Note from the Editor:
August KekulĂ©'s dream and his theory of the structure of benzene (1865). Julius Thomsen's logic that benzene contains equivalent electrons between its carbon atoms (ca. 1900). Richard WillstĂ€tter's synthesis and observation that 1,3,5,7âcyclooctatetraene is not aromatic (early 1900s). Sir Robert Robinson's proposal of the âaromatic sextetâ (1925). Erich HĂŒckel's molecular orbital treatment of benzene and other unsaturated compounds that separated sigma and pi electrons (early 1930s). Tetsuo Nozoe and Michael Dewar's independent proposal of a new aromatic structure for a cycloheptatrieneone (midâ1940s). Ronald Breslow's demonstration that cyclopropenyl cation is aromatic (1958). Breslow's proposal of âantiaromaticityâ (1965). I offer several comments. First, in the field of aromaticity, Breslow is in mighty exceptional company. Second, his research has extended well beyond aromaticity. Yes, Breslow is applying the concepts of antiaromaticity toward the development of highly conductive organic materials. But his research has encompassed enzyme mimics, remote functionalization reactions, unnatural DNA analogues and cancer chemotherapy. Indeed, Breslow is the coâdiscoverer of a highly successful drug, Vorinostat, which is FDAâapproved for the treatment of cutaneous Tâcell lymphoma. We thank Professor Breslow for joining our project honoring his and our friend, Tetsuo Nozoe. Tetsuo Nozoe would have would have been deeply touched.
âJeffrey I. Seeman
Guest Editor
University of Richmond
Richmond, Virginia 23173, USA
Eâmail: jseeman@richmond.edu
Ronald Breslow with Koji Nakanishi (left) and Tetsuo Nozoe (center), Sendai, 1970.
Abstract
We contributed to the field of nonâbenzenoid aromatic compounds by creating the cyclopropenyl cation and various of its derivatives, including cyclopropenone; it was the first aromatic system with other than six pi electrons in a single ring, and the simplest aromatic system. The pioneering work of Tetsuo Nozoe in tropolone chemistry was celebrated with the founding of ISNA, the International Symposium on NonâBenzenoid Aromatic Compounds, where I described our work in the field. It fit the prediction that aromaticity would be found in systems with 4nâ+â2 pi electrons, where n is an integer. I was also concerned with the properties of monocyclic systems with 4n cyclically conjugated pi electrons. They were expected not to be aromatic, but the interesting question was whether they were actually antiaromatic, especially destabilized by the cyclic conjugation in such 4n species as the cyclopropenyl anion, cyclobutadiene, and cyclopentadienyl cation. The evidence supports antiaromaticity in these cases. We also examined compounds where 4n cyclic pi systems were fused with aromatic systems, and most interestingly systems in which two 4n pi systems were fused. In these cases the periphery of the molecules had 4nâ+â2 pi electrons, for aromaticity, but the components were antiaromatic. Recently we have studied electrical conductivities in aromatic molecules such as thiophe...