endo-Selective Iron Catalysts for Intramolecular Alkyne Hydrofunctionalization

Abstract

Metal–ligand cooperative iron complexes of the type [Fe­(Cp*)­(PR 2NPh 2)­(MeCN)]­PF6 (R = Cy, Ph) were synthesized and characterized. Both derivatives were active toward the intramolecular hydroamination of 2-ethynylaniline and hydroalkoxylation of 2-ethynylbenzyl alcohol. In the latter case, only the six-membered endo heterocycle isochromene was observed, which suggests that the alkyne is activated by a vinylidene mechanism. The reaction of [Fe­(Cp*)­(PCy 2NPh 2)­(MeCN)]­PF6 with phenylacetylene indeed afforded a complex that was characterized as a vinylidene, which implicates an analogous intermediate in the hydrofunctionalization mechanism.

Iron-Catalyzed Regiodivergent Hydrostannation of Alkynes: Intermediacy of Fe(IV)–H versus Fe(II)–Vinylidene

“…We planned to study the activating n Bu 3 SnH reagent and the substrate, RCC–H, by tuning the Lewis acid–base coordination sphere interactions in the half-sandwich iron­(II) system of Cp*Fe­(1,2-R 2 PC 6 H 4 X). The aim was to control the regioselectivity of catalytic alkyne hydrostannation.…”

“…To achieve such iron-based cooperative catalysis, the chemistry at an Fe–X site and the reactivity of the resultant organoiron species are of obvious significance. Although stoichiometric transformations of alkynes to vinylidene complexes have been known for several decades, activations of 1-alkynes by iron complexes to afford vinylidene species for catalysis have been only slightly reported . The present catalytically regenerated iron vinylidene intermediate might support exploring other important transformations involving alkyne functionalization, and these could expand the scope of iron catalysis in organic synthesis.…”

Transition Metal‐Catalyzed Hydroalkoxylation of Alkynes: An Overview

“…Blacquiere et al have reported intramolecular hydroalkoxylation of alkynols for the regioselective synthesis of endocyclic enol ether in good to excellent yield (Scheme 12). [19] They have synthesized the iron catalyst and have also shown for the first time that if a substrate is capable of performing both endo-and exo-dig mode of hydroalkoxylation, by the expense of this particular iron catalyst the reaction can be pushed in one direction i. e. endo-dig hydroalkoxylation. Thus, various alkynols 21 upon reaction with various iron-catalyst give corresponding cyclic enol ether 22.…”

A Catalytic Construction of Indoles via Formation of Ruthenium Vinylidene Species from N‐Arylynamides

“…The use of alkynes bearing a heteroatom nucleus instead of the carbon nucleus afforded heteroaromatics [4] such as benzofuran, which was provided from o ‐alkynylphenol by cyclization of hydroxyl group via the vinylidene intermediate [4b,d,e,g] . Syntheses of indole from o ‐alkynylaniline were realized via C−N bond formation triggered by an intramolecular attack of an amine moiety on vinylidene carbon [4b,e–i] . Tanaka [4g] and Saito [4h] independently developed a method for the synthesis of 3‐substituted indoles by 1,2‐rearrangement of silyl, aryl, alkyl, and acyl groups (Figure 1, Previous works).…”