Synthesis of Acyl Terphenyls and Higher Polyaromatics via Base-Promoted C–H Functionalization of Acetylarenes with Arylacetylenes

Synthesis of 1,2,4,5-tetra-substituted benzenes via copper-catalyzed dimerization of γ,δ-unsaturated ketones

An efficient cyclization for the synthesis of 1,2,4,5-tetra-substituted benzenes via copper catalyzed dimerization of γ,δ-unsaturated ketones has been described. This one-pot procedure employs the γ,δ-unsaturated ketones as the sole substrate with multiple C-C bond formation. This protocol features broad substrate scope and provides a facile and robust method to construct polysubstituted benzene derivatives under mild conditions.

One-Pot Synthesis of Multiarylated Benzophenones via [3 + 2 + 1] Benzannulation of Ketones, Alkynes, and α,β-Unsaturated Carbonyls

In this study, we synthesized γ-phenyl-β,γ-unsaturated ketones in situ from acetophenones and phenylacetylenes under Trofimov's conditions using KOtBu in a dimethyl sulfoxide (DMSO) solvent. The obtained ketones reacted with α,β-unsaturated carbonyls in a one-pot manner, forming tri- or diarylated benzophenones. The present reaction proceeded efficiently by one-pot manipulation with a suitable carboxylic acid.

Substituted 9-Anthraldehydes from Dibenzocycloheptanol Epoxides via Acid-Catalyzed Epoxide Opening/Semipinacol Rearrangement

Starting from benzaldehyde derivatives, the corresponding dibenzocycloheptenol could be prepared in five steps. Under both substrate (secondary vs tertiary alcohol and the substituents on the aromatic ring(s)) and condition control, the subsequent epoxidation and acid-catalyzed epoxide opening/semipinacol rearrangement/aromatization afforded the corresponding 9-anthraldehydes in good yields, up to 88% over two steps. The presence of the electron-withdrawing group(s) on the aromatic ring(s) suppressed the rate of the epoxidation while the subsequent semipinacol rearrangement step required heating; the presence of the electron-donating group(s), on the other hand, frequently led to the decomposition during the epoxidation. From the mechanistic studies, the semipinacol rearrangement of the epoxide could precede the ionization at the bisbenzylic position, yielding the aldehyde intermediate. The ensuing dehydrative aromatization led to the formation of 9-anthraldehyde. Conversely, nucleophilic addition to the aldehyde and dehydrative aromatization with concomitant loss of formic acid led to anthracene.

Microwave-assisted organic acid–base-co-catalyzed tandem Meinwald rearrangement and annulation of styrylepoxides

A microwave-assisted acid and base co-catalyzed strategy shows very high efficiency in the tandem reaction for the conversion of styrylepoxides into [1,1′-biaryl]-3-carbaldehydes.

Base-Promoted SNAr Reactions of Fluoro- and Chloroarenes as a Route to N-Aryl Indoles and Carbazoles

KOH/DMSO-promoted C-N bond formation via nucleophilic aromatic substitution (S_NAr) between chloroarenes or fluoroarenes with indoles and carbazole under transition metal-free conditions affording the corresponding N-arylated indoles and carbazoles has been developed.

Transition-Metal-Free α-Vinylation of Enolizable Ketones with β-Bromostyrenes

An α-vinylation of enolizable ketones has been developed by using β-bromostyrenes and a KO tBu/NMP system. β,γ-Unsaturated ketones of E configuration were obtained in excellent yield and selectivity. Further synthetic possibilities are highlighted by one-pot functionalization via trapping of intermediate dienolates with alkyl, allyl, benzyl, and propargyl halides to generate quaternary centers. The reported transformation is believed to involve phenylacetylene and propargylic alcohol derivatives.

Acetylene-based two-step diastereoselective synthesis of bridgehead dihydro-oxadiazines using ketones and hydrazine as the only reactants

Bridgehead dihydro-1,3,4-oxadiazines are synthesized by the acid-catalyzed diastereoselective reaction of hydrazine with 6,8-dioxabicyclo[3.2.1]octanes, the products of the superbase-promoted self-organization of acetylene with ketones.

