Cyclotryptophan Mycotoxins: Short Synthesis of the Desymmetrized meso-Chimonantine Core of Leptosin C

The desymmetrized meso-chimonantine core of leptosin C was prepared in a short stereoselective convergent sequence in 5 steps as the longest linear path from methyl l-tryptophan hydrochloride as starting material. The key step of this approach was a diastereoselective [4+2] cycloaddition between the bromooxindole and tryptophan derivatives allowing to define the adjacent quaternary benzylic centers in a high chemical yield

Diastereoselective arylation of l-proline derivatives at the 5-position

Diastereoselective introduction of nucleophiles into L-proline derivatives at the 5-position was achieved with suitable selection of N-protecting group. N-Methoxycarbonylated or benzyloxycarbonylated L-proline derivatives reacted with arene to give cis-arylated products. On the other hand, N-benzoylated L-proline derivative preferentially gave trans-arylated product which could be easily transformed into optically active C2-symmetrical pyrrolidine derivative. Such derivative 5, worked well as an organic activator in the asymmetric reduction of aromatic imines by Cl3SiH

High regioselectivity in electrochemical α-methoxylation of N-protected cyclic amines

N-Protecting groups of α-substituted cyclic amines strongly affected the regioselectivity in electrochemical methoxylation of these compounds. Namely, N-acyl derivatives were transformed into α′-methoxylated compounds, while N-cyano derivatives changed into α-methoxylated derivatives. Furthermore, Lewis acid catalyzed nucleophilic substitution of the α-methoxylated compounds protected with cyano group afforded α,α-disubstituted cyclic amines