Brønsted-Acid-Catalyzed One-Pot Synthesis of β,β-Diaryl Esters: Direct Regioselective Approach to Diverse Arrays of 3-Aryl-1-indanone Cores

A three-component, solvent-dependent, Brønsted-acid-catalyzed reaction of benzaldehydes, silyl enolates and arene nucleophiles has been developed for the synthesis of potential drug candidate 3-aryl-1-indanones. This reaction features the formation of three C-C bonds, high regioselectivity in a one-pot strategy, broad substrate generality, facile scalability (1.04g), high functional group tolerance and viable substrates. The β-O-silyl ethers generated in-situ from the Mukaiyama aldol reaction were subjected to acid-catalyzed benzylic arylation with strong as well as weak nucleophiles, and the resultant β,β-diaryl esters can undergo a third C-C bond formation with excellent regioselectivity through intramolecular cyclization to afford the indanone products in the same pot. Detailed mechanistic insight leads to a feasible reaction pathway. This transformation opens up a practical and adaptable approach to producing a variety of synthetically valuable transformations and enable the synthesis of medicinally valuable (R)-tolterodine and (+)-indatraline.

Friedel-Crafts-Type Acylation and Amidation Reactions in Strong Brønsted Acid: Taming Superelectrophiles

In this review, we discuss Friedel-Crafts-type aromatic amidation and acylation reactions, not exhaustively, but mainly based on our research results. The electrophilic species involved are isocyanate cation and acylium cation, respectively, and both have a common ⁺C=O structure, which can be generated from carboxylic acid functionalities in a strong Brønsted acid. Carbamates substituted with methyl salicylate can be easily ionized to the isocyanate cation upon (di)protonation of the salicylate. Carboxylic acids can be used directly as a source of acylium cations. However, aminocarboxylic acids are inert in acidic media because two positively charged sites, ammonium and acylium cation, will be generated, resulting in energetically unfavorable charge-charge repulsion. Nevertheless, the aromatic acylation of aminocarboxylic acids can be achieved by using tailored phosphoric acid esters as Lewis bases to abrogate the charge-charge repulsion. Both examples tame the superelectrophilic character.

Umpolung Chemo- and Regioselective Cascade Addition of Diethylzinc to α-Diketones Followed by Intramolecular Michael Reaction: Stereoselective Synthesis of Highly Substituted 1- Indanones

Herein we report an efficient stereoselective umpolung 1,2-addition of Et₂Zn onto α-diketones followed by intramolecular cascade Michael cyclization. This strategy effectively delivers a broad range of substituted 1-indanones in excellent yields in a chemo- and regioselective fashion. Additionally, we performed a variety of synthetic transformations on the 1-indanone products. Furthermore, a hitherto-unexplored asymmetric variant of this methodology that provides up to 94:6 er using an easily accessible cinchona alkaloid ligand has been addressed.

Rhodium(iii)-catalyzed synthesis of 3-trifluoromethylindanones from N-methoxybenzamides via C–H activation and Claisen/retro-Claisen reaction

An efficient synthesis of 3-trifluoromethylindanones via C–H annulation of N-methoxybenzamides with β-trifluoromethyl-α,β-unsaturated ketones under Rh(iii)-catalysis is described.

Palladium(ii)-catalyzed synthesis of indenones through the cyclization of benzenecarbaldehydes with internal alkynes

The palladium(ii)-catalyzed carbocyclization of benzenecarbaldehydes with internal alkynes to afford 2,3-disubstituted indenones was reported. The annulation reaction proceeded through the transmetalation of Pd(ii) with an aromatic aldehyde and the insertion of internal alkynes, followed by cyclization via the intramolecular nucleophilic addition of intermediate organopalladium(ii) species to the aldehyde group. This reaction proceeded in moderate to good yields with high regioselectivity.

Brønsted Acid-Mediated Domino One-Pot Dual C-C Bond Formation: Chemoselective Synthesis of Fused Tricyclic Ketones

A chemoselective synthesis of fused novel tricyclic motifs via a facile domino intramolecular cyclization is presented. The strategy enables the formation of dual C-C bond via intramolecular Friedel-Crafts alkylation followed by acylation to accomplish fused tricyclic ketones. Significantly, these fused tricyclic compounds are ubiquitous and constitute major structural cores of natural products.

Oxidative annulations triggered by a simple Lewis acid: facile synthesis of benzofurans

The first example of Lewis acid promoted efficient one-pot synthesis of benzofurans is presented.

Tandem buildup of complexity of aromatic molecules through multiple successive electrophile generation in one pot, controlled by varying the reaction temperature

While some sequential electrophilic aromatic substitution reactions, known as tandem/domino/cascade reactions, have been reported for the construction of aromatic single skeletons, one of the most interesting and challenging possibilities remains the one-pot build-up of a complex aromatic molecule from multiple starting components, i.e., ultimately multi-component electrophilic aromatic substitution reactions. In this work, we show how tuning of the leaving group ability of phenolate derivatives from carbamates and esters provides a way to successively generate multiple unmasked electrophiles in a controlled manner in one pot, simply by varying the temperature. Here, we demonstrate the autonomous formation of up to three bonds in one pot and formation of two bonds arising from a three-component electrophilic aromatic substitution reaction. This result provides a proof-of-concept of our strategy applicable for the self-directed construction of complex aromatic structures from multiple simple molecules, which can be a potential avenue to realize multi-component electrophilic aromatic substitution reactions.

One-pot C–C/C–O bond formation: synthesis of spirocyclic lactones

An efficient and practical method for the synthesis of novel spiro(tri or tetra)cyclic lactones via the formation of C–C and C–O bonds in one-pot is presented.