2-(1-Methyl-1H-indol-3-ylmethylene)-1-aza-bicyclo[2.2.2] octan-3-one: Acid-catalyzed isomerization of the Z isomer to the E isomer

Crystals of (Z)-2-(1-methyl-1H-indol-3-ylmethylene)-1-aza-bicyclo[2.2.2] octan-3-one (I) were obtained from a condensation reaction of 1-methyl-1H-indole-3-carboxaldehyde with 1-aza-bicyclo[2.2.2]octan-3-one and subsequent crystallization of the product from methanol. The isomeric (E)-2-(1-methyl-1H-indol-3-ylmethylene)-1-aza-bicyclo[2.2.2] octan-3-one hydrochloride (II) was obtained by treating a methanolic solution of I with a 1M solution of hydrogen chloride diethyl ether, followed by crystallization of resultant product from methanol. Crystal data: I, is monoclinic, P2₁, a = 5.7440(10), b = 11.102(2), c = 10.708(2) Å, β = 91.751(10)°, and V = 682.5(2) ų with Z = 2, for D_cal = 1.296 mg/m³ and II, is monoclinic, P2₁/c, a = 8.8510(2), b = 17.4990(5), c = 20.4300(5) Å, β = 101.3620(12)°, V = 3102.26(14) with Z = 8, for D_cal = 1.316 mg/m³.