Crystal and Molecular Structure of 7-Diethylamino-[1′,3′,3′-trimethyl-4-((1,3,3-trimethyl-1,3-dihydro-2H-indole-2-ylidene)methyl)-1′,3,3′,4-tetrahydrospiro[chromene-2,2′-indole]]: A Dicondensation Product From the Reaction of 4-Diethylaminosalicylaldehyde with Fischer's Base

The novel molecule, 7-diethylamino-[1′,3′,3′-trimethyl-4-((1,3,3-trimethyl-1,3-dihydro-2H-indole-2-ylidene)methyl)-1′,3,3′,4-tetrahydrospiro[chromene-2,2′-indole]], was isolated as the product from the condensation of diethylaminosalicylaldehyde with two equivalents of Fischer’s base and its crystal structure determined, initially using MoKα radiation. The diffraction data at higher theta angles (d < 0.9 Å) was notably weak so a further dataset was collected using CuKα to determine the cause. Although a different crystal batch and larger crystal was used and a better dataset obtained (with significantly improved atomic resolution) the comparison shows that the essential molecular features and weak intermolecular binding are duplicated in the refinement with the latter data. Comparison is made with a closely related structure. Consistent with observations for this related structure it is proposed that the product is formed through the interception of an intermediate carbinol by Fischer’s base.