Synthesis of Substituted Phenanthrene by Iron(III)-Catalyzed Intramolecular Alkyne–Carbonyl Metathesis

Abstract

An efficient synthesis of functionalized phenanthrenes has been developed for the first time involving an iron(III)-catalyzed intramolecular coupling of 2'-alkynyl-biphenyl-2-carbaldehydes. A broad range of functionalized phenanthrene derivatives could be obtained in the present method in moderate to good yields with high chemo- and regioselectivity. This transformation can also be applied to the synthesis of an angularly fused tetracyclic compound. This method offers several advantages such as high selectivity, mild reaction conditions, and easy availability of starting materials.

Iron Catalysis in Organic Synthesis

“…1318 Substituents such as methoxy, fluoro, chloro, and ester groups were tolerated under these conditions. In addition, a ketone could also be employed as carbonyl component.…”

Iron-Catalyzed Carbonyl–Alkyne and Carbonyl–Olefin Metathesis Reactions

“…Consequently, the reaction does not follow the Chauvin mechanism, as the metal is not included in the cycle formed in the transition structure. In general, the reaction itself is better described as an economical catalytic alternative to the Wittig reaction [27]. Nevertheless, carbonyl-alkyne metathesis consists of formal [2 + 2] and retro [2 + 2] cycloadditions and enables access to multiple heterocycles similar to olefin-metathesis and will be discussed in the following part.…”

1,3-Dien-5-ynes: Versatile Building Blocks for the Synthesis of Carbo- and Heterocycles

“…In this regard, Jana has described a synthesis of phenanthrene derivatives by iron-catalyzed cycloisomerization of o-alkynylbiphenyls with an acyl substituent in the ortho position of the external aryl ring (Scheme 44). 130 Altough the transformation is formally analogous to the one depicted in Scheme 43, as it implies a formal intramolecular alkyne-carbonyl metathesis, a different mechanism is proposed. Thus, it is suggested to start with a nucleophilic attack of the alkyne over the iron-coordinated carbonyl group, leading to an alkenylic carbocation which subsequently generates an oxetene by intramolecular trapping with the oxygen.…”