Versatile pyrolytic synthesis of fused polycyclic heteroaromatic compounds

Thirty-six new stabilised phosphonium ylides designed to undergo thermal loss of Ph₃PO and radical domino cyclisation have been prepared and are generally found to undergo the desired reaction under flash vacuum pyrolysis conditions at 850 °C. A wide range of tetra- and penta-cyclic fused ring heterocycles, many previously unknown, are thus formed in moderate to high yield in a single step. By using suitably substituted starting materials, substituents such as CH₃ and Cl can be installed at various positions in the products. The method has also been demonstrated in a combinatorial mode to generate a small library of twelve fused ring heterocycles in a single pyrolysis.