title: Absolute asymmetric synthesis of enantiopure organozinc reagents, followed by highly enantioselective chlorination.
abstract: We report the absolute asymmetric synthesis (AAS) of indenylzinc reagents by using total spontaneous resolution followed by enantiospecific conversion into 1-chloroindene. The chiral complex [Zn(dcp)(ind)(tmeda)] (dcp = 2,6-dichlorophenoxy and tmeda = N,N,N',N'-tetramethylethylenediamine) (3) was prepared from the achiral starting materials indene, potassium, zinc chloride, TMEDA, and 2,6-dichlorophenol. The reagent resolved spontaneously on crystallization, and single crystals of 3 react with N-chlorosuccinimide in the presence of benzoquinone in 2-propanol to give 1-chloroindene in >98 % enantiomeric excess. It was found that (R)-3 gave (R)-1-chloroindene upon reaction, indicating an SE 2'-mechanism. Since bulk samples of 3 gave optically active product upon chlorination, total spontaneous resolution must have occurred. This demonstrates that enantiopure products can be obtained through the absolute asymmetric synthesis of organometallic reagents starting from achiral materials. The general absolute asymmetric synthesis (AAS) method offers easy access to both enantiomers and an almost limitless variation in the design of the product.
authors.affiliation: Department of Chemistry and Molecular Biology, University of Gothenburg, 412 96 Gothenburg (Sweden).
authors.forename: Susanne
authors.initials: S
authors.lastname: Olsson
authors.forename: Anders
authors.initials: A
authors.lastname: Lennartson
authors.forename: Mikael
authors.initials: M
authors.lastname: Håkansson
keywords: asymmetric synthesis; chirality; crystal growth; enantioselectivity; total spontaneous resolution; zinc