title: Stereoselective Synthesis and Retentive Trapping of α-Chiral Secondary Alkyllithiums Leading to Stereodefined α,β-Dimethyl Carboxylic Esters.
abstract: The treatment of α-chiral secondary alkyl iodides with tBuLi at -100 °C leads to the corresponding secondary alkyllithiums with high retention of configuration. Subsequent quenching with various electrophiles such as Bu2 S2 , DMF, MeOB(OR)2 , or Et2 CO provides the desired products with retention of configuration. Furthermore, a transmetalation with CuBr⋅P(OEt)3 also allows retentive trapping with acid chlorides and ethylene oxide. The quenching of the resulting alkyllithiums with ClCO2 Et furnishes stereoselectively syn- and anti-ethyl-2,3-dimethyl ester carboxylates (d.r.>94 %). Related esters bearing three adjacent stereo-controlled centers (stereotriads) have also been prepared. This method has been applied to the synthesis of the ant pheromone (±)-lasiol in 26 % overall yield (four steps) with d.r.=97:3 starting from commercially available cis-2,3-epoxybutane.
authors.affiliation: Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13, 81377, München, Germany.
authors.forename: Varvara
authors.initials: V
authors.lastname: Morozova
authors.affiliation: Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13, 81377, München, Germany.
authors.forename: Kohei
authors.initials: K
authors.lastname: Moriya
authors.affiliation: Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13, 81377, München, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Mayer
authors.affiliation: Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13, 81377, München, Germany. Paul.Knochel@cup.uni-muenchen.de.
authors.forename: Paul
authors.initials: P
authors.lastname: Knochel
keywords: carboxylic acids; copper; lithium; pheromone; stereotriads