The use of (–)-sparteine/organolithium reagents for the enantioselective lithiation of 7,8-dipropyltetrathia[7]helicene: single and double kinetic resolution procedures

Doulcet, Julien and Stephenson, G. Richard (2015) The use of (–)-sparteine/organolithium reagents for the enantioselective lithiation of 7,8-dipropyltetrathia[7]helicene: single and double kinetic resolution procedures. Chemistry - A European Journal, 21 (51). pp. 18677-18689. ISSN 0947-6539

Full text not available from this repository. (Request a copy)

Abstract

The effect of organolithium reagent (RLi: R = n-Bu, i-Pr, s-Bu, t-Bu), solvent (diethyl ether, diethyl ether/THF and MTBE), and stoichiometry on the (–)-sparteine-mediated silylation of 7,8-dipropyltetrathia[7]helicene shows that, unusually, substantially more than 0.5 eq of RLi (R = i-Pr, s-Bu, t-Bu) and a large excess of (–)-sparteine (R = n-Bu, s-Bu) is often needed to achieve substantial conversions and good e.e.s. With n-BuLi, however, just 1 equivalent of the organolithium reagent is sufficient. Our best results were obtained using the convenient t-BuLi/(–)-sparteine adduct with which the need for a high (–)-sparteine:RLi ratio can be avoided. Single- and double-KR procedures give enantiopure samples of 2-trimethylsilyl- and 2,13-di(trimethylsilyl)-7,8-dipropyltetrathia-[7]helicene and two-step double-KR combining (–)-sparteine/s-BuLi and chiral formamides affords the synthetically valuable 2-formyl-7,8-dipropyltetrathia[7]helicene. This is the first use of (–)-sparteine for the enantioselective lithiation of helicenes and the first report of t-BuLi outperforming s-BuLi in a (–)-sparteine-mediated procedure.

Item Type: Article
Uncontrolled Keywords: tetrathia[7]helicenes,asymmetric synthesis,(–)-sparteine-mediated lithiation ,kinetic resolution ,double-kr
Faculty \ School: Faculty of Science > School of Chemistry
University of East Anglia > Faculty of Science > Research Groups > Synthetic Chemistry
Depositing User: Pure Connector
Date Deposited: 13 Jan 2016 10:01
Last Modified: 25 Jul 2018 11:14
URI: https://ueaeprints.uea.ac.uk/id/eprint/56277
DOI: 10.1002/chem.201502958

Actions (login required)

View Item