Metal-Dependent Umpolung Reactivity of Carbenes Derived from Cyclopropenes

Abstract

Summary Metal carbenes, divalent carbon species, are versatile intermediates that enable novel synthetic pathways. These species exhibit either electrophilic or nucleophilic character, depending on the carbene and metal fragments. Although the metal carbene reactivity is regulated by the metal, the umpolung of carbene reactivity by changing metal remains challenging. Here, we report a unique metal-induced de novo umpolung of carbene reactivity, wherein a carbene precursor can be transformed into either an electrophilic carbene or a nucleophilic carbenoid, depending on the metal promoters. Thus, a chemodivergent reaction of isatins and cyclopropenes is developed. Under the promotion of Zn 2+ halides, a nucleophilic zinc carbenoid is formed and trapped by isatins to produce oxindole derivatives containing an alkenyl halide moiety. Using Rh 2 (esp) 2 as a catalyst, the reaction delivers oxindoles carrying a dihydrofuran unit. This work provides a facile approach to harness the metal carbene reactivity and is critical for the development of diversity-oriented synthesis.

Highly Enantioselective Trapping of Carboxylic Oxonium Ylides with Imines for Direct Assembly of Enantioenriched γ-Butenolides

“…Recently, we uncovered a unique reaction of cyclopropene alcohols with isatins, in which the oxonium ylides from cyclopropene alcohols were captured as reactive ketones at the vinylogous site (Scheme 1b). 25 This seminal discovery demonstrated that cyclopropene, a versatile precursor of donor-type vinyl carbenes, could be applied to ylide-trapping chemistry. Inspired by this study and the transition-metal-catalyzed cycloisomerization of cyclopropene carboxylic acids by Komendantov and Dominin, 26 we anticipated that the we could employ the stable, readily available cyclopropene carboxylic acids 27 to serve as new types of precursors of cyclic carboxylic oxonium ylides.…”

Rhodapentalenes: Pincer Complexes with Internal Aromaticity

“…The reactions of 2a with 8-hydroxyquinoline, PPh 3 , and pyridine N -oxide indicate the pronounced electrophilicity and lability of the rhodium-carbon bonds in rhodapentalenes and are consistent with the chemical behavior of rhodium carbene moieties (Berry, 2012, Tindall et al., 2018, Zhang et al., 2019). The steric crowding of the bulky phosphonium group adjacent to the C1-position may account for the C7-position being the sole active site in the reactions of 2a .…”

Unusual Synthesis of Triosmium Carbene Clusters by Tandem Activation of Chlorohydrocarbons and Heterocyclic Amines

“…Cluster 3 , unlike most organometallic carbenes, [25–29] is stable in the solution up to ∼100 °C suggesting an idea that the Os−C carbene binding energy in 3 is unusually high. This assumption is confirmed by the fact that the attempt to replace the carbene ligand with PPh 3 in cluster 3 leads to substitution of one CO group instead.…”