A Novel Two-Carbon Homologation with N-Vinylacetamides and Ethyl Vinyl Ether as Acetaldehyde Anion Equivalents in the Synthesis of 9H-Xanthene, 9H-Thioxanthene, and 9,10-Dihydro-9-acridine Carboxaldehydes

An efficient synthesis of 9H-xanthene-9-carboxaldehyde (3a), 9H-thioxanthene-9-carboxaldehyde (3b), and 9,10-dihydro-10-methyl-9-acridinecarboxaldehyde (3c) by a novel two-carbon homologation of xanthydrol (1a), thioxanthydrol (1b), and 9,10-dihydro-10-methyl-9-acridinol (1c), respectively, using N-vinylacetamides (2a,b) or ethyl vinyl ether (2c) as acetaldehyde anion equivalents, is described.