Acetylenes in the Superbase-Promoted Assembly of Carbocycles and Heterocycles

In this Account, we briefly discuss the recently discovered and rapidly developing superbase-promoted self-organization reactions of several equivalents of acetylenes and ketones to afford complex compounds that represent promising synthetic building blocks common in natural products. Notably, acetylenes play a special role in these reactions because of their dual (acting as an electrophile and a nucleophile) and flexible reactivity. These unique properties of acetylenes are elegantly expressed in superbasic media, where acetylenes are more deprotonated and their electrophilicity increases as a result of complexation with alkali metal cations, with simultaneous enhancement of the nucleophilic reactants due to desolvation. Under these conditions, acetylenes behave as a driving and organizing force toward other reactants. Various combinations of nucleophilic addition to the triple bond and acetylene deprotonation in the presence of other reactants with dual reactivity (e.g., ketones) enables the self-organization of complex molecular architectures that are inaccessible by conventional reactions. Herein we analyze recent achievements in this area concerning the reactions of acetylenes with ketones in superbasic KOH/DMSO-type systems that selectively afford synthetically and pharmaceutically valuable carbo- and heterocycles. Most of the reactions are triggered by the nucleophilic addition of deprotonated ketones (enolate anions) to acetylenes (superbase-catalyzed C-vinylation of ketones with acetylenes, which was recently introduced by our group into a toolkit of organic chemistry). The β,γ-ethylenic ketones thus formed can then take part in cascade processes with ketones and acetylenes to afford either carbocycles (e.g., hexahydroazulenones, acyl terphenyls, functionalized and cyclopentenols) or heterocycles (e.g., furans, benzoxepines, dioxabicyclo[3.2.1]octanes, and dioxadispiro[5.1.5.2]pentadecanes), depending on the structure of the reactants and the reaction conditions. Most of these compounds are selectively built from several equivalents of ketones and acetylenes in different combinations, and despite the presence of two or more asymmetric carbons in the products, they are generated as single diastereomers. When other nucleophiles (hydroxylamine, hydrazines, guanidine, and oximes) and ketones are involved in these self-organization processes, the intermediate β,γ-ethylenic ketones allow the formation of diverse heterocyclic systems (pyrroles, isoxazolines, pyrazolines, aminopyrimidines, and azabicyclo[3.1.0]hexanes). The discovered unique chemical transformations do not require transition metal catalysts and proceed under mild and operationally simple conditions. Most of these syntheses involve cascade addition reactions and therefore represent pot-, atom-, step-, and energy-saving processes that meet the requirements of green chemistry. The significance of the approach discussed herein is that it represents a viable alternative to existing classic and modern transition-metal-based catalytic syntheses of some fundamental carbo- and heterocycles. This is demonstrated by its employment of readily available, inexpensive starting materials like acetylenes and ketones and simple, widely accessible superbasic systems such as KOH/DMSO, which serves as a highly active universal catalyst and auxiliary. As shown in this Account, as this approach has developed, the number of preparatively attractive methods for the synthesis of diverse and potentially useful compounds has rapidly ballooned. The impressive experimental results presented in this Account will hopefully draw the attention of large circles of organic chemists involved in the design of rational and ecologically sound synthetic procedures and thus increase the application of these techniques in medicinal chemistry and materials science.

Transition-Metal-Free C-Vinylation of Ketones with Acetylenes: A Quantum-Chemical Rationalization of Similarities and Differences in Catalysis by Superbases MOH/DMSO and tBuOM/DMSO (M = Na, K)

Transition-metal-free C-vinylation of acetone with phenylacetylene catalyzed by superbases MOH/DMSO and tBuOM/DMSO (M = Na, K) has been theoretically evaluated in the B3LYP/6-311++G**//B3LYP/6-31+G* approach to rationalize similarities and differences in activity of the above catalytic systems. The close solvate surroundings of sodium and potassium tert-butoxides have been studied. Formation of tBuOM· nDMSO complexes and their structure and thermodynamic stability are discussed in comparison with similar complexes of alkali-metal hydroxides MOH· nDMSO. Activation barriers of the title reaction in the presence of tBuOM· nDMSO complexes are found to be less than those with MOH· nDMSO complexes participating.

t-BuOK-Mediated Oxidative Dehydrogenative C(sp3)-H Arylation of 2-Alkylazaarenes with Nitroarenes

The first transition-metal free and regioselective C(sp³)-H arylation of 2-alkylazaarenes with nitroarenes has been achieved via t-BuOK-mediated dehydrogenative C(sp³)-C(sp²) coupling. This reaction provides an efficient access to the biologically important and synthetically useful 2-benzyl-substituted azaarenes under mild conditions without the need of prefunctionalization of 2-alkylazaarenes or using the specialized arylating agents.