Enantioselective formation of tert-alkylamines by desymmetrization of 2-substituted serinols.
Novel enantioselective desymmetrization of 2-substituted 2-amino-1,3-propanediols has been established to generate asymmetric quaternary carbon centers comprising an amino group. Enantioselective as well as chemical conversion proved to be greatly dependent on the protecting group of the amino group in the substrate, desymmetrizing reagent, base, solvent, and naturally, catalyst. The highly effective desymmetrization has been implemented by using N-benzoylated substrates with benzoyl chloride and triethylamine in the presence of tetraphenylbisoxazoline (24)-CuCl(2) complex in THF at ambient temperature. An extensive survey of catalysts revealed that dimethylmalonate-bridged bisoxazoline-CuCl(2) complexes were superior. Among them, the tetraphenylbisoxazoline (24)-CuCl(2) complex turned out to work most efficiently with a wide array of the substrates. All the examined substrates, with the exception of 2-phenylserinol 36, were desymmetrized in the presence of 24-CuCl(2) complex to give high enantioselectivities ranging from 85 to 95 % ee. Complementary use of the diisopropylbisoxazoline (22)-CuCl(2) complex has remedied the mediocre desymmetrization of 36 to give a significantly improved enantioselectivity from 63 to 83 % ee.
Hong
Mi Sook
MS
Center for Molecular Design and Synthesis, Department of Chemistry, School of Molecular Science (BK21), KAIST, Daejeon, Korea.
Kim
Tae Woo
TW
Jung
Byunghyuck
B
Kang
Sung Ho
SH
D000588:Amines / Q000138:chemical synthesis*; D009682:Magnetic Resonance Spectroscopy; D011412:Propanolamines; D011409:Propylene Glycols / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism
D000588:Amines; D011412:Propanolamines; D011409:Propylene Glycols; C072422:serinol