Nickel‐Catalyzed, Cascade Cycloadditions of 1‐Ethynyl‐8‐halonaphthalenes with Nitriles: Synthesis, Structure, and Physical Properties of New Pyrroloarenes

Abstract

The reaction of 1-ethynyl-8-halonaphthalenes 1 with nitriles in the presence of the catalytic system [NiBr(2)(dppe)]/Zn (dppe=1,2-bis(diphenylphosphino)ethane) is found to produce unusual pyrroloarenes 2. The carbon-nitrogen triple bond in nitrile is activated twice, and five new bonds are formed in a one-pot transformation, which causes a pyrrole and two six-membered rings to be generated simultaneously. The scope and limitations of this reaction are examined. Similarly, alkyl-bridged diynes also furnish the corresponding polycycles. Diaryl-substituted cycloadducts 2 (R(1)=Ar) are fluxional, because of the restriction in rotation of the aryl groups. The rotational barrier is studied by performing (1)H NMR experiments at various temperatures. The structures of several compounds are determined by X-ray crystallographic analysis. The photophysical and electrochemical properties of the pyrroloarenes are also investigated.

Nickel‐Catalyzed Cascade Reactions

“…Wu's group reported a cascade cycloaddition reaction for the synthesis of pyrroloarene derivatives 34 in 16–84 % yield from 1‐ethynyl‐8‐halonaphthalenes 32 and nitriles 33 (Scheme 11). [29] The catalytic reaction was established in presence of 5 mol% NiBr 2 (dppe), 3 equiv. Zn at 110 °C for 12 h to achieve pyrroloarenes 34 and zethrene derivatives 35 where pyrroloarenes were formed in major quantity.…”

Metal‐Catalyzed Cascade Reactions: Useful Synthetic Tools for the Preparation of Polycyclic Arenes

“…Pyrroloarene 22 (R 1 = Ph, R 2 = Me) was first obtained as an unexpected product in studies whose goal was the optimization of reaction conditions when preparing zethrenes 21 . The catalytic system [NiBr 2 (dppe)/Zn] efficiently generated nitrile‐incorporated cycloadducts 22 , typically in moderate to good yields (Scheme ) . Importantly, this cascade reaction forms five new bonds to generate a pyrrole and two six‐membered rings in a one‐pot transformation.…”

Atom-economical synthesis of 1,2-bis(phosphine oxide)ethanes from calcium carbide with straightforward access to deuterium- and13C-labeled bidentate phosphorus ligands and metal complexes

“…Phosphine ligands play crucial roles in catalysis and organic chemistry. [46][47][48][49][50][51] DPPEO 2 and DPPE are commonly used singly in many catalytic transformations [52][53][54][55][56][57] or as Ni and Co complexes in cycloaddition reactions, [58][59][60][61][62][63][64] C-C bond formations [65][66][67] and polymerizations. 68 Moreover, DPPE complexes with gold and platinum show antitumor [69][70][71] and anticancer 72 activities.…”