Resolution of the First Nonracemic Diquats

Abstract

Three tricyclic diquats with an eight-membered ring were prepared and shown to be the first configurationally stable derivatives of their kind. Resolution was achieved by using chiral hexacoordinated phosphorus BINPHAT and TRISPHAT anions. The diquat cations were obtained in high diastereo- and enantiomeric purity (ee>96% in most cases). X-ray diffraction analysis coupled with circular dichroism (CD) measurements allowed a precise determination of the relative and absolute configuration of the salts. The barriers to racemization of these compounds were calculated by using CD time-course measurements at different temperatures, affording DeltaG(++) values above 25 kcal mol(-1). Derivatives 4a, 4b, and 4c are the first eight-membered-ring derivatives with only three ring constraints to be resolved. This manuscript also reports the first procedure to remove TRISPHAT anions after diastereomeric separation.

Ferrocenyl Diquat Derivatives: Nonlinear Optical Activity, Multiple Redox States, and Unusual Reactivity

“…In addition, the UV–vis spectrum (Figure S4) lacks an intense, low-energy MLCT band characteristic of the conjugated chromophores 1 – 4 . Unlike recently reported nonracemic diquats containing eight-membered rings, [ 4b ] 4+ appears to be conformationally flexible at room temperature.…”

Diquats with Robust Chirality: Facile Resolution, Synthesis of Chiral Dyes, and Application as Selectors in Chiral Analysis

“…More recently, the Lacour group revisited some of these dications (Scheme b), and reported the resolution and determination of racemization barriers. This elegant study found the barriers of the selected example diquats to be relatively low (Δ G ≠ =106–112 kJ mol −1 at 20 °C) …”

“…[7] However,t he configurational stability and resolution of the enantiomers were not addressed in theser eports.M ore recently,t he Lacour groupr evisiteds omeo ft hese dications (Scheme 1b), and reportedt he resolution and determination of racemization barriers. [8,9] Non-racemic diquats with comfortably high barriers preventing thermalr acemization even at 150-200 8Cw ill enable av ariety of application studies without being restricted to low temperatures. [8,9] Non-racemic diquats with comfortably high barriers preventing thermalr acemization even at 150-200 8Cw ill enable av ariety of application studies without being restricted to low temperatures.…”

“…This elegant study found the barriers of the selected example diquats to be relativelyl ow (DG ¼ 6 = 106-112 kJ mol À1 at 20 8C). [8,9] Non-racemic diquats with comfortably high barriers preventing thermalr acemization even at 150-200 8Cw ill enable av ariety of application studies without being restricted to low temperatures. Such configurational stability would be comparable to that of axially chiral binaphthyls,w hichh ave been widely applied.…”

Configurationally Stable Doubly Bridged Biphenyl Azocines through Copper-Catalyzed Double Carbene Insertions into the Corresponding Azepines

“…This ambivalent behavior is conceptually interesting and can be used for the development of stereodivergent pathways and subsequent applications. 5,14 Knowing, in ortho-ortho′-bridged biaryls, that eight-membered-ring derivatives are usually more configurationally stable that seven-membered analogues, 15 and that this trend is reinforced by a double tethering, 16 an approach was developed for the construction of doubly bridged biphenyl azocines of type 4 and 5 (Figure 1, bottom). Herein, these derivatives S. Harthong et al…”