A chiral analog of the bicyclic guanidine TBD: synthesis, structure and Brønsted base catalysis.
Starting from (S)-β-phenylalanine, easily accessible by lipase-catalyzed kinetic resolution, a chiral triamine was assembled by a reductive amination and finally cyclized to form the title compound10. In the crystals of the guanidinium benzoate salt the six membered rings of10adopt conformations close to an envelope with the phenyl substituents in pseudo-axial positions. The unprotonated guanidine10catalyzes Diels-Alder reactions of anthrones and maleimides (25-30% ee). It also promotes as a strong Brønsted base the retro-aldol reaction of some cycloadducts with kinetic resolution of the enantiomers. In three cases, the retro-aldol products (48-83% ee) could be recrystallized to high enantiopurity (≥95% ee). The absolute configuration of several compounds is supported by anomalous X-ray diffraction and by chemical correlation.
Institute for Organic Chemistry and Chemical Biology, Goethe University Frankfurt, Max-von-Laue-Straße 7, D-60438 Frankfurt am Main, Germany.
Mariano
M
Goldberg
Institute for Organic Chemistry and Chemical Biology, Goethe University Frankfurt, Max-von-Laue-Straße 7, D-60438 Frankfurt am Main, Germany.
Denis
D
Sartakov
Institute for Organic Chemistry and Chemical Biology, Goethe University Frankfurt, Max-von-Laue-Straße 7, D-60438 Frankfurt am Main, Germany.
Jan W
JW
Bats
Institute for Inorganic and Analytical Chemistry, Goethe University Frankfurt, Max-von-Laue-Straße 7, D-60438 Frankfurt am Main, Germany.
Michael
M
Bolte
Institute for Organic Chemistry and Chemical Biology, Goethe University Frankfurt, Max-von-Laue-Straße 7, D-60438 Frankfurt am Main, Germany.
Michael W
MW
Göbel
absolute configuration; anthrone; cycloaddition; kinetic resolution; lipase