Transmetalation of Alkylzirconocenes in Copper-Catalyzed Alkyl-Alkynyl Cross-Coupling Reactions

Visible-Light-Driven α-Aminoalkyl Radical-Mediated C(sp3)-C(sp) Cross-Coupling of Iodoalkanes and Alkynyl Bromides

We herein report a simple protocol for metal-free cross-coupling between unactivated alkyl iodides and terminal alkynyl bromides promoted by visible light. The salient features of this transformation are the utilization of an organic photocatalyst and commercially available tri-n-butylamine as a reductant. This protocol couples a variety of unactivated iodoalkanes containing different functional groups and with a variety of terminal alkynyl bromides under mild reaction conditions to afford the substituted alkynes in good yields.

Alkylzirconocenes in Organic Synthesis: An Overview

Organozirconium chemistry has found extensive applications in organic synthesis since its discovery in the last century. Alkyl­zirconocenes, which are easily generated by the hydrozirconation of alkenes with the Schwartz reagent, are widely utilized for carbon–carbon­ and carbon–heteroatom bond formation. This short review summarizes the progress to date on the applications alkylzirconocenes in organic synthesis.

1 Introduction

2 General Methods for Generating Alkylzirconocenes

3 Transformations of Alkylzirconocenes by Heteroatoms

4 Insertion of Unsaturated Groups into Alkylzirconocenes

5 Transmetalations

6 Cross-Coupling Reactions of Alkylzirconocenes

7 Photochemistry of Alkylzirconocenes

8 Bimetallic Reagents of Zirconium

9 Asymmetric Transformations

10 Applications of Alkylzirconocenes Generated from the Negishi Reagent

11 Conclusions and Outlook

Are Organozirconium Reagents Applicable in Current Organic Synthesis?

The search for mild, user-friendly, easily accessible, and robust organometallic reagents is an important feature of organometallic chemistry. Ideally, new methodologies employing organometallics should be developed with respect to practical applications in syntheses of target compounds. In this short review, we investigate if organozirconium reagents can fulfill these criteria. Organozirconium compounds are typically generated via in situ hydrozirconation of alkenes or alkynes with the Schwartz reagent. Alkyl and alkenylzirconium reagents have proven to be convenient in conjugate additions, allylic substitutions, cross-coupling reactions, and additions to carbonyls or imines. Furthermore, the Schwartz reagent itself is a useful reducing agent for polar functional groups.

1 Introduction

2 Synthesis and Generation of the Schwartz Reagent

3 Structure and Properties of Cp2Zr(H)Cl

4 Reactivity of Organozirconium Reagents

4.1 Asymmetric Conjugate Addition

4.2 Asymmetric Allylic Alkylations

4.3 Desymmetrization Reactions

4.4 Cross-Coupling Reactions

4.5 1,2-Additions

5 Conclusions

Chemoselective Cross-Coupling of gem-Borazirconocene Alkanes with Aryl Halides

The direct and chemoselective conversion of the carbon-metal bond of gem-dimetallic reagents enables rapid and sequential formation of multiple carbon-carbon and carbon-heteroatom bonds, thus representing a powerful method for efficiently increasing structural complexity. Herein, we report a visible-light-induced, nickel-catalyzed, chemoselective cross-coupling reaction between gem-borazirconocene alkanes and diverse aryl halides, affording a wide range of alkyl Bpin derivatives in high yields with excellent regioselectivity. This practical method features attractively simple reaction conditions and a broad substrate scope. Additionally, we systematically investigated a Bpin-directed chain walking process underlying the regioselectivity of alkylzirconocenes, thus uncovering the mechanism of the remote functionalization of internal olefins achieved with our method. Finally, DFT calculations indicate that the high regioselectivity of this reaction originates from the directing effect of the Bpin group.

Visible light promoted coupling of alkynyl bromides and Hantzsch esters for the synthesis of internal alkynes

A metal-free visible light promoted C(sp3)-C(sp) coupling reaction of alkynyl bromides and Hantzsch esters was developed, giving internal alkynes with primary, secondary, tertiary alkyl or other functional groups in good to high yields.