Mikel Oiarbide

A scalable procedure for the synthesis of 4,6‐difluorotryptophan is reported based on a deaminative coupling of a 4,6‐difluorogramine with 2‐benzylthio‐1,5‐dihydro‐4 H ‐imidazolone as glycine equivalent. Thus prepared 4,6‐difluorotryptophan was incorporated into the C‐terminal domain of the HIV‐1 capsid protein (CA‐CTD), and 19 F spectra of the 4,6‐difluoro Trp CA CTD were recorded and compared to the singly fluorinated counterparts.

Chiral Brønsted base (BB) catalyzed asymmetric transformations constitute an important tool for synthesis. A meaningful fraction of these transformations proceeds through transiently generated enolate intermediates, which display quite versatile reactivity against a variety of electrophiles. Some years ago, our group became interested in developing BB‐catalyzed asymmetric reactions of enolizable carbonyl substrates that involve π‐extended enolates in which, besides control of reaction diastereo and enantioselectivity, the site‐selectivity control is an additional issue in most cases. In the examples covered in this account the opportunities deployed, and the challenges posed, by these methods are illustrated, with a focus on the generation of quaternary carbon stereocenters. In the way, new bifunctional BB catalysts as well as achiral templates were developed that may find further applications.