42447-90-5Relevant articles and documents
Reactions of an Allylic Carbocation with Nucleophiles in Aqueous Solvents
Thibblin, Alf
, p. 313 - 320 (2007/10/02)
The allylic carbocation formed from 3-(2-X-propan-2-yl)indene (1-X) (X = Cl, OAc, or OH2+), or from 2-acetoxy-1-isopropylideneindan (2-OAc) in aqueous solvents containing ca. 75 vol percent water reacts rapidly with nucleophiles.The selectivity is very low: βnuc ca. 0.07 with alcohols as nucleophiles and βnuc ca. 0.03 with substituted acetate anions.The nucleophile attacks at both ends of the allylic system but preferentially at the exocyclic carbon atom, giving the thermodynamically more stable product.Azide anion reacts with the carbocation about 50 times as fast as does water.The solvolysis of the allylic isomers (1-OAc) and (2-OAc) is accompanied by intramolecular rearrangement of the acetates as well as hydron abstraction by the leaving acetate anion, yielding the 1,2- and 1,4-elimination products.The elimination product compositions are quite different, which indicates two discrete ion-pair intermediates.It is concluded also that the isomerization proceeds by an ion-pair route, since in less polar solvents it has only been observed along with solvolysis and elimination.The experimental results for the acetates accomodate well a mechanism in which solvolysis, rearrangement, and elimination are connected via two contact ion-pair intermediates.
Enlarged Deuterium Isotope Effects in Oxyanion-Catalyzad 1,3 Proton Transfer Competing with 1,2 Elimination as a Probe of a Common Tightly Hydrogen-Bonded Intermediate
Thibblin, Alf
, p. 853 - 858 (2007/10/02)
The reaction of 1-(2-acetoxy-2-propyl)indene (1-h) or 1-(2-acetoxy-2-propyl)indene (1-d) with p-NO2PhO- in methanol buffered with p-NO2PhOH results in base-catalyzed 1,3 proton transfer, yielding 3-(2-acetoxy-2-propyl)indene (2-h) and 3-(2-acetoxy-2-propyl)indene (2-d), respectively, in competition with base-promoted 1,2-elimination producing 1-isopropylideneindene (3-h) and 1-isopropylideneindene (3-d), respectively.The overall deuterium isotope effect on the reaction of 1 was measured as (k12H + k13H)/(k12D + k13D) = 5.2, which is composed of the rearrangement isotope effect k12H/k12D = 12.2 +/- 1.0 and the elimination isotope effect k13H/k13D = 3.6.The enlarged rearrangement isotope effect shows that the intramolecularity of the 1,3 proton-transfer reaction is substantial.The intramolecularity was determined as ca. 87percent for = 0.24 M and ca. 80percent for = 0.71 M by analyzing the 2H content of the product 2-d.The amplified isotope effect on the 1,3-prototropic shift together with the attenuated elimination isotope effect shows that the two reactions are coupled via at least one common intermediate, which is concluded to be a tightly hydrogen-bonded complex between the protonated base and the carbanion.An increase in basicity of the oxyanion favors elimination at the expense of rearrangement.Reaction of 2-h and 2-d predominantly give 1,4 elimination accompanied by a trace of competing 1,3 proton transfer.The isotope effect k23H/k23D was measured to 2.5; it is small owing to a large amount of internal return.
