*3.1. General Information*

1H and 13C NMR spectra were recorded on Inova 400 NMR instrument (Agilent, Santa Clara, CA, United States) with a 5 mm probe. Chemical shifts (δ) are reported in ppm, relative to the residual peaks of deuterated solvent signals.

HPLC-MS analyses were performed on an Agilent Technologies HP1100 instrument (Agilent, Santa Clara, CA, United States) coupled with an Agilent Technologies MSD1100 single-quadrupole mass spectrometer (Agilent, Santa Clara, CA, United States). A Phenomenex Gemini C18, 3 μm (100 × 3 mm) column was employed for the chromatographic separation: mobile phase H2O/CH3CN, gradient from 30% to 80% of CH3CN in 8 min, 80% of CH3CN until 22 min, and then up to 90% of CH3CN in 2 min; flow rate 0.4 mL min−<sup>1</sup> (Phenomenex, Torrance, CA, United States).

Chiral stationary phase (CSP)-HPLC analyses were performed on an Agilent Technologies Series 1200 instrument (Agilent, Santa Clara, CA, United States) using Daicel®chiral columns and *n*-hexane/2-propanol (*n*-Hex/IPA) mixtures (Daicel, Osaka, Japan).

Optical rotation measurements were performed on a polarimeter Schmidt+Haensch UniPol L1000 (Schmidt + Haensch GmbH & Co, Berlin, Germany).

Flash chromatography purifications were carried out using Merck silica gel 60 (230–400 mesh particle size). Thin layer chromatography was performed on Merck 60 F254 plates (Merck, Darmstadt, Germany).

Commercial reagents were used as received without additional purification, with exception of liquid aldehydes, which were distilled and stored under nitrogen atmosphere to avoid the formation of the corresponding acids. Dry methanol (Sure/Seal ™ bottle) was used to ensure a reproducible water content.

The diastereomeric and enantiomeric compositions were checked on the crude products against the corresponding racemic products, obtained under the same reaction conditions using racemic proline.
