title: One-Pot Coupling-Coupling-Cyclocondensation Synthesis of Fluorescent Pyrazoles.
abstract: Consecutive four-component coupling-coupling-cyclocondensation syntheses of pyrazoles and pyrimidines were developed by taking advantage of the provisional, sequentially Pd-catalyzed one-pot generation of alkynones from aryl iodides, ethynylmagnesium bromide, and acid chlorides. This one-pot methodology allows the concise, diversity-oriented generation of a set of donor-, acceptor-, and donor-acceptor-substituted pyrazoles, which are interesting fluorophores. Most distinctly, donor-acceptor pyrazoles display remarkably red-shifted emission maxima and pronounced positive solvochromicity, spanning an overall range from 363 nm (cyclohexane) to 595 nm (acetonitrile). DFT and TD-DFT calculations elucidate the electronic structure and the photophysical behavior. Upon photonic excitation, considerable charge-transfer character becomes apparent, which rationalizes the origin of huge Stokes shifts and solvochromic behavior.
authors.affiliation: Institut für Organische Chemie und Makromolekulare Chemie, Heinrich-Heine-Universität Düsseldorf , Universitätsstraße 1, D-40225 Düsseldorf, Germany.
authors.forename: Alissa C
authors.initials: AC
authors.lastname: Götzinger
authors.affiliation: Institut für Organische Chemie und Makromolekulare Chemie, Heinrich-Heine-Universität Düsseldorf , Universitätsstraße 1, D-40225 Düsseldorf, Germany.
authors.forename: Florian A
authors.initials: FA
authors.lastname: Theßeling
authors.affiliation: Institut für Organische Chemie und Makromolekulare Chemie, Heinrich-Heine-Universität Düsseldorf , Universitätsstraße 1, D-40225 Düsseldorf, Germany.
authors.forename: Corinna
authors.initials: C
authors.lastname: Hoppe
authors.affiliation: Institut für Organische Chemie und Makromolekulare Chemie, Heinrich-Heine-Universität Düsseldorf , Universitätsstraße 1, D-40225 Düsseldorf, Germany.
authors.forename: Thomas J J
authors.initials: TJ
authors.lastname: Müller