Halogenated catechols from cycloaddition reactions of η4-(2-ethoxyvinylketene)iron(0) complexes with 1-haloalkynes

Abstract

1-chloroalkynes and 1-bromohexyne undergo cycloaddition reactions with ethoxyvinylketeneiron(0) complexes to form chloro and bromocatechols. With most substituents, the halogen is incorporated ortho to the phenolic hydroxyl group regioselectively. With chloroethyne, chlorohexyne, and methyl chloropropiolate, the reverse regioselection is observed. Ab initio calculations reveal that the products are, in most cases, nearly isoenergetic, which indicates that the intermediate ketene-alkyne adduct geometry must be important in determining the product distribution.

Recent advances in the iron-catalyzed cycloaddition reactions

“…Recently, stoichiometric cycloaddition reactions of alkynes or 1-haloalkynes with vinylketeneiron(0) complexes affording the catechol derivatives were described by Schnatter and co-workers [97,98] (Scheme 46). However, two regioisomers with moderate yields were generally obtained and the reaction with several alkyl, silyl and aryl alkynes produced alkyne trimers as the major products.…”

Iron(0) Promotes Aza Cyclization of an Elusive Ferrocenylketene

“…The synthesis and study of ferrocenylvinylketenes have been restricted to just a few examples, which could be due to their high predicted instability. , Tidwell and co-workers developed the synthesis of ferrocenylketenes through a Wolff rearrangement, providing evidence for the presence of this intermediate using time-resolved IR spectroscopy and trapping it by reaction with n -BuNH 2 to give the corresponding amide. An efficient alternative for synthesizing these kind of masked intermediates as stable and isolable compounds could be the use of iron(0) complexes, − starting from available α,β-unsaturated ferrocenyl ketones. Such ligands can be versatile precursors that can incorporate a wide variety of groups, including aza-heterocyclic rings.…”