Halogen-Bonding-Induced Hydrogen Transfer to C═N Bond with Hantzsch Ester

Abstract

Several bidentate dihydroimidazolines were prepared and investigated as catalysts for hydrogen transfer reduction of C═N bond with Hantzsch ester. Highly efficient reactions were observed for quinolines and imines with low catalyst loading of 2 mol %. The presence of halogen bonding was elucidated using NMR studies and isothermal calorimeric titrations. Binding constants of the XB donors were also measured using isothermal calorimeric titrations (ITC).

Halogen Bonding in Organic Synthesis and Organocatalysis

“…Later, Tan and co‐workers developed bidentate halogen‐bond donors based on dihydroimidazolines as catalysts for this reaction (Scheme ) . The substrate scope was also extended, as different imines could be reduced by the Hantzsch ester to give the corresponding amines in excellent yields (86–93 %) with low catalyst loadings (2–5 %).…”

New approaches to organocatalysis based on C–H and C–X bonding for electrophilic substrate activation

“…In 2014, the Tan group revisited the original study by Bolm and co-workers and re-investigated halogen bond induced hydrogen transfer to C=N bonds (Scheme 20) [91]. Various charged and uncharged electron-deficient iodoarenes were tested as potential catalysts, and chiral catalyst L25 was identified as the catalyst of choice.…”

Mit molekularem Iod katalysieren

“…Neben molekularem Iod haben andere Katalysatorsysteme wie iodierte Fluoraromaten oder Iodazoliumsalze Potenzial für die organische Katalyse. Das bestätigen Machbarkeitsstudien der letzten Jahre (Abbildung 7) 10,12,13. Möglicherweise entwickelt sich die Aktivierung über Halogenbrücken zu einem ebenso erfolgreichen Konzept wie die Wasserstoffbrückenaktivierung.…”