C([N-][CH:5]([CH3:7])[CH3:6])(C)C.[Li+].CN1CCCN(C)[C:11]1=[O:17].[CH:18]1(N=C/C=C/C)[CH2:23][CH2:22][CH2:21][CH2:20]C1.Br[CH2:30]CC=C(C)C>O1CCCC1>[CH3:30][C:5]([CH3:6])=[CH:7][CH2:18][CH2:23][C:22](=[CH:21][CH3:20])[CH:11]=[O:17]
To a stirred solution of lithium diisopropyl amide (14.0 mmol) in 10 ml tetrahydrofuran (THF) at -10° under argon was added 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU) (1.7 ml, 14.0 mmol), followed after 45 minutes by the dropwise addition of crotonaldehyde cyclohexylimine (1.9 g, 12.7 mmol) in 2 ml THF. After 10 minutes at 0° the solution was cooled to -78° and stirred an additional 30 minutes, upon which time was added 1-bromo-4-methyl-3-pentene (2.49 g., 15.3 mmol) in 1 ml THF. After 4.5 hours at -70° to -65°, the reaction mixture was quenched with saturated ammonium chloride solution, warmed to room temperature, and extracted two times with ethyl ether. The organic portions were combined, washed four times with water, once with saturated sodium chloride, dried over magnesium sulfate and filtered. This ethyl ether solution was subsequently stirred for two hours at room temperature with 25 ml buffered acetic acid solution (pH 4.5). The organic portion was then washed twice with water, once with saturated sodium bicarbonate solution, once with sodium chloride solution, dried over magnesium sulfate, filtered and distilled at atmospheric pressure until about 25 ml of solution remained in the still pot. The residue was purified by flash chromatography (silica, 5 to 10% ethyl ether/hexane), the desired fractions were concentrated by distillation, and the residue was distilled (Kujelrohr, 25 mm 85° to 90°) to give the purified aldehyde as a pale yellow, volatile liquid.
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