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Formation of Isomeric BAr 3 Adducts of 2‐Lithio‐ N ‐methylimidazole
Author(s) -
Vagedes Dominik,
Kehr Gerald,
König Dagmar,
Wedeking Katrin,
Fröhlich Roland,
Erker Gerhard,
MückLichtenfeld Christian,
Grimme Stefan
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200208)2002:8<2015::aid-ejic2015>3.0.co;2-8
Subject(s) - chemistry , deprotonation , carbene , methyllithium , adduct , intramolecular force , medicinal chemistry , imidazole , lewis acids and bases , nucleophile , transmetalation , stereochemistry , ion , organic chemistry , catalysis
N ‐Methylimidazole added to the strong organometallic Lewis acid B(C 6 F 5 ) 3 at the donor nitrogen atom to form the adduct 3 (characterized by X‐ray diffraction). Deprotonation at the imidazole carbon atom C‐2 was achieved by treatment with methyllithium to generate the reactive “Arduengo carbene anion” intermediate 4 , which underwent a rapid subsequent intramolecular nucleophilic aromatic substitution reaction at one of the adjacent C 6 F 5 groups to form the tricyclic betaine‐type product 5 . Rearrangement of 4 by 1,2‐boron migration was not observed. The respective isomer 7 was prepared independently by deprotonation of N ‐methylimidazole, followed by C‐2 addition of B(C 6 F 5 ) 3 . The corresponding N ‐methylimidazolide‐2−B(C 6 H 5 ) 3 adduct 8 was characterized by X‐ray diffraction and shown to have a cyclodimeric structure made up of intermolecular bis(π‐arene)(imidazole)lithium units. A DFT study revealed that the N ‐borated Arduengo carbene anions are in general very effectively kinetically protected from undergoing intramolecular rearrangement to their thermodynamically favored 2‐boratoimidazole anion isomers by 1,2‐BR 3 migration. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)