Expecting the unexpected – a personal retrospective outlook on unusual reactions, including rearrangements

The review provides a retrospective outlook on the research of Israel Agranat, the author, in Organic Chemistry, commenced three score and seven years ago. Many of his research projects resulted unexpectedly in unusual reactions, not according to plans/objectives. The author’s M.Sc. and Ph.D. works were carried out at The Hebrew University of Jerusalem under the supervision of the author’s Doktorvater Professor Ernst David Bergmann (1903–1975), who had a profound effect on the author’s scientific thinking. The inevitable conclusion is that unexpected results were not exceptions but a light motif. In many instances, the unexpected results were missing the targets. An example is the failed attempted synthesis of 5H-dibenzo[b,f]azepine (1), an entry to the antidepressant imipramine (2). However, in certain cases, the unexpected results were a blessing, which had an impact on the author’ scientific career. A case in point is the serendipitous discovery of the reversibility of Friedel–Crafts acylations referred to as the Agranat-Gore rearrangement. The discovery of the novel aromatic tris(3-guaiazulenyl)cyclopropenium cation 117, with the highest pK_R+ > 10 value, due to stabilization of a nonbenzenoid aromatic by nonbenzenoid aromatics, was later surprisingly named ‘Agranat’s cation’, leading with tris(7H-dibenzo[c,g]fluorenylidenemethyl)methide anion 120 to the genuine hydrocarbon salt [Agranat’s cation⁺ – Kuhn’s anion^–] 119. Following Sir Isaiah Berlin’s theme in “The Hedgehog and the Fox”, the author considers himself a fox, rather than a hedgehog. Foxes are more prone than hedgehogs to pursue unexpected results. The present collection of unexpected unusual reactions and rearrangements raises the question of expecting the unexpected.