those of an authentic sample [8].
6-Methyl-90-iodo-20-oxabicyclo[3.3.1]nonano[3,2-c]pyran-2-one ꢀ6a; C12H13IO3)
A solution of 0.2 g ꢀ1mmol) 4 in 50cm3 dry CH3CN was stirred at 0±5ꢀC with 0.23 g ꢀ1mmol) solid
N-iodosuccinimide for 1 h. The solvent was distilled off, and the residual mass was dissolved in 50cm3
CHCl3. The organic phase was washed with 20cm3 saturated Na2SO3 solution, twice with 20 cm3 H2O,
and dried ꢀNa2SO4). Removal of CHCl3 gave a gummy residue which was puri®ed by column
chromatography over silica gel. Elution of the column with benzene:ethyl acetate 9:1 gave raw 6a
which was recrystallized from a CHCl3=petroleum ether mixture.
Yield: 0.25 g ꢀ80%); white solid; m.p.: 129±130ꢀC; 1H NMR ꢀCDCl3, ꢀ, 300MHz): 1.45±1.69 ꢀm,
Hg, Hi), 1.92±2.06 ꢀm, Hd, He, Hf), 2.10±2.20 ꢀm, Hh), 2.26 ꢀs, 3H, C6-CH3), 3.43±3.50 ꢀdt, J 6.8 and
6.7 Hz, Hc), 4.25±4.33 ꢀddd, J 10, 6.9, and 4.5 Hz, Ha), 5.05±5.10 ꢀdd, J 6.9 and 6.7 Hz, Hb), 5.97
ꢀs, 1H) ppm; IR ꢀKBr): ꢁ 1100, 1200, 1240, 1400, 1560, 1690 cmÀ 1; UV=Vis ꢀEtOH): ꢂmax 211,
297 nm; MS: m=z 332 ꢀM ).
6-Methyl-90-bromo-20-oxabicyclo[3.3.1]nonano[3,2-c]pyran-2-one ꢀ6b; C12H13BrO3)
A solution of 0.2 g ꢀ1mmol) 4 in 100 cm3 CHCl3 was stirred with 0.32g ꢀ1mmol) solid pyridinium
hydrotribromide [19] or 0.38g ꢀ1mmol) hexamine hydrotribromide [20] at 0±5ꢀC for 1 h or 40min,
respectively. The CHCl3 solution was washed twice with 10cm3 5% Na2CO3 solution, twice with
25cm3 H2O, and dried ꢀNa2SO4). Evaporation of CHCl3 left a gummy residue which was puri®ed by
column chromatography over silica gel. Compound 9 was obtained when the column was eluted with
benzene:ethyl-acetate 4:1. The material was then recrystallized from a CHCl3=petroleum ether
mixture.
1
Yield: 0.2 g ꢀ72%); white solid; m.p.: 88±89ꢀC; H NMR ꢀCDCl3, ꢀ, 500 MHz): 1.53±1.60 ꢀm,
Hg), 1.70±1.75 ꢀm, Hi), 1.87±1.94 ꢀm, He), 1.99±2.03 ꢀq, J 6.5 Hz, Hd, Hf), 2.14±2.20 ꢀm, Hh), 2.25
ꢀs, 3H, C6-CH3), 3.60±3.64 ꢀdt, J 6.6 and 6.4Hz, Hc), 4.26±4.30 ꢀddd, J 10, 6.7, and 4.5 Hz, Ha),
4.96±4.99 ꢀdd, J 6.7 and 6.4 Hz, Hb), 5.96 ꢀs, 1H) ppm; IR ꢀKBr): ꢁ 1110, 1270, 1430, 1580,
1670 cmÀ 1; UV=Vis ꢀEtOH): ꢂmax 211, 281 nm; MS: m=z 284, 286 ꢀM ).
6-Methyl-20-oxabicyclo[3.3.1]nonano[3,2-c]pyran-2-one ꢀ6c; C12H14O3)
Compound 4 ꢀ0.1g, 0.5 mmol) was added in portions to 2 cm3 concentrated H2SO4 at 0±5ꢀC, and the
mixture was stirred for 2 h at this temperature. The solution was then poured into crushed ice and