Electrochemical Friedel-Crafts-type amidomethylation of arenes by a novel electrochemical oxidation system using a quasi-divided cell and trialkylammonium tetrafluoroborate.

Electrochemical Friedel-Crafts-type amidomethylation was successfully carried out by a novel electrochemical oxidation system using a quasi-divided cell and trialkylammonium tetrafluoroborates, such as iPr2NHEtBF4. Constant current electrolysis of 1,3,5-trimethoxybenzene or indoles in DMA containing 0.1 M iPr2NHEtBF4 using an undivided cell equipped with a Pt plate cathode and a Pt wire anode (a quasi-divided cell) resulted in selective formation of N-acyliminium ions of DMA at the anode, which reacted with arenes to give the corresponding amidomethylated products in good to high yields.

Synthesis of N-Boc-α-amino Acids from Carbon Dioxide by Electrochemical Carboxylation of N-Boc-α-aminosulfones.

Electrochemical reduction of N-Boc-α-aminosulfones in DMF using an undivided cell equipped with a Pt plate cathode and an Mg rod anode under atmospheric pressure of bubbling carbon dioxide through the solution under constant current conditions resulted in a reductive C-S bond cleavage with elimination of benzenesulfinate ion generating the corresponding anion species followed by fixation of carbon dioxide to give the corresponding N-Boc-α-amino acids in moderate to good yields.

Integrated Flow Synthesis of α-Amino Acids by In Situ Generation of Aldimines and Subsequent Electrochemical Carboxylation.

The synthesis of α-amino acids was carried out in a continuous flow system. In this system, aldimines were efficiently generated in situ via the dehydration-condensation of aldehydes with anilines in a desiccant bed column filled with 4 Å molecular sieves desiccant, followed by reaction with CO2 in an electrochemical flow microreactor to afford the α-amino acids in high to moderate yields. The present system can provide α-amino acids without using stoichiometric amounts of metal reagents or highly toxic cyanide reagents.

Electrochemical carboxylation of alpha-chloroethylbenzene in ionic liquids compressed with carbon dioxide.

Electrochemical carboxylation is conducted in ionic liquids compressed with carbon dioxide. It is found that the current efficiency increases with temperature and pressure. The diffusion coefficient of the substrate, which is obtained from the electrochemical measurements, also remarkably increases with temperature and pressure. The increase of the current efficiency is mainly explained by improvement in the mass transfer, and the promotion of the electrochemical carboxylation in the ionic liquid is achieved by pressurizing the carbon dioxide moderately.

Synthesis of isoindolobenzazepine alkaloids based on radical reactions or Pd(0)-catalyzed reactions.

Methods for synthesis of a ring system characteristic of isoindolobenzazepine alkaloids were studied. Synthesis of lennoxamine and a formal synthesis of chelenine were accomplished in a short route via radical or Pd(0)-catalyzed cyclization as the key step. An altenative approach based on a radical migration of a cyano group or Pd(0)-catalyzed carbonylation was also developed for both alkaloids.

Bioinspired synthesis of pentalene-based chromophores from an oligoketone chain.

We report a bioinspired synthesis of 2,5-dihydropentalene-based chromophores from an aliphatic oligoketone bearing 1,3- and 1,4-diketone subunits. Unlike the natural polyketone sequence, fused five-membered rings were formed via an intramolecular aldol condensation. A subsequent Knoevenagel condensation reaction with malononitrile furnished a multiply cross-conjugated π-system with low-lying LUMO levels. Furthermore, pentalenes obtained from a non-conjugated aliphatic chain exhibited visible absorption and solid-state fluorescence.

Stereoselective synthesis of 5-7 membered cyclic ethers by deiodonative ring-enlargement using hypervalent iodine reagents.

Stereoselective synthesis of 5-7 membered cyclic ethers was achieved by deiodonative ring-enlargement of cyclic ethers having an iodoalkyl substituent. The reaction took place readily under mild conditions using hypervalent iodine compounds and an acetoxy or a trifluoroacetoxy group was introduced into the rings depending on the hypervalent iodine reagent employed. The use of hexafluoroisopropanol (HFIP) as solvent is critical.

Rhodium-catalyzed ring-opening reactions of N-boc-azabenzonorbornadienes with amine nucleophiles.

In the presence of a rhodium catalyst (5 mol %) generated in situ from [Rh(cod)Cl](2) and (S,S')-(R,R')-C(2)-ferriphos (4a), the asymmetric ring-opening reaction of azabenzonorbornadienes (1a-m) with various aliphatic and aromatic amines (2a-l) proceeded with high enantioselectivity (up to >99% ee) to give the corresponding 1,2-diamine derivatives 3 in high yields. In the specific case of pyrrolidine as nucleophile, Et(3)NHCl was necessary as an additive for good reactivity and enantioselectivity. Additionally, a practical protocol was developed for the ring-opening of 1a with volatile amines at elevated temperatures and standard pressure, using R(2)NH(2)I and i-Pr(2)NEt. The experimental results showed that the nature of the chiral ligand has the significant impact on the reactivity of the catalyst and the use of excess amount (2.2 eq to Rh) of the chiral ligand plays an important role to improve the enantioselectivity in the present asymmetric reaction.