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.

Toward a Symphony of Reactivity: Cascades Involving Catalysis and Sigmatropic Rearrangements

Optically pure hinckdentine A was synthesized on a 300 mg scale via an asymmetric catalysis-based strategy. The key steps to the first asymmetric synthesis involved (i) enantioselective dearomative cyclization of an achiral N-acyl indole that allowed for the efficient construction of the key polycyclic indoline intermediate with a crucial tetrasubstituted stereogenic carbon center, (ii) Beckmann fragmentation-mediated ring expansion, (iii) rearrangement-based introduction of an anilinic nitrogen atom, (iv) regioselective tribromination, and (v) final closure of the cyclic amidine moiety.

Enantioselective Total Synthesis of (+)-Hinckdentine A via a Catalytic Dearomatization Approach

Reaction of Thioacids with Isocyanates and Isothiocyanates: A Convenient Amide Ligation Process

Bis hin zu einer Symphonie der Reaktivität: Kaskaden mit Katalysen und sigmatropen Umlagerungen

Bioinspired Collective Syntheses of Iboga-Type Indole Alkaloids

Buta-1,3-dienyl thiocyanic acid ester reacts with acryloyl chloride in presence of Lewis acid catalysts to produce directly the rearranged product of type 3bvia a combination of a Diels-Alder reaction with a [3,3] sigmatropic shift; the 1,4-substituted cyclohexene is easily transformed into the 2-azabicyclo[2.2.2]oct-5-ene derivative 6b, which has been used as precursor for the synthesis of the Ibogamin skeleton.

Lewis-acid catalysed tandem reaction Diels–Alder–[3,3] sigmatropic shift between buta-1,3-dienyl thiocyanic acid ester and acryloyl chloride: application in the synthesis of 2-azabicyclo[2.2.2]oct-5-ene derivatives

The elimination of thiocyanic acid from the stereoisomers of the hex-3-ene-2,5-diyl dithiocyanates, 4a, 4b, 6a and 6b, in the presence of a strong neutral base in an organic solvent, yields mixtures of the hex-2,4-dien-2-yl thiocyanates 9, 10 and 11via a preferentially syn process.

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Joseph Schoepfer

Papers

Lewis-acid catalysed tandem reaction Diels–Alder–[3,3] sigmatropic shift between buta-1,3-dienyl thiocyanic acid ester and acryloyl chloride: application in the synthesis of 2-azabicyclo[2.2.2]oct-5-ene derivatives

The Stereochemistry of the 1,4-Elimination of Thiocyanic Acid from Hex-3-ene-2,5-diyl Dithiocyanates

The Stereochemistry of the 1,4‐Elimination of Thiocyanic Acid from Hex‐ 3‐ene‐2,5‐diyl Dithiocyanates.