Domino reactions in the synthesis of heterocyclic natural products
L. F. Tietze and N. Rackelmann
Institut für Organische und Biomolekulare Chemie, Georg-August
Universität- Göttingen, 37077 Göttingen, Germany
Abstract: Domino reactions are defined as processes of two or
more bond-forming reactions under identical conditions, in which the
subsequent transformation takes place at the functionalities obtained
in the former transformation. They allow the efficient synthesis of
complex molecules from simple substrates in an ecologically and economically
favorable way. A very powerful domino process is the domino Knoevenagel–hetero-Diels–Alder
reaction, in which an aldehyde or an beta-ketoester is condensed with
a 1,3-dicarbonyl compound or a heteroanalog to give a 1-oxa-1,3-butadiene,
which can undergo an inter- or intramolecular hetero-Diels–Alder reaction
with dienophiles such as enol ethers or alkenes. The products are dihydropyrans,
which can be transformed in a variety of ways. Thus, an extension of
the process is the synthesis of highly substituted pyrrolidines, piperidines,
and azepanes using aminoaldehydes. The process has also been employed
for the enantioselective total synthesis of a variety of alkaloids,
such as indol- and ipecacuanha alkaloids. In another domino process,
erythrina and homoerythrina alkaloids have been prepared from simple
phenylethylamines and ketoesters.
* Plenary lecture presented at the 5th Florida Heterocyclic
Conference, Gainesville, FL, USA, 7-10 March 2004. Other presentations
are published in this issue, pp. 1933-1983.
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