Organocatalytic enantioselective synthesis of β-blockers: (S)-propranolol and (S)-naftopidil

An efficient enantioselective synthesis of β-adrenergic blockers (S)-propranolol and (S)-naftopidil with >98% ee using an l-proline-catalyzed α-aminoxylation of an aldehyde as a key step is described.

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(S)-3-(1′-Naphthoxy)propane-1,2-diolC13H14O3Ee = 98%[α]D25=+6.7 (c 1.05 MeOH)Source of chirality: asymmetric synthesisAbsolute configuration: (2S)

(S)-2-((1′-Naphthoxy)-methyl)oxiraneC13H12O2Ee = 98%[α]D25=-34.0 (c 1.52, MeOH)Source of chirality: asymmetric synthesisAbsolute configuration: (2S)

(S)-1-(Isopropylamino)-3-(1′-naphthoxy)propan-2-ol or (S)-propranololC16H21NO2Ee = 98%[α]D25=-9.8 (c 0.55, EtOH)Source of chirality: asymmetric synthesisAbsolute configuration: (2S)

(S)-1-[4-(2′-Methoxyphenyl)-piperazin-1-yl]-3-(1′-naphthoxy)-2-propanol or (S)-naftopidilC24H28N2O3Ee = 98%[α]D25=+4.7 (c 1.55, MeOH)Source of chirality: asymmetric synthesisAbsolute configuration: (2S)