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Brominations of Cyclic Acetals from α‐Amino Acids and α‐ or β‐Hydroxy Acids with N ‐Bromosucinimide
Author(s) -
Zimmermann Jürg,
Seebach Dieter
Publication year - 1987
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19870700423
Subject(s) - chemistry , halogenation , electrophile , serine , ring (chemistry) , amino acid , medicinal chemistry , stereochemistry , organic chemistry , catalysis , biochemistry , enzyme
The preparation of novel electrophilic building blocks for the synthesis of enantiomerically pure compounds (EPC) is described. Thus, the 2‐( tert ‐butyl)dioxolanones, ‐oxazolidinones, ‐imidazolidinones, and ‐dioxanones obtained by acetalization of pivalaldehyde with 2‐hydroxy‐, 3‐hydroxy‐, or 2‐amino‐carboxylic acids are treated with N ‐bromosuccinimide under typical radical‐chain reaction conditions (azoisobuytyronitril/CCl 4 /reflux). Products of bromination in the α‐position of the carbonyl group of the five‐membered‐ring acetals are isolated or identified ( 2, 5 , and 8 ; Scheme 1 ). The dioxanones are converted to 2 H , 4 H ‐dioxinones under these conditions ( 12 , 14 , 15 , 21 , and 22 ; Schemes 2 and 3 ). The products can be converted to chiral derivatives of pyruvic acid (methylidene derivatives 3 and 6 ) or of 3‐oxo‐butanoic and ‐pentanoic acid ( 16 and 23 ). The mechanism of the brominations is interpreted. The conversion of serine to enactiomcrically pure dioxanones 26–28 ( Scheme 4 ) is also discussed.