Ion-pair intermediates and extreme deuterium isotope effects in partially diastereospecific base-promoted elimination competing with base-catalyzed 1,3-proton transfer

Journal Article · Wed Nov 21 04:00:00 EST 1979 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00518a029· OSTI ID:5738310

Thibblin, A; Ahlberg, P

Reaction of threo- or erythro-1-(1-acetoxyethyl)indene (1-h and 2-h) with quinuclidine (Q) or sodium methoxide (NaOMe) in methanol results in base-promoted 1,2 elimination to give a mixture of (E)- and (Z)-1-ethylidenindene (4a-h and 4b-h). In the reactions with Q, base-catalyzed 1,3-proton transfer producing 3-(1-acetoxyethyl)indene (3-h) competes with the eliminations. The latter compound undergoes base-promoted 1,4 elimination also yielding a mixture of 4a-h and 4b-h. The corresponding 1,3-dideuterated compounds 1-d and 2-d and the 1,1-dideuterated compound 3-d yield, within experimental error, the same ratio of the elimination products (E)- and (Z)-(3-/sup 2/H)-1-ethylidenindene (4a-d and 4b-d) as the protium analogues. With NaOMe, the kinetic isotope effects are k/sup H//sub 14//k/sup D//sub 14/ = 6.6 + 1.8 or -1.4, k/sup H//sub 24//k/sup D//sub 24/ = 6.9 +- 0.3, and k/sup H//sub 34//k/sup D//sub 34/ = 7.5 +- 1.1, respectively. The isotope effects measured with Q are (k/sup H//sub 13/ + k/sup H//sub 14/)/(k/sup D//sub 13/ + k/sup D//sub 14/) = 7.1 +- 0.3 and (k/sup H//sub 23/ + k/sup H//sub 24/)/(k/sup D//sub 23/ + k/sup D//sub 24/) = 7.3 + 1.6 or -1.2, respectively. The isotope effect on the 1,4-elimination reaction of 3 with Q is k/sup H//sub 34//k/sup D//sub 34/ = 3.5 +- 0.1 and no incorporation of protium in 4a-d and 4b-d was observed. This indicates that the reaction proceeds via partially reversibly formed ion pairs. The ion pair and tightly solvated carbanion elimination reactions are partially diastereospecific. The elimination mechanisms of the intermediates and the relationship between deuterium isotope effects and elimination reactions in general are discussed. 3 figures, 4 tables.

• Research Organization: Univ. of Uppsala, Sweden
• OSTI ID: 5738310
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 101:24; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
ALCOHOLS
ALKALI METAL COMPOUNDS
BASES
CATALYSIS
CHARGED-PARTICLE TRANSPORT
CHEMICAL REACTIONS
DEUTERIUM
HYDROGEN ISOTOPES
HYDROXY COMPOUNDS
ION PAIRS
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
METHANOL
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PROTON TRANSPORT
RADIATION TRANSPORT
SODIUM COMPOUNDS
STABLE ISOTOPES
STEREOCHEMISTRY