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X‐Ray Crystal Structures of the Enolate of tert ‐Butyl α‐Cyanoacetate with Li + or Protonated 1,8‐Diazabicyclo[5.4.0]undec‐7‐ene (DBU‐H + ) as Gegenion. N—H Hydrogen Bridge from DBU‐H + to the Enolate Oxygen Atom
Author(s) -
Boche Gernot,
Langlotz Ira,
Marsch Michael,
Harms Klaus
Publication year - 1994
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19941271031
Subject(s) - chemistry , protonation , crystal structure , alkali metal , crystallography , lithium (medication) , oxygen atom , medicinal chemistry , molecule , stereochemistry , ion , organic chemistry , medicine , endocrinology
For the first time a solid‐state structure with protonated 1,8‐diazobicyclo[5.4.0]undec‐7‐ene (DBU‐H + ) as the gegenion of an “organic” anion, namely tert ‐butyl α‐cyanoacetate ( 2 ‐ ), is determined. The DBU‐H + N—H bond forms a hydrogen bridge to the enolate oxygen atom of 2 ‐ , the first N‐H bridge to an enolate oxygen atom ever characterized. The structure of 2 ‐ DBU‐H + is compared with that of the corresponding lithium compound [ 2 ‐ Li + · TMEDA] 2 in which the cations are bound to the N atoms of the cyano groups and the enolate O atoms forming a twelve‐membered ring. Literature reports on the rather different chemistry of anions like 2 ‐ having alkali metal ions or DBU‐H + , respectively, as the gegenions can be understood by means of the two new solid‐state structures disclosed in this publication.