Recent Uses of Kröhnke Methodology: A Short Survey

Abstract

The scope of this short review is to point out how such an old reaction as the Kröhnke-type ring closure is still used nowadays to enable simple access to pyridines or polypyridines. Besides the usual Stille or Suzuki coupling reactions, which deal, respectively, with stannylated derivatives or boronic derivatives, the Kröhnke reaction can reach its target molecules with commercially available starting materials in a simple reaction medium without any special care.

A Unified Approach to the Isomeric α-, β-, γ-, and δ-Carbolines via their 6,7,8,9-Tetrahydro Counterparts

“…The reaction sequences reported here should allow for the rational/logical design of pathways to a wide range of α-, β-, γ-, and δ-carbolines. This is all the more so given the increasingly ready availability of a wide range of polysubstituted pyridines and 2-iodocyclohex-2-en-1-ones. For similar reasons, the protocols defined here should allow for ready access to a wide range of azaindoles, compounds of considerable interest from a medicinal chemistry perspective .…”

4′-(5-Methylfuran-2-yl)-2,2′:6′,2″-terpyridine: A New Ligand Obtained from a Biomass-Derived Aldehyde with Potential Application in Metal-Catalyzed Reactions

“…Apart of providing terpyridines with interesting properties, the use of furfural in Many methods are available for the preparation of terpyridine derivatives [6][7][8]. A classical method, the so-called Kröhnke's method [9,10] involves the reaction of 2-acetylpyridine and an aldehyde. Biomass-derived aldehyde furfural has been already used for the preparation of terpyridines [11].…”

Synthesis and properties of fluorescent 4′-azulenyl-functionalized 2,2′:6′,2″-terpyridines

“…The target compounds have been prepared following the Kröhnke-type synthetic methodology [23–24] starting from azulene carbaldehydes ( 1 ) [25] and 2-acetylpyridine (Scheme 1). In the first step, the 1-azulenyl-2′-azachalcone precursor 2 is formed via a Claisen–Schmidt aldol condensation.…”