Configurational Stability of Oxymethyllithiums as Intermediates in Intramolecular Rearrangements
作者:Dagmar C. Kapeller、Lothar Brecker、Friedrich Hammerschmidt
DOI:10.1002/chem.200701054
日期:2007.11.26
were tested for their microscopic configurational stability in intramolecular isomerizations, such as the silyl- and germyl-[1,2]-retro-Brook and the sigmatropic[2,3]-Wittig rearrangement. The influence of temperature, solvent, and migrating group on the stability of the intermediate carbanions was studied. Furthermore, the stereochemical course of these rearrangements was elucidated, resulting in highly
Formal and improved synthesis of enantiopure chiral methanol
作者:Anna Schweifer、Friedrich Hammerschmidt
DOI:10.1016/j.tet.2008.05.091
日期:2008.8
[D2]Methanol was converted to the carbamate derived from 2,2,6,6-tetramethylpiperidine. It was metalated with s-BuLi/TMEDA at -78 C with a high primary kinetic isotope effect to give an n.-oxymethyllithium, which was silylated with chlorodimethylphenylsilane. The silylmethyl carbamate formed was lithiated and borylated with the borate derived from tert-butanol and (R,R)-1,2-dicyclohexylethane-7,2-diol to give diastereomeric boronates, which were separated by preparative HPLC and can in principle be converted to enantiopure chiral methanols. Thus, both enantiomers are easily accessible in nine linear steps. (C) 2008 Elsevier Ltd. All rights reserved.