2,4,6-trialkylphenyl-2H-phospholes from slightly aromatic 1H-phospholes and their use in [4 + 2] cycloaddition reactions

1-(2,4,6-Trialkylphenyl)phospholes 1a,b possess a moderate aromatic character. Despite of that they underwent a sigmatropic rearrangement at 150°C to afford 2H-phospholes 2a,b which by trapping with tolane, or in reaction with another unit of 2 gave [4 + 2] cycloadducts 3a,b, or in a reversible reaction, dimer 6, respectively. Dedimerization of species 6 at 150°C in the presence of tolane, or at 0°C under oxidative circumstances, led to 1-phosphanorbornadiene 3a, or phosphole oxide dimer 8, respectively. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:316–319, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10151