| 95.1% |
With sulfuric acid; hydrogen bromide; In water; at 100℃; for 16h; |
(1) Synthesis of 1-bromo-3,7-dimethyloctane 3,7-Dimethyloctan-1-ol (10.0 g, 63.2 mmol) was suspended in 48% aqueous hydrobromic acid solution, concentrated sulfuric acid (0.17 ml) was added dropwise and the mixture was stirred at 100 C. for 16 hr. The reaction mixture was allowed to cool to room temperature, extracted with hexane (200 ml), and washed twice with 5% aqueous sodium hydrogen carbonate solution (100 ml) and once with 20% brine (100 ml). The organic layer was dried over sodium sulfate, and the solvent in the filtrate was evaporated to give the title compound (13.3 g, 95.1%) as a colorless oil. |
| 82.1% |
With sulfuric acid; hydrogen bromide; |
(1) Synthesis of 3,7-dimethyl-1-octyl bromide 48% HBr (200 ml) and concentrated sulfuric acid (0.46 ml) were added to 3,7-dimethyl-1-octanol (21.0 g, 157.9 mmol), and the mixture was heated overnight. After allowing to cool to room temperature, and the mixture was extracted with hexane. The organic layer was washed with 5% aqueous sodium hydrogen carbonate solution and saturated brine, dried and concentrated to give the title compound (28.7 g, 82.1%). |
|
With phosphorus tribromide; In hexane; water; |
Preparation 17 To neat 3,7-dimethyloctanol (5 ml) was added phosphorus tribromide (1.01 ml). The mixture was stirred for 4 hours at 60 C. The reaction mixture was added to a mixture of water and n-hexane. The organic layer was separated and dried over magnesium sulfate. The magnesium sulfate was filtered off, and the filtrate was evaporated under reduced pressure to give 3,7-dimethyloctyl bromide (4.40 g). IR (Neat): 2900, 1450 cm-1 NMR (CDCl3, delta): 0.87 (6H, d, J=6.6 Hz), 0.89 (3H, d, J=6.4 Hz), 1.1-1.3 (6H, m), 1.5-1.9 (4H, m), 3.3-3.5 (2H, m) |
|
With sulfuric acid; hydrogen bromide; tetra(n-butyl)ammonium hydrogensulfate; In water; |
General procedure: The synthesis of pyridine-based calamitic esters 3a-e is given in Scheme 1. Firstly, 4-Bromophenol was alkylated with the corresponding n-alkyl bromide to give 4-alkoxybromobenzene 1a-e[29-32]. 3,7-Dimethyloctyl bromide in racemic and chiral form were prepared from commercially available 3,7-Dimethyl-1-octanol and (S)-(-)-b-citronellol. As described previously [33], (S)-(-)-b-citronellol was firstly reduced by catalytic hydrogenation (H2,Pd/C in MeOH) to obtain (S)-3,7-dimethyl-1-octanol. Then, both alcohols reacted with. conc. aqu. HBr/conc. H2SO4 using tetrabutylammoniumhydrogensulfate (TBAHS) as catalyst to obtain the corresponding 3,7-Dimethyloctyl bromides. Compounds 1a-e were subjected to halogen-lithium exchange reaction by using n-butyllithiumin 2.5M hexane solution, followed by the treatment with B(OCH3)3 and then acidic hydrolysis to obtain 4-alkoxybenzeneboronic acids 2a-e [29,31,34,35]. In the final step,compounds 2a-e reacted with commercially available Methyl 5-bromopyridine-2-carboxylate in 1,2-dimetoxyethane by using Pd(PPh3)4 as catalyst and saturated NaHCO3 solution to yield the target compounds 3a-e. |
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