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Studien zur enantio‐ und diastereoselektiven α‐Metallierung prochiraler Sulfoxide mit (+)‐Menthyllithium
Author(s) -
Maercker Adalbert,
Schuhmacher Rudolf,
Buchmeier Willi,
Lutz Heinz Dieter
Publication year - 1991
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.19911241120
Subject(s) - chemistry , racemization , diastereomer , transmetalation , sulfoxide , deprotonation , medicinal chemistry , benzophenone , acetophenone , enantiomer , stereochemistry , methylene , ether , organic chemistry , catalysis , ion
Enantio‐ and Diastereoselective α‐Metallation of Prochiral Sulfoxides by (+)‐Menthyllithium 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 40%. Dicyclohexyl sulfoxide ( 3c ) was deprotonated enantioselectively with an e.e. of 30%. 2‐Bornyllithium ( 21 ) was unsuccessful as a chiral base and was shown for the first time to contain 4% of isobornyllithium ( 22 ). The reactions were performed in pentane at – 80°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.