Lipase‐Catalyzed Kinetic Resolution of N‐Substituted 1‐(β‐Hydroxypropyl)indoles by Enantioselective Acetylation

A new, concise, and efficient route towards both antipodes of N‐(β‐hydroxypropyl)indoles is described. The key step is an enantioselective lipase‐mediated acetylation of racemic indolic alcohols [1‐(1H‐indol‐1‐yl)propan‐2‐ol, 1‐(2‐methyl‐1H‐indol‐1‐yl)propan‐2‐ol, and 1‐(5‐bromo‐1H‐indol‐1‐yl)propan‐2‐ol] with enol esters (vinyl acetate and isopropenyl acetate) as acyl group donors, performed under kinetically controlled conditions. A substantial influence of enzyme type, acyl group donor, and organic solvent on conversion rates and enantioselectivity of the enzymatic kinetic resolutions (EKRs) of the respective racemates was examined in detail. The best results in terms of enantioselectivity were obtained for the resolutions performed with native lipase from Pseudomonas fluorescens (PFL, Amano AK) in diisopropyl ether (DIPE) or tert‐butyl methyl ether (TBME) solution. To support the assignment of the absolute configurations of EKR products, chemical correlations with enantiomerically enriched analytical standards and single‐crystal X‐ray diffraction analysis were applied. Enzymatic kinetic resolution (EKR) of chiral N‐(β‐hydroxypropyl)indoles was achieved with excellent enantioselectivity (E >> 200) by applying Amano AK native lipase as the catalyst and a convenient transesterification method using vinyl acetate as the acetate group donor. The obtained highly enantioenriched indoles can be valuable chiral building blocks for medicinal and synthetic chemistry.