Indane-1,3-Dione: From Synthetic Strategies to Applications

Indane-1,3-dione is a versatile building block used in numerous applications ranging from biosensing, bioactivity, bioimaging to electronics or photopolymerization. In this review, an overview of the different chemical reactions enabling access to this scaffold but also to the most common derivatives of indane-1,3-dione are presented. Parallel to this, the different applications in which indane-1,3-dione-based structures have been used are also presented, evidencing the versatility of this structure.

Intramolecular rhodium-catalysed [2 + 2 + 2] cycloaddition of linear chiral N-bridged triynes: straightforward access to fused tetrahydroisoquinoline core

A route for the preparation of merged symmetrical tetrahydroisoquinolines with central chirality through a rhodium-catalyzed intramolecular [2 + 2 + 2] cycloaddition involving enantiopure triynes as substrates is described. The results show that linear triynes lacking a 3-atom tether can undergo efficient cyclisation. The N-tethered 1,7,13-triynes used in our approach were easily prepared from readily accessible chiral homopropargyl amides, the basic building blocks in our approach, which were efficiently obtained by diastereoselective addition of propargyl magnesium bromide to Ellman imines. Additional substitution at the benzene rings could be attained when substituted triynes at the terminal triple bonds were employed, giving access to more complex tetrahydroisoquinolines after the rhodium-catalyzed intramolecular [2 + 2 + 2] cycloaddition. Among the different transition-metal catalysts, the Wilkinson complex (RhCl(PPh₃)₃) afforded higher yields in the cyclisation of linear triynes; however, triynes bearing a Br substituent at the terminal positions underwent the cyclisation more efficiently in the presence of [RhCl(CO)₂]₂.

Recent Progress in Metal-Catalyzed [2+2+2] Cycloaddition Reactions

Metal-catalyzed [2+2+2] cycloaddition is a powerful tool that allows rapid construction of functionalized 6-membered carbo- and heterocycles in a single step through an atom-economical process with high functional group tolerance. The reaction is usually regio- and chemoselective although selectivity issues can still be challenging for intermolecular reactions involving the cross-[2+2+2] cycloaddition of two or three different alkynes and various strategies have been developed to attain high selectivities. Furthermore, enantioselective [2+2+2] cycloaddition is an efficient means to create central, axial, and planar chirality and a variety of chiral organometallic complexes can be used for asymmetric transition-metal-catalyzed inter- and intramolecular reactions. This review summarizes the recent advances in the field of [2+2+2] cycloaddition.

1 Introduction

2 Formation of Carbocycles

2.1 Intermolecular Reactions

2.1.1 Cyclotrimerization of Alkynes

2.1.2 [2+2+2] Cycloaddition of Two Different Alkynes

2.1.3 [2+2+2] Cycloaddition of Alkynes/Alkenes with Alkenes/Enamides

2.2 Partially Intramolecular [2+2+2] Cycloaddition Reactions

2.2.1 Rhodium-Catalyzed [2+2+2] Cycloaddition

2.2.2 Molybdenum-Catalyzed [2+2+2] Cycloaddition

2.2.3 Cobalt-Catalyzed [2+2+2] Cycloaddition

2.2.4 Ruthenium-Catalyzed [2+2+2] Cycloaddition

2.2.5 Other Metal-Catalyzed [2+2+2] Cycloaddition

2.3 Totally Intramolecular [2+2+2] Cycloaddition Reactions

3 Formation of Heterocycles

3.1 Cycloaddition of Alkynes with Nitriles

3.2 Cycloaddition of 1,6-Diynes with Cyanamides

3.3 Cycloaddition of 1,6-Diynes with Selenocyanates

3.4 Cycloaddition of Imines with Allenes or Alkenes

3.5 Cycloaddition of (Thio)Cyanates and Isocyanates

3.6 Cycloaddition of 1,3,5-Triazines with Allenes

3.7 Cycloaddition of Aldehydes with Enynes or Allenes/Alkenes

3.8 Totally Intramolecular [2+2+2] Cycloaddition Reactions

4 Conclusion

Multicomponent syntheses of 5- and 6-membered aromatic heterocycles using group 4-8 transition metal catalysts

In this Perspective, we discuss recent syntheses of 5- and 6-membered aromatic heterocycles via multicomponent reactions (MCRs) that are catalyzed by group 4-8 transition metals. These MCRs can be categorized based on the substrate components used to generate the cyclized product, as well as on common mechanistic features between the catalyst systems. These particular groupings are intended to highlight mechanistic and strategic similarities between otherwise disparate transition metals and to encourage future work exploring related systems with otherwise-overlooked elements. Importantly, in many cases these early- to mid-transition metal catalysts have been shown to be as effective for heterocycle syntheses as the later (and more commonly implemented) group 9-11 metals.

Ruthenium-Catalyzed Cycloadditions to Form Five-, Six-, and Seven-Membered Rings

Ruthenium-catalyzed cycloadditions to form five-, six-, and seven-membered rings are summarized, including applications in natural product total synthesis. Content is organized by ring size and reaction type. Coverage is limited to processes that involve formation of at least one C-C bond. Processes that are stoichiometric in ruthenium or exploit ruthenium as a Lewis acid (without intervention of organometallic intermediates), ring formations that occur through dehydrogenative condensation-reduction, σ-bond activation-initiated annulations that do not result in net reduction of bond multiplicity, and photochemically promoted ruthenium-catalyzed cycloadditions are not covered.

Gold(I)-Catalyzed Cascade Cyclization of Anilines with Diynes: Controllable Formation of Eight-Membered Ring-Fused Indoles and Propellane-Type Indolines

Heterocycle-fused indoles or indolines are distributed widely in a variety of natural products, bioactive agents, and pharmaceuticals. Herein, we describe the development of gold-catalyzed cascade reactions of anilines with diynes to form eight-membered ring-fused indoles and propellane-type indolines, both of which proceed through an intramolecular 5-endo-dig hydroamination followed by an 8-endo-dig cycloisomerization. Controllable formation of eight-membered ring-fused indoles and propellane-type indolines was achieved through selection of the ligands and/or solvents. Protic solvents such as alcohols or IPr ligand favored the formation of eight-membered ring-fused indoles, whereas the use of Buchwald's type ligands and/or nonpolar solvents gave propellane-type indoline predominantly. This reaction provides rapid access to two types of fused nitrogen heterocycles from simple aniline derivatives.

Nickel(ii)-mediated cyanamide–pyrazole coupling highlights distinct reactivity of NCNR2 and NCR nitrile ligands

The nickel(ii) center efficiently promotes the cyanamide–pyrazole coupling to give bis-chelate and tris-chelate products. The formation of the tris-chelate product for dialkylcyanamides is thermodynamically favorable.

Synthesis of Fluorescent Azafluorenones and Derivatives via a Ruthenium-Catalyzed [2 + 2 + 2] Cycloaddition

An original and mild synthetic route for the preparation of novel azafluorenones and derivatives via a ruthenium-mediated [2 + 2 + 2] cycloaddition of α,ω-diynes and cyanamides has been developed. This atom-economical catalytic process demonstrated remarkable regioselectivities to access fluorescent azafluorenone derivatives. The photophysical properties of azafluorenone derivatives have been evaluated, and photoluminescence phenomena at solid and liquid states have been highlighted.