The Schöllkopf chiron and transition metal mediated reactions, a powerful combination for stereoselective construction of cyclic α-quaternary-α-amino acid derivatives

A new oxidatively stable ligand for the chiral functionalization of amino acids in Ni(II)-Schiff base complexes

A new oxidatively stable (S)-N-benzylproline-derived ligand ((S)-N-(2-benzoyl-5-tert-butylphenyl)-1-benzylpyrrolidine-2-carboxamide) and its Ni(II)-Schiff base complexes formed of glycine, serine, and dehydroalanine are reported. A bulky tert-butyl substituent in the phenylene fragment precludes unwanted oxidative dimerization of the Schiff base complex, making it suitable for targeted electrochemically induced oxidative modification of the amino acid side chain. Experimental and DFT studies showed that the additional tert-butyl group increases the dispersion interactions in the Ni coordination environment making the complexes more conformationally rigid and provides a higher level of thermodynamically controlled stereoselectivity as compared to the parent Belokon complex. Additionally, functionalization with the tert-butyl group significantly enhances the reactivity of the deprotonated glycine complex towards electrophiles as compared to the anionic species formed from the original Belokon complex. Solubility of the t-Bu-containing ligand and its Schiff base complexes is increased, facilitating scaling-up the reaction procedure and isolation of the functionalized amino acid.

Bicyclo[6.1.0]nonyne and tetrazine amino acids for Diels–Alder reactions

Here we report a general method for the de novo synthesis of a bicyclo[6.1.0]nonyne group containing an amino acid, and used Marfey's reagent for chiral analysis.

Diversity-Oriented Approaches to Polycyclics and Bioinspired Molecules via the Diels-Alder Strategy: Green Chemistry, Synthetic Economy, and Beyond

We describe diverse approaches to various dienes and their utilization in the Diels-Alder reaction to produce a variety of polycycles. The dienes covered here are prepared by simple alkylation reaction or via the Claisen rearrangement or by enyne metathesis of alkyne or enyne building blocks. Here, we have also included the Diels-Alder chemistry of dendralenes, a higher analog of cross-conjugated dienes. The present article is inclusive of o-xylylene derivatives that are generated in situ starting with benzosultine or benzosulfone derivatives. The Diels-Alder reaction of these dienes with various dienophiles gave diverse polycyclic systems and biologically important targets.

Intramolecular hydroamination of dithioketene acetals: an easy route to cyclic amino acid derivatives

Catalytic intramolecular hydroamination of dithioketene acetals was developed for the synthesis of cyclic amino acid derivatives. Triggered by the addition of a catalytical amount of n-BuLi, the reaction proceeds to give proline and pipecolic acid derivatives in excellent yields and diastereoselectivity.

Intramolecular anodic olefin coupling reactions: using competition studies to probe the mechanism of oxidative cyclization reactions

A competition experiment was designed so that the relative rates of anodic cyclization reactions under various electrolysis conditions can be determined. Reactions with ketene dithioacetal and enol ether-based substrates that use lithium methoxide as a base were shown to proceed through radical cation intermediates that were trapped by a sulfonamide anion. Results for the oxidative coupling of a vinyl sulfide with a sulfonamide anion using the same conditions were consistent with the reaction proceeding through a nitrogen-radical.

Intramolecular anodic olefin coupling reactions and the synthesis of cyclic amines

Anodic olefin coupling reactions using a tosylamine trapping group have been studied. The cyclizations are favored by the use of a less-polar radical cation and more basic reaction conditions. The most significant factor for obtaining good yields of cyclic product is the use of the more basic reaction conditions. However, a number of factors including the nature of both the solvent and the electrolyte used can influence the yield of the cyclizations. The cyclizations allow for the rapid synthesis of both substituted proline and pipecolic acid type derivatives.

Recent Progress on the Stereoselective Synthesis of Cyclic Quaternary alpha-Amino Acids

The most recent papers describing the stereoselective synthesis of cyclic quaternary alpha-amino acids are collected in this review. The diverse synthetic approaches are classified according to the size of the ring and taking into account the bond that is formed to complete the quaternary skeleton.