Pyrrol-2-yl-trichloromethyl ketone

Pyrrole-2-carboxylic acid esters, from pyrrol-2-yl trichloromethyl ketone, 51, 102 PYRROLE—2-CARBOXYLIC ACID,... 

Pyrrolidinocyclohexene, preparation of, 54, 40 Pyrrol-2-yl-trichloromethyl ketone, with ethanol to give ethyl pyrrole-2-carboxylate, 51, 100... 

A. Pyrrol-2-yl trichloromethyl ketone. In a 3-1. three-necked round-bottomed flask equipped with a sealed mechanical stirrer, a dropping funnel, and an efficient reflux condenser with a calcium chloride drying tube are placed 225 g. (1.23 moles) of trichloroacetyl chloride and 200 ml. of anhydrous ether. The solution is stirred while 77 g. (1.15 moles) of freshly distilled pyrrole in 640 ml. of anhydrous ether is added over 3 hours (Note 1). The heat of reaction causes the mixture to reflux during the addition. Following the addition, the mixture is stirred for 1 hour, and then 100 g. (0.72 mole) of potassium... 

Methods of acylating pyrrole similar to the present one have been reported using oxalyl chloride,5 trifluoroacetic anhydride,6 carbamic acid chloride,7 and trichloroacetyl chloride.8 In the last preparation, it was necessary to separate the product from highly colored by-products by alumina chromatography. Pyrrol-2-yl trichloromethyl ketone has also been prepared by the interaction of pyrrolylmagnesium halide and trichloroacetyl chloride.9... 

B. Ethyl pyrrole-2-carboxylate. In a 1-1. three-necked round-bottomed flask equipped with a sealed mechanical stirrer and powder funnel are place 1.0 g. of sodium and 300 ml. of anhydrous ethanol. When the sodium is dissolved, 75 g. (0.35 mole) of pyrrol-2-yl trichloromethyl ketone from Part A is added portionwise over a 10-minute period (Note 4). After the addition is complete, the solution is stirred 30 minutes, then concentrated to dryness using a rotary evaporator. The oily residue is partitioned between 200 ml. of ether and 25 ml. of 3 N hydrochloric acid. The ether layer is separated, and the aqueous layer is washed once with 100 ml. of ether. The ether solutions are combined, washed once with 25 ml. of saturated sodium bicarbonate solution, dried with magnesium sulfate, and concentrated by distillation. The residue is fractionated at reduced pressure to give 44.0-44.5 g. (91-92%) of ethyl pyrrole-2 carboxylate as a pale yellow oil, b.p. 125-128° (25 mm.) (Note 5). The yield based on pyrrole is 70-74%. Upon standing at room temperature the product crystallizes, m.p. 40-42°. 

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