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Chiral Organometallic Reagents, IX. On the Origins of the Diastereoselectivity in the Bromine/Lithium Exchange of 3–Alkoxy–1,1–dibromoalkanes
Author(s) -
Hoffmann Reinhard W.,
Brumm Karen,
Bewersdorf Martin,
Mikolaiski Wolfgang,
Kusche Andreas
Publication year - 1992
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.19921251220
Subject(s) - chemistry , substituent , conformational isomerism , alkoxy group , bromine , butyllithium , reagent , derivative (finance) , stereochemistry , medicinal chemistry , lithium (medication) , alkyl , organic chemistry , molecule , economics , medicine , financial economics , endocrinology
The 3–alkoxy–1,1–dibromopentanes 5 are compounds, which according to MM2 calculations populate one conformation to >80% at −110°C. On reaction with n ‐butyllithium the bromine atom which resides in the extended position is exchanged with selectivities around 80:20, irrespective of the nature of the oxy residue at C–3. The role of this substituent is solely to bias the conformational equilibria in favor of the conformer 17 . Coordination of the butyllithium to the oxygen functionality plays an important role only in the carbamoyl derivative 5f , for which the sense of the asymmetric induction is reversed.