Toward a symphony of reactivity: Cascades involving catalysis and sigmatropic rearrangements

Abstract

Catalysis and synthesis are intimately linked in modern organic chemistry. The synthesis of complex molecules is an ever evolving area of science. In many regards, the inherent beauty associated with a synthetic sequence can be linked to a certain combination of the creativity with which a sequence is designed and the overall efficiency with which the ultimate process is performed. In synthesis, as in other endeavors, beauty is very much in the eyes of the beholder. It is with this in mind that we will attempt to review an area of synthesis that has fascinated us and that we find extraordinarily beautiful, namely the combination of catalysis and sigmatropic rearrangements in consecutive and cascade sequences. Sometimes the assessment of beauty is nearly unanimous. The first four notes of Beethoven's 5th Symphony (Symphony No.5 in C minor, Op.67) represent perhaps the most well-known and popular motif in classical music. The orchestral score is shown in the background of the cover graphic. Accessed March 20, 2013 from http://imslp.org/wiki/Symphony-No.5,-Op. 67-%28Beethoven,-Ludwig-van%29. Unfinished Symphonies: The development of tandem processes has had a profound impact on organic synthesis. In this Review, catalyzed cascade transformations that involve sigmatropic rearrangements are discussed. To appeal to the musical sense of orchestration in chemical synthesis, we propose the descriptors duet, trio, quartet, etc. for defining transformations that involve more than one reaction in a cascade. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.