Efficient protocols for three-component catalytic enantioselective vinylogous Mannich (VM) reactions of alkyl-substituted aldimines (including those bearing heteroatom-containing substituents) and readily available siloxyfurans are presented. High efficiency and stereoselectivity is achieved through the use of o-thiomethyl-p-methoxyaniline-derived aldimines. Reactions, performed under an atmosphere of air and in undistilled THF, can be promoted in the presence of as little as 1 mol % of easily accessible amino acid-based chiral ligands and commercially available AgOAc. The desired products are obtained in 44% to 92% yield, and in up to >98:<2 diastereomer and >99:<1 enantiomer ratio (>98% ee). Removal of the N-activating group is performed through a one-vessel oxidation/ hydrolysis operation, which proceeds via a stable aza-quinone (characterized by X-ray crystallography). Evidence is presented indicating that reactions with chiral non-racemic aldehydes are subject to catalyst control: both substrate enantiomers react to afford the desired product diastereomers in high stereoselectivity. Aryl-and alkynyl-substituted o-thiomethyl-pmethoxyaniline-derived aldimines undergo Ag-catalyzed enantioselective VM more efficiently and with higher selectivity than the corresponding o-anisidyl substrates. Additionally, Ag-catalyzed azaDiels-Alder reactions of the alkyl-substituted aldimines bearing the structurally modified N-aryl unit afford enantiomerically enriched (up to 95% ee) products in up to 88% yield.

The case of the notorious aryls is solved: The first efficient catalytic and enantioselective method for allylic substitutions that furnish quaternary carbon stereogenic centers by additions of aryl‐ or heteroarylmetals is reported (see scheme). Highly site‐ and enantioselective processes begin with readily available organolithium reagents.

Jetzt auch mit Aryl: Die erste effiziente katalytische und enantioselektive Methode für allylische Substitutionen, die quartäre stereogene Kohlenstoffzentren durch Addition von Aryl‐ oder Heteroarylmetallen erzeugen, wird beschrieben (siehe Schema). Die hoch orts‐ und enantioselektiven Prozesse gehen von leicht verfügbaren Organolithiumreagentien aus.

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This study aimed to manipulate the texture and elemental composition of the novel sheaths produced by the iron-oxidizing bacterium Leptothrix in culture by altering components of the medium. When previously isolated strain OUMS1 was cultured in media (pH 7.0 throughout incubation) containing various levels of Si on a rotary shaker at 20 °C and 70 rpm for 14 days, the strain was able to reproduce in media with up to 300 ppm Si, and the hollow microtubular architecture of the sheath was maintained even at 300 ppm Si. The constitutional iron oxide phase changed from poorly crystalline lepidocrocite at 0 ppm Si to X-ray diffraction (XRD)-amorphous 2-line ferrihydrite at 100-300 ppm via their mixture phase with intermediate Si content . The results strongly indicate that the chemical character and crystallinity of the sheath texture can be regulated by culture conditions, especially components of the medium.