[(NHC)Ni^IIH]‐Catalyzed Cross‐Hydroalkenylation of Cyclopropenes with Alkynes: Cyclopentadiene Synthesis by [(NHC)Ni^II]‐Assisted C−C Rearrangement

Abstract

Eine Hydroalkenylierungs/Umlagerungs‐Kaskade (HARC) mit Cyclopropen‐ und Alkinsubstraten wurde mithilfe von NHC‐Ni‐Katalysatoren realisiert. Wie C.‐Y. Ho und J.‐Q Huang in ihrer Zuschrift auf S. 5758 berichten, bietet dieses Verfahren eine neue, nachhaltige Route zu funktionalisierten Cyclopentadienen aus vielfältigen Cyclopropenen und Alkinen unter milden Bedingungen. Der Katalysator “greift sich” zunächst das Cyclopropen, woraufhin eine chemoselektive Alkininsertion und Umlagerung folgen.

Carbolong Chemistry: Planar CCCCX-Type (X = N, O, S) Pentadentate Chelates by Formal [3+1] Cycloadditions of Metalla-Azirines with Terminal Alkynes

“…For example, highly strained cyclopropenes can be used in [3+2] cycloaddition reactions with alkynes to form five-membered rings (Figure 1a, left). [13][14][15] Analogous reactions have also been reported in low-valent metal-mediated oxidative cyclometalation of alkynes, which can yield metallacyclopentadienes via the metalla-cyclopropenes (Figure 1a, right). 16,17 As another paradigm of strained azacyclic rings, 2H-azirines have successfully undergone diverse ring-expansion reactions by different bond cleavage modes, providing expedient approaches to five-membered N-heterocyclic skeletons (Figure 1b, left).…”

NHC/Nickel(II)‐Catalyzed [3+2] Cross‐Dimerization of Unactivated Olefins and Methylenecyclopropanes

“…The intermediates, such as cyclopropylmethyl‐Ni/Pd II , often undergo either β‐carbon eliminations or insertion of other partners, providing a general route to build hydro‐functionalized products. Recently, [NHC‐Ni(allyl)]BAr F (NHC=N‐heterocyclic carbene) was identified as a cross‐hydroalkenylation catalyst by using cyclopropenes and alkynes, and it involves a cyclopropane ring‐opening (Scheme c) . Thus, we become interested in [NHC‐Ni(allyl)]BAr F for MCP activation.…”

“…Our study commenced with a simple MCP, 1 a , and the terminal alkene 2 a by using the [IPr‐Ni(allyl)]BAr F catalyst reported for cycloisomerization and hydroalkenylation– (Table , entry 2). To our surprise, the postulated cross‐hydroalkenylation or β‐carbon‐elimination products were not observed, but a new [3+2] product ( 3 aa ) was observed for the first time.…”

Synthetic Applications of Cyclopropene and Cyclopropenone: Recent Progress and Developments

“…2H-phosphirenes were synthesized by various groups. [96] In 2017, Stephan's group [97] The five-membered carbocycles are very significant building blocks for organic synthesis, which are obtained from the intermolecular [3 + 2] cycloaddition of cyclopropenes. [98] Boger [99] and Nakamura [99] reported the transition metal-free cycloaddition of alkene, while [3 + 2] cycloaddition of cyclopropenes in the presence of weak nucleophiles such as enamines was not reported.…”