Date of Award
Fall 1981
Project Type
Dissertation
Program or Major
Chemistry
Degree Name
Doctor of Philosophy
Abstract
A chiral aminotriol, tris-{(S)-2-hydroxypropyl}amine (1) was synthesized from ammonia and three equivalents of (S)-propylene oxide. The triol was allowed to condense with boric acid to form a bicyclic borate {(S,S,S)-triisopropanolamine borate, 2} which was allowed to react with a suspension of potassium hydride in tetrahydrofuran to form a borate hydride {potassium (S,S,S)-triisopropanolamine borate hydride, 3}. Propiophenone was reduced to optically active alcohol in 14% enantiomeric excess (ee) (R) by 3 in THF.
By reaction of n-butylamine, t-butylamine and (R)-and (S)-1-phenylethylamine with two equivalents of (S)-propylene oxide or ethylene oxide five chiral aminodiols were prepared: N-n-butyl-bis-{(S)-2-hydroxypropyl}amine (4), N-{(R)-1-phenylethyl}-bis-(2-hydroxyethyl)amine (5), N-{(R)-1-phenylethyl}-bis-{(S)-2-hydroxypropyl}amine (6), N-{(S)-1-phenylethyl}-bis-{(S)-2-hydroxypropyl}amine (7) and N-{tert-butyl}-bis-{(S)-2-hydroxypropyl}amine (8).
The aminodiols were added to ethereal lithium aluminum hydride (LAH) to produce chiral, modified LAH reagents which were used to reduce prochiral ketones. The modified LAH reagents from ligands 4, 5, 6 and 7 quantitatively reduced acetophenone {44%ee(R), 10%ee(S), 35%ee(R) and 82%ee(R), respectively} and propiophenone {57%ee(R), 10%ee(S), 19%ee(R) and 77%ee(R), respectively}. A general additivity of asymmetric induction due to the chiral centers in the carbinol and noncarbinol arms of the ligands was perceived, with 7 optimizing the inductive influences. The direction of the asymmetric induction was rationalized by means of a stereocorrelation model in which the ketone is coordinated with a lithium cation that is simultaneously coordinated with the nitrogen and two oxygens of the aminodiol ligand (in the form of a dialkoxydihydriodoaluminate).
Unique and unpredictable behavior was observed with the LAH reagent from 8. The enantiomeric composition was observed to vary wildly {83%ee(R) to 32%ee(S)} in roughly comparable reductions of propiophenone. This strange behavior has not been fully rationalized.
Recommended Citation
GRANDBOIS, EDWARD ROLAND, "ASYMMETRIC REDUCTIONS BY CHIRAL LITHIUM-ALUMINUM HYDRIDE AND POTASSIUM-BOROHYDRIDE REAGENTS" (1981). Doctoral Dissertations. 1305.
https://scholars.unh.edu/dissertation/1305