Concave Reagents. 20. Sterically Shielded m-Terphenyls as Selective Agents in General Protonations(1)

Asymmetric synthesis of diverse glycolic acid scaffolds via dynamic kinetic resolution of α-keto esters

The dynamic kinetic resolution of α-keto esters via asymmetric transfer hydrogenation has been developed as a technique for the highly stereoselective construction of structurally diverse β-substituted-α-hydroxy carboxylic acid derivatives. Through the development of a privileged m-terphenylsulfonamide for (arene)RuCl(monosulfonamide) complexes with a high affinity for selective α-keto ester reduction, excellent levels of chemo-, diastereo-, and enantiocontrol can be realized in the reduction of β-aryl- and β-chloro-α-keto esters.

Dynamic kinetic resolution of α-keto esters via asymmetric transfer hydrogenation

The dynamic kinetic resolution of β-aryl α-keto esters has been accomplished using a newly designed (arene)RuCl(monosulfonamide) transfer hydrogenation catalyst. This dynamic process generates three contiguous stereocenters with remarkable diastereoselectivity through a reduction/lactonization sequence. The resulting enantioenriched, densely functionalized γ-butyrolactones are of high synthetic utility, as highlighted by several secondary derivatizations.

Concave Reagents. New 2'-Substituted m-Terphenyls

New 2'-substituted 2,2'',6,6''-tetramethyl-1,1':3',1''-terphenyls have been synthesized. Solubility of concave acids 4b-6b could be enhanced by substitution in 4 and 4'' position, allowing the study of hydrogen-bonded heterodimers. Concave acids show larger binding constants for 2-amidopyridines 7 than non-macrocyclic ones, probably due to the prevention of homodimer formation by the macrocyclic shielding. New 2,6-diarylbenzyl alcohols 1d, 8d and 9d have been synthesized and tested in protonation reactions. New functional groups were introduced into the 2' position: OH (phenols 1f and 12f) and NH2 (aniline 1j). The basicity of aniline 1j in ethanol was determined by titration and was compared to other bases. Also sulfonic acids 1l and 17l were prepared, and the corresponding methyl esters 1m and 17m were tested as methylating agents.

Novel anionic annelation tactics for construction of fused heteroaromatic frameworks. 1. Synthesis of 4-substituted pyrazolo[3,4-c]quinolines, 9-substituted pyrazolo[3,4-c]quinolines, and 1,4-dihydrochromeno[4,3-c]pyrazoles

4-Substituted pyrazolo[4,3-c]quinolines 4a-i and 6a-b were prepared from pyrazole 3 whereas 9-substituted pyrazolo[3,4-c]quinolines 9a-d and 17 were prepared from pyrazole 13 utilizing anionic annelation techniques. 1,4-dihydrochromeno[4,3-c]pyrazoles 7a-c were accessed from pyrazole 3, extending the method for the synthesis of 4a-i.