C(2) Enolate: Enolate or Enamine?

Pyrrolidin-3-ones enolise away from the ring nitrogen.1 Attempts to improve the C(2):C(4) enolate ratio only managed to equal the product ratios obtained previously.1


Experimental Conditions C(2) : C(4)

enolate(2) enolate(3) LDA, TESCl, THF, -78 °C 1 : 1.3 LDA, TESCl, THF, -78 °C in situ 1 : >8 electrophile LDA, TESCl, THF, -78 °C reverse 1 : >7 addition nBuLi, HN(C6H10)2, -78 °C 1 : 1.7 LTMP, TESCl, THF, -78 °C 1 : 3.5 Garst et al(ref1): LDA, TESCl THF, -78 °C 1 : 1
Regioisomeric composition calculated from the 1H NMR of the silyl enol ethers.

LTMP=lithium tetramethyl-piperidide,

Preference for the C(4) enolate in the pyrrolidin-3-one can be attributed to steric interaction between hydrogens in the C(2) enolate conformation.

To study the C(2) enolate and its reactions in greater detail the 4,4'- dimethyl-pyrrolidinone(9) has been synthesised.

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