3294-50-6Relevant academic research and scientific papers
Enantio- and Diastereoselective α-Metallation of Prochiral Sulfoxides by (+)-Menthyllithium
Maercker, Adalbert,Schuhmacher, Rudolf,Buchmeier, Willi,Lutz, Heinz Dieter
, p. 2489 - 2498 (2007/10/02)
Six out of ten prochiral dialkyl sulfoxides 3 with diastereotopic α methylene protons were stereoselectively metallated by (+)-menthyllithium (11) to yield two diastereomeric pairs of enriched enantiomers 29 after the reaction with benzophenone.The maximum e.e. was 40percent.Dicyclohexyl sulfoxide (3c) was deprotonated enantioselectively with an e.e of 30percent. 2-Bornyllithium (21) was unsuccesful as a chiral base and was shown for the first time to contain 4percent of isobornyllithium (22).The reactions were performed in pentane at -80 deg C; in diethyl ether and THF the e.e's were only slightly higher, and at higher temperatures the selectivity was rapidly decreasing.It was shown that racemization takes place by an intermolecular transmetallation reaction.The structure of 29f (n = 3) was elucidated by an X-ray analysis.Key Words: (+)-Menthyllithium, stereoselective metallation with/ Prochiral sulfoxides, enantio- and diastereoselective α-deprotonation of / 2-Bornyllithium, content of isobornyllithium in / Racemization, mechanism by intermolecular transmetallation/ e.e., temperature dependence of
