Stereoselective Addition of Grignard Reagents to New P-Chirogenic N-Phosphinoylbenzaldimines: Effect of the Phosphorus Substituents on the Stereoselectivity:

Several phosphinoylimines have been synthesized in five steps by starting from the appropriate phosphane oxide and were then treated with methylmagnesium bromide to give both diastereoisomers in high yields and with promising diastereomeric ratios. Then N‐[(tert‐butyl)(phenyl)phosphinoyl]benzaldimine, which displayed the best results, was subjected to the 1,2‐addition of various Grignard reagents to evaluate the best chiral induction due to the stereogenic phosphorus atom. The corresponding adducts were obtained in excellent yields and with moderate to excellent diastereoisomeric ratios

Complex Formation via Hydrogen bonding between Rhodamine B and Montmorillonite in Aqueous Solution

Abstract This study investigates the adsorption mechanism differences among four nitrogenous dyes, sulforhodamine G (SRG), uncharged/deprotonated rhodamine B (RhB), orange II (Or II) and methyl blue (MB) by montmorillonite (MMT). MMT adsorption capacity for cationic MB was three times that of uncharged RhB and anionic SRG, while anionic Or II was not absorbed. Colloidal MMT particles have two types of surfaces, basal and edge, that interact with nitrogenous dyes very differently. The surface acidity of MMT was characterized with the pyridine adsorption method using in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS). Adsorption of cationic MB was compared with the adsorption of RhB. In-situ attenuated total reflectance Fourier transform infrared (in-situ ATR-FTIR) spectroscopy indicated that a nitrogen atom on RhB complexes with a metal hydroxyl on an MMT edge through a water bridge. The highly polar edge hydroxyl is important to hydrogen bond formation. Cation ion exchange and washing experiments, as well as studies on the effect of temperature, pH and ionic strength on adsorption further clarified the adsorption mechanism. Our results provide insights into the effects of molecular structure on the adsorption of nitrogenous dyes by clay and the role of edge surfaces in the adsorption process

Synthesis of heterocyclic compounds via gold-catalysed enyne rearrangements

Syntheses of heterocycles using different gold-catalysed rearrangements of enynes are discussed in this chapter. The term skeletal rearrangement has been used in a broad sense to include reactions involving cyclopropyl gold carbene intermediates formed by initial enyne cyclisation, which can undergo many different transformations to give a wide range of heterocyclic structures. Other transformations involving rearrangement of propargylic esters and [3,3]-rearrangement (concerted or stepwise comprising metallic intermediates), as well as special cases, have also been covered. References to earlier work in this area and to recent reviews have been included, but the focus of the chapter is to present recent developments, interesting cases and an overview on how subtle differences in the enyne starting materials, the catalyst used or the reaction conditions can alter the reaction pathway increasing the structural diversity towards complex heterocyclic structures of high value