Three-Component Betti Condensation for Synthesis of Aminomethylnaphthols Incorporating Deoxy-isoequilenine Scaffold-Absolute Configuration and Application

Chiral aminomethylnaphthols have been prepared highly diastereoselective by means of three-component “Betti condensation”, using steroidal 2-naphthol analogue, synthesized from estrone. The use of 2-methoxybenzaldehyde or 2-pyridinecarboxaldehyde as aldehyde component and (S)-(–)-1-phenylethan-1-amine or (S)-(–)-1-(naphthalen-2-yl)ethan-1-amine, as chiral non-racemic amine component providing the diastereoselectivity, allowed the synthesis of structurally diverse aminomethylnaphthols. The latter easily form 1,3-dihydronaphthoxazines through reaction with formaldehyde. The absolute configurations of the new aminomethylnaphthols synthesized have been determined through advanced nuclear magnetic resonance (NMR) experiments and confirmed by X-ray crystallography. The chiral steroidal aminomethylnaphthols obtained as pure diastereoisomers have been evaluated as pre-catalysts in the enantioselective addition of diethylzinc to aldehydes with enantioselectivities of up to 97% enantiomeric excess (ee).

Keywords:
Betti condensation; chiral ligands; NOESY spectra; absolute configuration; enantioselectivity