(Hive Addict)
05-23-03 09:27
No 434913
(Rated as: excellent)
As req'd by a certain Bee...
Total synthesis of mimosamycin
H Fukumi, H Kurihara, H Mishima. Chem Pharm Bull 26(7) (1978) 2175-2180.
[...]
3-methoxy-4-methylbenzaldehyde - 4-methyl-3-nitrobenzaldehyde (110 g) was added at once to a solution of SnCl2.2H2O (450 g) in 35% HCl (600 mL). The reaction was highly exothermic. As soon as the inner temperature of the reaction mixture reached at 100°C, the mixture was cooled to 0-5°C with ice-cooling. The resulting precipitates (stannic complex of 3-amino-4-methylbenzaldehyde) were filtered off and used to the following diazotization reaction without purification. To the suspended mixture of the complex in 35% HCl (600 mL) was added dropwise at 4-5°C a solution of NaNO2 (46 g) in H2O (50 mL) for 50 min. The mixture was stirred at the same temperature for 2 h, and the resulting pale yellow precipitates were filtered off. A solid of the dizaonium salt was added in portions to refluxing water (1.71) over 30 min and after evolution of nitrogen gas ceased, the mixture was cooled and extracted with DCM. Concentration of DCM extracts gave a crude product, which was purified by DCM elution through a short silica gel layer and by recystallization from benzene. Yield of 3-hydroxy-4-methylbenzaldehyde [1] was 54.5 g (60%). To a solution of 3-hydroxy-4-methylbenzaldehyde (10.6 g) in 2 N NaOH (60 mL) was added dropwise at 40-45°C Me2SO4 (15.9 g) for 10 min. The mixture was stirred at the same temperature for 1 h, cooled to 20°C and extracted with ether (150 mL). Usual work-up and recrystallization from n-hexane gave colorless needles (8.6 g, 88.5%) of 3-methoxy-4-methylbenzaldehyde, which melted at 45-46°C (lit [2] bp 101-103°C/10^-4 mmHg).
[1] NV Sidgwick e.a. JCS 123 (1923) 2819
[2] K Tsuda e.a. Chem Pharm Bull 10 (1962) 856.
The faster you run, the quicker you die.
(Chief Bee)
07-27-03 08:00
No 450087
(Rated as: excellent)
Baker's yeast-mediated enantioselective synthesis of the bisabolane sesquiterpenes
Claudio Fuganti and Stefano Serra
J. Chem. Soc., Perkin Trans. 1, 2000, (22), 3758 - 3764
DOI:10.1039/b006141g (free PDF!)
From the text:
However, 3-methoxy-4-methylacetophenone 14 was prepared using a completely different approach. Since the reported procedure based on a functionalization of p-methylacetophenone17 afforded 14 in only low yield, we decided to construct the aromatic ring by benzanullation18 of the hexadienoic acid derivative 12. This latter was prepared from crotonaldehyde 10 by Wittig reaction with ylide 1119, and then was submitted to cyclization using ethyl chloroformate and triethylamine as base. After KOH treatment, we obtained the acid 13, which was converted into the suitable acetophenone 14 in good yield by a number of straightforward synthetic steps.
The idea here is to stop their synthesis at the aldehyde stage, before they react it with the grignard reagent to form the phenylethanol. Thus the synthesis of would look like this:
(E,E )-3-(Ethoxycarbonyl)hepta-3,5-dienoic acid 12
Crotonaldehyde 10 (18 g, 257 mmol) as a solution in benzene (150 mL) was treated with 1-ethyl hydrogen 2-(triphenylphosphanylidene) butane-1,4-dioate 11 (100 g, 246 mmol) at reflux for 4 h. The solvent was removed under reduced pressure, the residue was dissolved in hexane–diethyl ether (2:1), and the triphenylphosphine oxide eliminated by crystallization. The liquid phase was concentrated and the remaining oil was purified by chromatography using hexane–ethyl acetate (gradient from 95:5 to 8:2) as eluent to afford exclusively the acid 12 (36g, 74%) as a single (E,E) isomer, mp 72–73°C (from hexane).
3-Hydroxy-4-methylbenzoic acid 13
ClCO2Et (21 mL, 220 mmol) was added in one portion to a solution of acid 12 (35 g, 177 mmol) in dry THF (200 mL), and then Et3N (75 mL, 538 mmol) was added dropwise, keeping the temperature under 20°C. The mixture was stirred for 15 min and then acidified with an excess of 5% aq. HCl and extracted with ethyl acetate (3×150 mL). The organic phase was concentrated and the residue was dissolved in ethanol (80 mL). The resulting solution was treated with aq. KOH (25 g, 445 mmol in 100 mL) and heated at reflux for 2 h. After cooling, the mixture was acidified with conc. HCl and extracted with ethyl acetate (3×150 mL). The combined organic portions were washed with brine (100 mL), dried (Na2SO4), and concentrated under reduced pressure. The residue was purified by chromatography using hexane–ethyl acetate (using a gradient from 8:2 to 1:2) as eluent followed by crystallization to give pure acid 1326 (23.2 g, 86%), mp 220–221°C (from hexane–ethyl acetate).
3-Methoxy-4-methylbenzaldehyde
Acid 13 (20 g, 132 mmol) as a solution in dry acetone (200 mL) was refluxed for 10 h with Me2SO4 (38 mL, 402 mmol) and dry K2CO3 (65 g, 470 mmol). The resulting mixture was concentrated under reduced pressure, diluted with water (300 mL) and extracted with diethyl ether (3×150 mL). The organic phase was dried (Na2SO4), concentrated under reduced pressure, and the residue was reduced at rt with LiAlH4 (6 g, 158 mmol) in dry THF (150 mL). The reaction was quenched by dropwise addition of ethyl acetate (200 mL) followed by addition of 5% aq. HCl (200 mL). The organic phase was separated, and the aqueous layer was extracted with diethyl ether (3×150 mL). The combined organic phases were washed with brine (200 mL), dried (Na2SO4), and concentrated under reduced pressure. The obtained benzylic alcohol was dissolved in CHCl3 (200 mL) and treated with MnO2 (50 g, 575 mmol) at reflux for 3 h. The reaction mixture was filtered and the liquid phase was concentrated under reduced pressure.
References:
[17] A. R. Pinder, S. J. Price and R. M. Rice, J. Org. Chem., 37, 2202 (1972)
[18] E. Brenna, C. Fuganti, V. Perozzo and S. Serra, Tetrahedron, 53, 15029 (1997)
[19] R. F. Hudson and P. A. Chopard, Helv. Chim. Acta, 46, 2178 (1963)
[26] J. J. Brown and G. T. Newbold, J. Chem. Soc., 1285 (1953)