Dual activation in asymmetric allylsilane addition to chiral N-acylhydrazones: method development, mechanistic studies, and elaboration of homoallylic amine adducts.
[reaction: see text] Chiral N-acylhydrazones derived from commercially available 4-benzyl-2-oxazolidinone provide a rigid, conformationally restricted template to impart facial selectivity in additions to C=N bonds. In the presence of indium(III) trifluoromethanesulfonate [In(OTf)3], N-acylhydrazones undergo highly diastereoselective fluoride-initiated additions of allylsilanes (aza-Sakurai reaction). Mechanistic studies including control experiments and comparisons with allyltributylstannane, allylmagnesium bromide, and allylindium species implicate a dual activation mechanism involving addition of an allylfluorosilicate species to a chelate formed from In(OTf)3 and the chiral N-acylhydrazone. The N-N bonds of the adducts are readily cleaved in a two-step protocol to provide synthetically useful homoallylic N-trifluoroacetamides. Further elaboration of the latter compounds through Wacker oxidation and olefin metathesis provides diversely functionalized building blocks and expands the potential applications of this C-C bond construction approach to asymmetric amine synthesis.
Friestad
Gregory K
GK
Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, USA. gregory-friestad@uiowa.edu
Korapala
Chandra Sekhar
CS
Ding
Hui
H
D000081:Acetamides; D000215:Acylation; D000447:Aldehydes / Q000737:chemistry; D000475:Alkenes / Q000737:chemistry*; D000588:Amines / Q000737:chemistry*; D004583:Electrons; D005463:Fluoroacetates; D006835:Hydrazones / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D012821:Silanes / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry; D013237:Stereoisomerism; D014269:Trifluoroacetic Acid / Q000737:chemistry
D000081:Acetamides; D000447:Aldehydes; D000475:Alkenes; D000588:Amines; D005463:Fluoroacetates; D006835:Hydrazones; D007659:Ketones; D012821:Silanes; C511847:allylsilane; C030688:trifluoroacetamide; D014269:Trifluoroacetic Acid; D009584:Nitrogen; D012825:Silicon