N-(2-oxopropyl)acetamide → 1-(Acetamidomethyl)-1-methyl-1,3,4,9-tetrahydropyrano[3,4-b]indole

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Reaction Steps

A mixture of tryptophol (3.86 g; II, R2, R3, R4, R5, R6 = H and X1 =OH) and acetamidoacetone (3.0 g), see R. H. Wileg and O. H. Borum, J. Amer. Chem. Soc., 70, 2005 (1948), in 300 ml of dry benzene is stirred and heated to reflux. Water is collected in a Dean-Stark trap. After removal of the water five drops of boron trifluoride-etherate is added and the mixture refluxed 30 min. using the water-separator again. After stirring at room temperature overnight, the reaction mixture is evaporated to dryness. The solid residue is dissolved in chloroform and washed successively with 10% aqueous sodium bicarbonate, water, and brine. The chloroform solution is dried over magnesium sulfate, filtered, and evaporated. The residue is crystallized from benzene to yield 1-(acetamidomethyl)-1-methyl-1,3,4,9-tetrahydropyrano[3,4-b]indole, m.p. 100° - 102° C. This product is dried under reduced pressure at 27° C. Spectroscopic and analytical data show that the compound is solvated with one mole of benzene which can be removed completely only be melting. Rf values of the amide and tryptophol are equal.

Provenance & Evidence