An efficient three-step synthesis of cyclopenta[b]pyrans via 2-donor-substituted fischer ethenylcarbenechromium complexes.
A wide range of cyclopenta[b]pyrans 4 has been synthesized in a one-pot reaction by treatment of different 2-donorsubstituted ethenylcarbenechromium complexes 2 with alkynes in THF in moderate to excellent yields (41-90 % for 14 out of 25 examples). The starting materials 2 are readily available in good to excellent yields (76-99 % for 25 out of 36 examples) by Michael addition of amines, alcohols and thiols, respectively, to the corresponding alkynylcarbenechromium complexes 1. Due to their 10 pi-electrons in a cross-conjugated bicyclic system, cyclopenta[b]pyrans have been termed pseudoazulenes, as they indeed have similar UV/Vis-spectroscopic properties.
de Meijere
Armin
A
Institut für Organische und Biomolekulare Chemie der Georg-August-Universität Göttingen, Germany.
Schirmer
Heiko
H
Stein
Frank
F
Funke
Frank
F
Duetsch
Michael
M
Wu
Yao-Ting
YT
Noltemeyer
Mathias
M
Belgardt
Thomas
T
Knieriem
Burkhard
B