Reagents:
- Indole (cas 120-72-9) 25.0 g, 211 mmol;
- Diethyl ether 700 mL;
- Oxalyl chloride (cas 79-37-8) 55.0 g, 433 mmol;
- Dimethylamine 1.94 mol in diethyl ether 20% wt/vol solution;
- Distilled water 1 l;
- LAH 1 M solution in THF 800 mL, 800 mmol;
- Sulfuric acid (H2SO4 100%) 21.3 mL, 400 mmol;
- THF anhydrous ~400 mL;
- Glauber's salt (Na2SO4[H2O]10) 90 g, 279 mmol;
- Heptane 250 mL;
Equipment and glassware:
- Round bottom flasks 3 L and 5 L;
- Top stirrer;
- Ice water bath;
- Pressure-equalized addition funnel;
- pH indicator papers;
- Filter paper;
- Buchner flask and funnel;
- Vacuum desiccator (optional);
- Temperature probe or thermometer;
- Friedrich condenser;
- Heating mantle;
- Celite 545;
- Beakers 1L, 500 ml x2, 250 ml x2; 100 ml x2;
- Glass rod and spatula;
2-(1H-Indol-3-yl)-N,N-dimethyl-2-oxoacetamide
Indole (25.0 g, 211 mmol) was dissolved in 400 mL diethyl ether, maintained at 0 °C, in a 3 L round bottom flask equipped with an overhead stirrer and ice bath. A 0 °C solution of oxalyl chloride (55.0 g, 433 mmol) in 100 mL diethyl ether was prepared and added in a rapid stream over a 30 sec period to the stirred indole solution via a pressure-equalized addition funnel. During the addition, yellow crystalline 1H-indol-3-yl(oxo)acetyl chloride precipitated immediately. Stirring was continued for 30 min after the oxalyl chloride addition was complete. The yellow 1H-indol-3-yl(oxo)acetyl chloride was not isolated, but the ethereal suspension was used directly in the next step.
A 20% wt/vol solution of dimethylamine in diethyl ether, prepared at 0 °C, was added dropwise to the vigorously stirred ethereal suspension of the 1H-indol-3-yl(oxo)acetyl chloride until the pH reached 9-10 (9.2 molar equivalents of dimethylamine:starting indole were added), while maintaining the reaction at 0 °C with the ice bath. After the addition was complete, an ivory-colored slurry of the 2-(1H-indol-3-yl)-N,N-dimethyl-2-oxoacetamide was observed within the reaction flask. Stirring was continued for 60 min, then the flask contents were suction-filtered through a Whatman #2 filter paper using a Büchner funnel. The filter cake was washed with 200 mL fresh diethyl ether and suctioned dry. This product was washed twice as follows: the filter cake was slurried in 500 mL water, stirred for 5 min, vacuum filtered using a Büchner funnel, resuspended in 500 mL fresh water, stirred for 10 min, then suction filtered once again. This near-white filter cake of 2-(1H-indol-3-yl)-N,N-dimethyl-2-oxoacetamide was suctioned dry, then placed in a vacuum drying oven at 40 °C or in a vacuum desiccator and dried to a constant weight. Yield 30.6 g (141 mmol, 67% of theory).
N,N-dimethyltryptamine (DMT)
2-(1H-Indol-3-yl)-N,N-dimethyl-2-oxoacetamide was reduced to DMT using a solution of aluminum hydride (AlH3; alane) in tetrahydrofuran (THF). Alane was generated in situ from lithium aluminum hydride (LAH). A 5 L round bottom reaction flask was equipped with a temperature probe, ice bath, Friedrich condenser, pressure-equalized dropping funnel, and overhead stirrer. To generate AlH3 in situ, a 1 M solution of LAH in dry THF (800 mL, 800 mmol) was charged to the reaction flask and stirred, until the solution reached a temperature of 2 °C. One hundred percent sulfuric acid (21.3 mL, 400 mmol), produced by treating 96% H2SO4 with oleum (24.7% SO3), was added to the cold LAH solution, dropwise with vigorous stirring to avoid charring, over a period of one hour. Hydrogen is evolved, and lithium sulfate precipitates to give a clear solution of AlH3 in THF. To this mixture, a solution of 2-(1H-indol-3-yl)-N,N-dimethyl-2-oxoacetamide (3, 19.2 g, 89 mmol) in 200 mL anhydrous THF was added rapidly with stirring, while maintaining the temperature in the range of 0-4 °C. After the addition was complete, the fluorescent yellow-green reaction was stirred for 30 min on ice, then the ice bath was removed and replaced with a heating mantle. The reaction was heated to reflux for 3 hr, then returned to the ice bath.
Glauber's salt (Na2SO4[H2O]10; 90 g, 279 mmol) was added in portions with vigorous stirring to quench the reaction, maintaining the temperature below 10 °C. The formed greyish-white solids were removed by filtration through Celite 545 using a Büchner funnel with Whatman #2 filter paper. The filter cake was washed twice with fresh THF, resuspending the filter cake for each wash to recover any entrained product. The transparent light yellow filtrate was concentrated by rotary evaporation to yield 23.0 g of a transparent orange-yellow oil. The oil was dissolved in 250 mL boiling heptane, then allowed to stand at 4 °C; free base N,N-dimethyltryptamine (cas 61-50-7) crystallized as pure white crystals. Yield 12.6 g (66.7 mmol, 75% of theory).
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