Abstract
Sequential transformations enable the facile synthesis of complex target molecules
from simple building blocks in a single preparative step. As part of a program concerned
with new methods for alkaloid synthesis, we have been utilizing a linked Pummerer/N-acyliminium
ion cyclization sequence because this combination offers unique opportunities for
the assemblage of complex target molecules. Cyclic 2-methylthio-5-amidofurans possessing
tethered π-bonds were prepared from various amido dithioacetals. Upon heating, these
systems undergo an intramolecular 4+2-cycloaddition reaction. The initially formed
Diels-Alder cycloadduct further rearranges by ring opening of the oxygen bridge followed
by a subsequent 1,2-methylthio shift. The method has been successfully applied to
several different families of alkaloids.
Key words
Pummerer reaction - Mannich reaction - Diels-Alder reaction - cyclization -
N -acylium ions
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