A Metathesis Approach to Aromatic Heterocycles

Abstract

The ring closing metathesis (RCM) reaction can be used to prepare substituted furans and pyrroles. By utilising a Pdcatalysed coupling reaction with methoxyallene, allylic alcohols and sulfonamides can be converted into substrates that are ideal precursors to ring closing metathesis. After the RCM reaction is complete, the addition of acid promotes an elimination of methanol to form the fully aromatised system.

Ringschlussmetathese: ein Schlüssel zur Arensynthese

“…[25] Uns gelang die Synthese von acyclischen Dien-Vorstufen (30, 33) über eine Palladium(ii)-katalysierte Kupplung eines Alkohols (oder eines Sulfonamids) mit Methoxyallen in guter Ausbeute (Schema 7). [26][27][28][29] Die RCM der gemischten Acetale (30) und Aminale (33) mithilfe des Grubbs-Katalysators der zweiten Generation 7 und die nachfolgende Umsetzung der Zwischenprodukte mit TFA zur Eliminierung von Methanol führte in guten Gesamtausbeuten zu den substituierten Furan-(31) und Pyrrolderivaten (34).…”

Synthesis of Dihydrofurans and Dihydropyrans with Unsaturated Side Chains Based on Ring Size‐Selective Ring‐Closing Metathesis

“…[27] Finally, Donohoe et al used a mixture of racemic 1 and its meso-diastereomer, after acetalization with methoxyallene and double RCM of the resulting tetraene, as a precursor for bisfuran. [28] Obviously, like for many other tri-, tetra-or polyenes, the use of metathesis precursors derived from 1 in RCM reactions is associated with either stereo-or regioselectivity issues. This aspect of olefin metathesis has recently been reviewed by us.…”

Five‐Membered Heterocycles: Furan

“…69). A range of different substitution patterns and functional groups are compatible with this sequence, such as the formation of both 70 and 72, employing also the Grubbs catalyst 71(Scheme 6.28) [69].…”