ABSTRACT
The enantioselective organocatalytic conjugate alkenylation of ß-substituted alkenyl benzimidazoles afforded ß-stereogenic 2-alkyl benzimidazole derivatives in excellent enantioselectivities. Chiral binaphthols were effective catalysts for promoting the nucleophilic addition of bench-stable alkenyl trifluoroborate salts under mild conditions, expanding their applications by utilizing C=N-containing azaarenes as activating groups. The synthetic utility of this strategy is demonstrated by conversions into several useful enantiomerically enriched benzimidazole building blocks.
Subject(s)
Benzimidazoles , Salts , Catalysis , Molecular Structure , StereoisomerismABSTRACT
A chiral phosphoric acid-catalyzed kinetic resolution of tertiary allylic alcohols was developed to provide structurally valuable enantioenriched 2,2-disubstituted tetrahydrofurans, tetrahydropyrans, and oxepane. A variety of tertiary allylic alcohols were resolved with selectivity factors of ≤120. A tertiary allylic carbocationic intermediate mediates the enantioselective intramolecular substitution to achieve high regio- and enantioselectivity. A gram-scale reaction with low catalyst loading and subsequent transformations of the recovered alcohols and products demonstrated the utility of this method.
ABSTRACT
Readily available potassium alkynyltrifluoroborates were used for organocatalytic asymmetric conjugate alkynylation of ß-enaminones. The interception of a modified binaphthol catalyst and in situ generated organodifluoroboranes proved important to access functionalized ß-alkynyl-ß-amino carbonyls and derivatives with improved chemo-reactivity and enantio-induction. Mechanistic studies revealed the impact of molecular sieves on efficiency and stereocontrol. The products undergo additional functionalization to yield a diverse set of valuable ß-alkynyl-ß-amino carbonyl scaffolds.
