NHC-Ni(II)-catalyzed cyclopropene-isocyanide [5 + 1] benzannulation.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Synthetic Organic Chemistry

Background:

• Isocyanides are versatile building blocks in chemical synthesis.
• Direct addition of isocyanides to unactivated cyclopropenes is synthetically challenging due to competing side reactions like homo-oligomerization.
• Existing methods often involve complex pathways or are limited by substrate scope.

Purpose of the Study:

• To develop a novel catalytic system for the direct [5+1] benzannulation of isocyanides with simple, unactivated cyclopropenes.
• To overcome the limitations of existing methods, particularly the competitive homo-oligomerization of isocyanides.
• To provide an efficient route to substituted aromatic amines and complex spirocyclic compounds.

Main Methods:

• Development and application of a (N-heterocyclic carbene)Ni(II) catalyst.
• Investigation of the reaction mechanism through substrate scope analysis and crystal structure determination of a key intermediate ([trans-(N-heterocyclic carbene)Ni(isocyanide)Br2]).
• Exploration of the cooperative effects of catalyst structure and substrate properties.

Main Results:

• The developed catalyst successfully enabled the direct [5+1] benzannulation of isocyanides with cyclopropenes.
• The reaction demonstrated a broad substrate scope, yielding diverse aromatic amine derivatives.
• Complex, unsymmetrical functionalized spiro-ring structures were synthesized efficiently.

Conclusions:

• The (N-heterocyclic carbene)Ni(II) catalyzed reaction provides a novel and efficient strategy for isocyanide-cyclopropene annulation.
• The success of the reaction is attributed to the synergistic interplay between the reactive cyclopropene, the sterically demanding N-heterocyclic carbene ligand, and the coordinating isocyanide.
• This approach complements existing synthetic methodologies like Dötz benzannulation and Semmelhack/Wulff synthesis, offering access to valuable chemical scaffolds.