Tetrahedral Intermediates, Lecture notes of Chemistry

Download Tetrahedral Intermediates and more Lecture notes Chemistry in PDF only on Docsity!

t1/2 = minutes

chelate interaction stabilizes TS

2.06 A

E. Kwan Tetrahedral Intermediates Chem 106 Tetrahedral Intermediates Eugene E. Kwan October 29, 2014. OH rtowe Scope of Lecture specific vs. general acid-base catalysis alkaline vs. Weinreb acidic ester amides hydrolysis tetrahedral intermediates stereoelectronic effects concerted alcoholysis acetal hydrolysis and use as PGs Helpful References 1."Concerted Mechanisms of Acyl Group Transfer Reactions... Williams, A. Acc. Chem. Res. 1989, 22, 387-392. 2. "Mechanism and Catalysis for Hydrolysis of Acetals..." Cordes, E.H.; Bull, HG. Chem. Rev. 1974, 74, 581-603. 3. "Direct Observation of Simple Tetrahedral Intermediates." Capon. B.; Ghosh, A.K.; Grieve, D.M.A. Acc. Chem. Res. 1981, 14, 306-310. 4. "Tetrahedral Intermediates in the Reactions of Carboxylic Acid Derivatives with Nucleophiles." Adler, M; Adler, S.; Boche, G. J. Phys. Org. Chem. 2005, 18, 193-209. ; Key Questions What does isotopic exchange tell us about the mechanism | of this reaction? Me o* Me O* oe _3MH,SO, OH Me’ Me H,0 Me’ Me Could this occur by a concerted mechanism? 9 AL Me : O° : 4 — A ' ary + Aro ar Je + Ar'o® ' What's the rate-determining step here? RO OR H* Oo +240 == Jl + 2ROH ' ROR ROR Can tetrahedral intermediates be observed directly? CH3O H 86.17 dg-acetone/ CHO H 85.27 Oo ' ‘OCH D,0 _, ms fast OCH, slow H ‘OCH; ' Hgc~ So 88.22 high energy precursor Why does this reaction stall at 50% conversion? ' R ot gL ' LOM O-Me N 8 prosti — RoR/ — cy -R Me Cy Me ‘not appreciably 1.0 equiv complexed by Li lecture notes edited by Richard Liu