A Concise Synthesis of (+)-Sporochnol A
4007
eluent to furnish aldehyde 2. Yield: 52.1% (9.38 g). IR (film): 1722, 1452,
1
1378, 1004, 917 cm21; H NMR (CDCl3): d 1.15 (s, 3H), 1.40 (t, 2H), 1.59
(s, 3H), 1.66 (s, 3H), 1.90 (m, 2H), 2.36 (d, 2H), 5.08 (t, 1H), 5.86–4.96
(m, 3H), 9.70 (t, 1H); 13C NMR (CDCl3): 202.5, 144.7, 131.1, 123.8, 112.7,
52.6, 41.0, 38.6, 25.3, 22.3, 17.2 ppm; MS (m/e): 180 (Mþ).
Preparation of 4-(1,5-dimethyl-1-ethenyl-4-hexene)cyclohex-2-enone
(4). To an ice-cooled mixture of piperidine (7.5 g, 0.1 mol) and anhydrous
K2CO3 was added dropwise aldehyde 2 (9 g, 0.05 mol). After stirring an
additional 2 h the solution was filtered, then the residue washed with anhy-
drous ether and added to the original filtrate. The excess piperidine was
removed under reduced pressure. Freshly distilled methyl vinyl ketone was
added to the above residue in nitrogen atmosphere. After stirring for 24 h at
room temperature under a nitrogen atmosphere, the mixture was refluxed
with 4 mL glacial acetic acid for 4 h, then it was diluted with water and iso-
lated by ether extraction. The organic layer was dried and the solvent
removed. The crude oil was chromatographed on silica gel with hexane-
ether (20 : 1) as eluent to give the a,b-unsaturated ketone 4. Yield: 67.2%
1
(7.79 g). IR (film): 1687, 1620, 1450, 1380, 1141, 1002, 916, 835 cm21; H
NMR (CDCl3):d 0.96 (d, 3H), 1.33 (t, 2H), 1.51 (s, 3H), 1.60 (s, 3H), 1.80
(m, 2H), 2.06 (m, 2H), 2.26 (m, 2H), 2.43 (m, 1H), 5.67–4.90 (m, 3H),
5.14 (t, 1H), 5.94 (dd, 1H), 6.88 (tt, 1H); 13C NMR (CDCl3): 199.8, 153.1,
144.6, 131.5, 129.9, 124.2, 114.2, 44.2, 44.8, 38.7, 37.7, 25.5, 23.8 ppm;
MS (m/e): 232 (Mþ).
Preparation of a,b-unsaturated aldehyde (3). A solution of 9 g
(0.05 mol) of the aldehyde 2 and 7.5 g (0.1 mol) of 40% HCHO aq in 50 mL
of ethanol containing 0.5 mL of piperidine and 0.5 mL of acetic acid was
refluxed for 2 h. The ethanol was removed under reduced pressure. The
residue was chromatographed on silica gel with acetone-petroleum ether
(1 : 50) to obtain compound 3. Yield: 94.3% (9.1 g). IR (film): 1698, 1452,
1
1373, 1008, 917, 873 cm21; H NMR (CDCl3): d 1.25 (s, 3H), 1.52 (s, 3H),
1.60 (s, 3H), 1.82-1.57 (m, 4H), 5.05 (t, 1H), 5.99–4.93 (m, 3H), 6.01
(s, 1H), 6.25 (s, 1H), 9.51 (s, 1H); 13C NMR (CDCl3): 194.1, 154.8, 144.2,
134.6, 131.3, 124.2, 112.6, 43.0, 37.8, 25.5, 23.1, 22.6, 17.5 ppm; MS
(m/e):192 (Mþ).
Preparation of 4-(1,5-dimethyl-1-ethenyl-4-hexene)cyclohex-2-enone
(4). The a,b-unsaturated aldehyde 3 (7.7 g, 0.04 mol), ethylacetoacetate
(6.5 g, 0.05 mol), EtONa (2.18 g, 0.032 mol) and ethanol (150 mL) were
refluxed in a 250 mL round-bottom flask for 6 h. Upon cooling to room temp-
erature, the mixture was quenched with 1 M HCl solution, diluted with a 1 : 1
mixture of ether and benzene, washed with 1 M NaOH solution and brine. The
separated organic layer was dried over anhydrous Na2SO4, filtered, and con-
centrated under reduced pressure. The crude product was chromatographed