10.1021/ja011337j
This study comprehensively investigates the stereoselectivity of Lewis acid-promoted aldol reactions involving achiral enol silanes and chiral α-hydroxyaldehydes under chelation-controlled conditions. The main objective was to evaluate the chelating effect of dimethylaluminum chloride (Me2AlCl) and methylaluminum dichloride (MeAlCl2) in carbonyl addition reactions. The experiments involved the use of various Lewis acids including TiCl4, SnCl4, Me2AlCl, and MeAlCl2, as well as substrates such as α-alkoxy and α-siloxy aldehydes. The reactions were analyzed using gas chromatography (GLC), nuclear magnetic resonance (NMR) spectroscopy, and semi-empirical calculations (PM3) to determine the diastereoselectivity and the influence of the R and α-stereocenters on the stereochemical outcome. The studies demonstrated that Me2AlCl and MeAlCl2 exhibited excellent chelating abilities even in the presence of hindered substrates, leading to high levels of selectivity in the formation of both cis- and trans-diastereoisomers.
10.1021/om00135a016
The research focuses on the synthesis and characterization of organometallic compounds, specifically metallacycles and titanium-carbene complexes. The purpose of the study was to prepare a titanacyclobutane precursor, which was then reacted with benzophenone to yield an organic product, and further reacted with phosphines to obtain phosphine adducts of an α-substituted titanium-carbene complex. The researchers also succeeded in creating a heterobimetallic alkylidene complex by reacting the metallacycle with dimethylaluminum chloride. The conclusions drawn from the study indicate that the observed reactivity of the metallacycle is consistent with productive cleavage of the metal-containing ring, leading to the formation of titanium-carbene complexes. The chemicals used in the process include 3,3-dimethylcyclopropene, Tebbe reagent, (dimethylamino)pyridine (DMAP), benzophenone, phosphines (PMeR2, where R = Me, Ph), and dimethylaluminum chloride, among others. The study provides insights into the reactivity of metallacycles and their potential as precursors to titanium-carbene compounds.
10.1016/S0040-4039(00)85086-8
The research investigates the thermal and Lewis acid catalyzed intramolecular Diels-Alder reactions of dienes (compound 1, where n = 5-11) to form 7-11 membered rings, with a focus on the stereoselectivity and feasibility of these reactions. The study aimed to understand the influence of different reaction conditions on the formation of medium-sized rings, which are challenging to synthesize through other means. The researchers found that catalyzed reactions efficiently formed larger rings and predominantly produced cis adducts, while Lewis acids prevented the formation of five-membered rings. The chemicals used in the process included dienes with varying chain lengths, Lewis acids such as Me2AlCl, and solvents like benzene and toluene. The study concluded that the feasibility and stereoselectivity of these reactions are of significant importance for the synthesis of medium ring systems in natural products chemistry.
