N‐Heterocyclic Carbene Catalyzed Enantioselective α‐Fluorination of Aliphatic Aldehydes and α‐Chloro Aldehydes: Synthesis of α‐Fluoro Esters,Amides, and Thioesters

The asymmetric fluorination of azolium enolates that are generated from readily available simple aliphatic aldehydes or α‐chloro aldehydes and N‐heterocyclic carbenes (NHCs) is described. The process significantly expands the synthetic utility of NHC‐catalyzed fluorination and provides facile access to a wide range of α‐fluoro esters, amides, and thioesters with excellent enantioselectivity. Pyrazole was identified as an excellent acyl transfer reagent for catalytic amide formation.     

Rhodium(I)‐Catalyzed Sequential C(sp)?C(sp3) and C(sp3)?C(sp3) Bond Formation through Migratory Carbene Insertion

A Rh^I‐catalyzed three‐component reaction of tert‐propargyl alcohol, diazoester, and alkyl halide has been developed. This reaction can be considered as a carbene‐involving sequential alkyl and alkynyl coupling, in which C(sp) C(sp³) and C(sp³) C(sp³) bonds are built successively on the carbenic carbon atom. The Rh^I‐carbene migratory insertion of an alkynyl moiety and subsequent alkylation are proposed to account for the two separate C C bond formations. This reaction provides an efficient and tunable method for the construction of all‐carbon quaternary center.     

Divergent C?H Insertion–Cyclization Cascades of N‐Allyl Ynamides

Gold carbene reactivity patterns were accessed by ynamide insertion into a C(sp³) H bond. A substantial increase in molecular complexity occurred through the cascade polycyclization of N‐allyl ynamides to form fused nitrogen‐heterocycle scaffolds. Exquisite selectivity was observed despite several competing pathways in an efficient gold‐catalyzed synthesis of densely functionalized C(sp³)‐rich polycycles and a copper‐catalyzed synthesis of fused pyridine derivatives. The respective gold–keteniminium and ketenimine activation pathways have been explored through a structure–reactivity study, and isotopic labeling identified turnover‐limiting C H bond‐cleavage in both processes.     

Rhodium(II) carbene-mediated modification of 2-deoxystreptamine surrogates

Rhodium(II)-catalyzed decomposition of carbene precursors grafted to the alcohol of diaminocyclopentanols promotes clean formation of a C-N bond via 1,6-insertion into an adjacent carbamate or azide. These modifications of 2-deoxystreptamine surrogates might give rise to aminoglycoside mimics where the two nitrogen atoms will be differentiated.     

One-pot synthesis of furo[2,3-h]quinoline and furo[2,3-h]isoquinoline derivatives using Fischer carbene complex

A new route for the synthesis of furo[2,3-h]quinoline and furo[2,3-h]isoquinoline derivatives have been explored through the coupling of carbene complexes with pyridine-bridged enynes. This reaction process, involving the annulation of both furan and benzene ring on to a pre-existing pyridine ring is highly efficient in the presence of triphenylphosphine as ligand additive.     

Ruthenium carbene complexes containing bidentate and tridentate PO ligands

Treatment of [Ru(CHR)Cl₂(PCy₃)₂] (Cy = cyclohexyl) with Tl[N(Pr₂ⁱPO)₂] and AgL_OEt (L_OEt⁻ = [CpCo{P(O)(OEt)₂}₃]⁻) afforded the Ru carbene complexes [Ru(CHPh)(PCy₃)Cl{N(Pr₂ⁱPO)₂}] (1) and [L_OEtRu(CHR)(PCy₃)Cl] (2), respectively. Chloride abstraction of complex 2 with TlPF₆ in MeCN afforded [L_OEtRu(CHPh)(PCy₃)(MeCN)][PF₆] (3). Complexes 1 and 2 are capable of catalyzing ring-closing metathesis of diethyl 1,2-diallylmalonate. The crystal structure of complex 2 has been determined.