A C-to-O atom-swapping reaction sequence enabled by Ni-catalyzed decarbonylation of lactones.

Advances in site-selective functionalization reactions have enabled single atom changes on the periphery of a complex molecule, but reaction manifolds that enable such changes on the core framework of the molecule remain sparse. Here, we disclose a strategy for carbon-to-oxygen substitution in cyclic diarylmethanes and diarylketones to yield cyclic diarylethers. Oxygen atom insertion is accomplished by methylene and Baeyer-Villiger oxidations. To remove the carbon atom in this C-to-O "atom swap" process, we developed a nickel-catalyzed decarbonylation of lactones to yield the corresponding cyclic diaryl ethers. This reaction was enabled by mechanistic studies with stoichiometric nickel(ii) complexes that led to the optimization of a ligand capable of promoting a challenging C(sp2)-O(aryl) reductive elimination. The nickel-catalyzed decarbonylation was applied to 6-8 membered lactones (16 examples, 32-99%). Finally, a C-to-O atom-swapping reaction sequence was accomplished on a natural product and a pharmaceutical precursor.

Λ-[Co((S,S)-dpen)3]3+ 2I-B(C6F5)4-: A Second Generation Air- and Water-Stable Chiral Solvating Agent for Chirality Sensing (dpen = NH2CHPhCHPhNH2).

When CDCl3 solutions of chiral racemic molecules containing moderately Lewis basic functional groups are treated with the chiral solvating agent (CSA) Λ-[Co((S,S)-dpen)3]3+ 2I-B(C6F5)4- (Λ-(S,S)-13+ 2I-B(C6F5)4-), baseline-resolved NMR signals are observed for the enantiomers (29 diverse analytes). Only 0.62-100 mol % loadings are required (avg 14.5 or 11.6% for 24 analytes common to all tested CSAs). The overall performance is superior to those reported earlier for analogous salts with 2X-BArf- counter anion sets [BArf = B(3,5-C6H3(CF3)2)4]; 1.0-100 mol % loadings, avg 32.6% (X = Cl) or 14.0% (X = I) for 24 common analytes) and a new 2TfO-B(C6F5)4- salt (1.1-100 mol % loadings; avg 31.0% for 24 common analytes), including extensions to prochirality sensing. The effect of the solvent (Δδ in CDCl3 > CD2Cl2) is analyzed. The new CSAs are prepared in two steps from Λ-(S,S)-13+ 3Cl- by standard anion metathesis recipes (90-98% overall). The broad analyte scope and modest loading requirements for the title CSA distinctly surpass those of others in the literature.

An Air- and Water-Stable Hydrogen-Bond-Donor Catalyst for the Enantioselective Generation of Quaternary Carbon Stereocenters by Additions of Substituted Cyanoacetate Esters to Acetylenic Esters.

The chiral enantiopure cobalt(III) complex Δ-[Co((S,S)-dpen)3 ]3+ 2Cl- B(C6 F5 )4 - (Δ-(S,S)-23+ 2Cl- B(C6 F5 )4 - ; dpen=1,2-diphenylethylenediamine) is an effective catalyst, together with pyridine (10 mol % each), for enantioselective additions of substituted cyanoacetate esters NCCH(R)CO2 R' to acetylenic esters R''C≡CCO2 R'''. In the resulting adducts NC(R'O2 C)C(R)CR''C=CHCO2 R''', C=C isomers in which the CO2 R''' moiety is trans to the new carbon-carbon bond dominate (avg. ratio 98:2). These are obtained in 70-98 % ee (avg. 86 %; data for optimum R' and R'''), as determined by 1 H NMR with the chiral solvating agent Λ-(S,S)-23+ 2I- B(3,5-C6 H3 (CF3 )2 )4 - . NMR experiments show that the cyanoacetate and acetylenic esters and pyridine can hydrogen bond to certain NH groups of the catalyst. Rates are zero order in the cyanoacetate and acetylenic esters as well as the catalyst, and implications are discussed.

The robust, readily available cobalt(iii) trication [Co(NH2CHPhCHPhNH2)3]3+ is a progenitor of broadly applicable chirality and prochirality sensing agents.

When NMR spectra of chiral racemic organic molecules containing a Lewis basic functional group are recorded in the presence of air and water stable salts of the cobalt(iii) trication [Co((S,S)-NH2CHPhCHPhNH2)3]3+ (23+), separate signals are usually observed for the enantiomers (28 diverse examples, >12 functional groups). Several chiral molecules can be simultaneously analyzed, and enantiotopic groups in prochiral molecules differentiated (16 examples). Particularly effective are the mixed bis(halide)/tetraarylborate salts Λ-23+ 2X-BArf- (X = Cl, I; BArf = B(3,5-C6H3(CF3)2)4), which are applied in CD2Cl2 or CDCl3 at 1-100 mol% (avg 34 and 14 mol%). Job plots establish 1 : 1 binding for Λ-23+ 2Cl-BArf- and 1-phenylethyl acetate (4) or 1-phenylethanol (10), and ca. 1 : 2 binding with DMSO (CD2Cl2). Selected binding constants are determined, which range from 7.60-2.73 M-1 for the enantiomers of 10 to 28.1-22.6 M-1 for the enantiomers of 4. The NH moieties of the C2 faces of the trication are believed to hydrogen bond to the Lewis basic functional groups, as seen in the crystal structure of a hexakis(DMSO) solvate of Λ-23+ 3I-. These salts rank with the most broadly applicable chirality sensing agents discovered to date.

Gigging Benzene.

Go Aggies! Go Chemikers! The word "gig" applies to a multipronged metal tool for hunting frogs and fish. It constitutes part of a rallying cry, "gig 'em" that inspires Texas A&M Aggies to victory in athletic and academic competitions. This Highlight examines recent victories in the C....._ C cleavage of benzene made possible by a four-pronged iridium gig that yields a "spring-loaded" norbornadiene-like structure with significant ring strain.

Ultrasound assisted one-pot synthesis of benzo-fused indole-4, 9-dinones from 1,4-naphthoquinone and α-aminoacetals.

A one-pot synthesis of benzo[f]indole-4,9-diones from 1,4-naphthoquinone with α-aminoacetals has been developed. This method provides a straightforward synthesis of benzo[f]indole-4,9-diones via intramolecular nucleophilic attack of aminoquinones to aldehydes under mild reaction conditions. The detailed mechanism was also investigated.