Toward the development of a structurally novel class of chiral auxiliaries. Conformational properties of the aldol adducts of oxadiazinones: observation of unusual shielding effects.
Asymmetric aldol reactions were conducted with the titanium enolate of N(3)-hydrocinnamoyl-3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one to afford aldol adducts 5a-j. The dominant product of the asymmetric aldol reaction was the non-Evans syn adduct as determined by (1)H NMR spectroscopy and X-ray crystallography. When evaluating the (1)H NMR spectra of adducts 5a-j, a highly shielded signal with an average chemical shift of 0.05 ppm was observed. This signal was readily determined to be the C(5)-methyl group of the oxadiazinone. It is presumed that the overall conformation adopted by the aldol adducts in solution places an aromatic ring of the N(3)-substituent in close proximity to the C(5)-methyl group. An investigation of this conformational preference is conducted employing (1)H NMR spectroscopy, X-ray crystallography, and computational methods.
Burgeson
James R
JR
Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, USA.
Renner
Matthew K
MK
Hardt
Ingo
I
Ferrence
Gregory M
GM
Standard
Jean M
JM
Hitchcock
Shawn R
SR
D000447:Aldehydes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D010069:Oxadiazoles / Q000737:chemistry*; D019258:Saquinavir / Q000737:chemistry; D013237:Stereoisomerism; D013816:Thermodynamics
D000447:Aldehydes; D010069:Oxadiazoles; D019258:Saquinavir