✍ Scribed by Joerg Schwerdtfeger; Sabine Kolczewski; Berthold Weber; Roland Froehlich; Dieter Hoppe
No coin nor oath required. For personal study only.
1999 stereochemistry stereochemistry (general, optical resolution) O 0030
Stereoselective Deprotonation of Chiral and Achiral 2-Aminoalkyl Carbamates: Synthesis of Optically Active β-Amino Alcohols via 1-Oxy-Substituted Alkyllithium Intermediates.
-The reaction sequence to the title alcohols, consisting of the deprotonation of sterically demanding carbamates like (I), (IV), (VIII), and (XI), and introduction of an electrophile (MeI, silyl-and stannyl chlorides, CO 2 , alkoxycarbonyl chlorides, acid chlorides, esters, aldehydes, and ketones) permits the diastereoselective, general synthesis of more complex, optically active β-amino-α-hydroxy derivatives. The stereochemistry of the lithiation is greatly influenced by the complexing amine. The substrate-directed selection between the diastereotopic α-pro-R and pro-S protons in the TMEDA-assisted deprotonation is largely shifted towards pro-S-selectivity in the presence of (-)-sparteine. For the removal of the carbamoyl residue, three methods are developed: first, cleavage of the aminoacetal moiety and subsequent alkaline hydrolysis of the intermediate carbamic acid ester, second, reflux in 5 N aq.
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