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Stereoselektive Protonierung von Carbanionen, 1. Diastereoselektive Protonierung von C – H‐aktivierten Cyclohexan‐Derivaten
Author(s) -
Gerlach Uwe,
Haubenreich Thomas,
Hünig Siegfried,
Keita Yango
Publication year - 1993
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.19931260522
Subject(s) - chemistry , protonation , deprotonation , carbanion , diastereomer , cyclohexanes , lewis acids and bases , medicinal chemistry , base (topology) , proton , stereochemistry , alkylation , organic chemistry , catalysis , ion , mathematical analysis , physics , mathematics , quantum mechanics
The diastereoselectivity of the kinetically controlled protonation of carbanions derived from 4‐ tert 1‐butyl‐1‐X‐cyclohexanes ( 1 : XCN, 2 : XCO 2 Me, 2‐Si : XC(OMe)OSiMe 3 , 3 : XCOPh, 4 : XSO 2 Ph) is systematically investigated. By variation of (a) the base for deprotonation of 1 – 4 , (b) OH‐, NH‐, and CH‐proton sources, (c) added salts, Lewis bases, and acids, (d) solvents (cf. Tables 2 – 5) the cis/trans ratios of diastereomers could be influenced as follows: 1 : 41/59→85/15; 2 : 26/74→73/27; 3 : 26/74→>93/<3; 4 : 1/99→37/63. The results are discussed with regard to structure and aggregation of 1 Li to 4 Li and compared with relevant data from the literature. It is concluded that so far an empirical approach to high diastereoselectivities cannot be avoided and that the results cannot be predicted from the ratios obtained by the much slower alkylation reactions.