Simplified Version of the Eschweiler-Clarke Reaction.

The traditional Eschweiler-Clarke reaction is a three-component process involving formaldehyde, amine, and formic acid. In this work, we showed that the reductive potential of formaldehyde was sufficient to provide methylation of secondary amines in the absence of acidic additives. Various acid-sensitive moieties remain intact under developed conditions. The scalability of the elaborated approach was shown for several products. Synthesis of the antifungal agent butenafine demonstrated the preparative utility of the developed approach.

Redox Condensations of o-Nitrobenzaldehydes with Amines under Mild Conditions: Total Synthesis of the Vasicinone Family.

A total synthesis of the vasicinone family of natural products from bulk chemicals was developed. Reductive condensation of o-nitrobenzaldehydes with amines utilizing iron pentacarbonyl as a reducing agent followed by subsequent oxidation leads to a great variety of polycyclic nitrogen-containing heterocycles under mild conditions. Enantiomerically pure vasicinone, rutaecarpine, isaindigotone, and luotonin were synthesized from readily available starting materials like hydroxyproline, nitrobenzaldehyde, pyrrolidine, and piperidine in two to four operational steps without chromatography. The antifungal activity of all products was tested.

Planar-chiral arene ruthenium complexes: synthesis, separation of enantiomers, and application for catalytic C-H activation.

Heating tert-butyl-tetraline with [(p-cymene)RuCl2]2 produces the racemic complex [(arene)RuCl2]2, which can be separated into enantiomers by chromatography of its diastereomeric adducts with chiral phosphine ligand. The resolved chiral complex catalyzes C-H activation of N-methoxy-benzamides and their annulation with N-vinyl-pivaloyl amide giving dihydroisoquinolones in 50-80% yields and with 40-80% enantiomeric excess.

Rhodium complexes with planar-chiral cyclopentadienyl ligands: synthesis from tert-butylacetylene and catalytic performance in C-H activation of arylhydroxamates.

The rhodium complex [(C5H2tBu2CH2tBu)RhCl2]2 with an asymmetric cyclopentadienyl ligand was prepared in 95% yield by the reaction of [(cod)RhCl]2 with tert-butylacetylene in the presence of AlCl3. A similar reaction in the presence of InBr3 gave the cationic fulvene complex [(C5H2tBu2 = CHtBu)Rh(cod)]InBr4 (70%), which can add alcohols ROH and produce more bulky catalysts [(C5H2tBu2CH(OR)tBu)RhCl2]2. The enantiomers of these planar-chiral complexes were separated by thin-layer chromatography in the presence of L-phenylglycinol. The complexes catalyze the reactions of arylhydroxamates with alkenes giving dihydroisoquinolones in excellent yields (80-90%), but with moderate enantioselectivity (typically 20-50% ee).

Planar Chiral Rhodium Complex Based on the Tetrahydrofluorenyl Core for Enantioselective Catalysis.

A simple four-step route to a chiral tetrahydrofluorenyl rhodium catalyst from naturally occurring (-)-α-pinene was developed. Our approach does not use multistep and time-consuming procedures such as chiral HPLC or diastereomeric resolution. The key to success lies in the face-selective coordination of rhodium to the sterically hindered tetrahydrofluorenyl ligand, giving only one diastereomeric complex. This catalyst proved to be highly efficient for asymmetric C-H annulation of aryl hydroxamates with alkenes (yield up to 95%, 91% ee) at low loading (up to 0.4 mol % based on Rh).

Sodium Hypophosphite as a Bulk and Environmentally Friendly Reducing Agent in the Reductive Amination.

NaH2PO2 was found to promote reductive amination. Being nontoxic, stable, environmentally benign, and available in bulk amounts, this reducing agent showed a powerful potential to compete with classical reductants applied in the target process. An E factor of 1 was achieved for the substrate scope. Different carbonyl compounds reacted with amines under the developed conditions. The reaction demonstrated a great compatibility with a wide range of functional groups. Reaction conditions were scaled up to 200-fold.