Configuration-Dependent Medium-Sized Ring Formation: Chiral Molecular Framework with Three-Dimensional Architecture

This report describes a configuration-dependent [6 + 8 + 5] fused ring formation via a tandem cyclic N-acyliminium nucleophilic addition reaction. Cyclization of the acyclic precursor prepared on a solid phase using l-Ser and a racemic mixture of Fmoc-trans-2-aminocyclohexanecarboxylic acid predominantly yielded the cyclic diastereomer with the (1R,2R)-2-aminocyclohexane moiety rather than the tricyclic diastereomer from the (1S,2S)-enantiomer. In contrast, the model compound prepared with d-Ser predominantly cyclized with the (1S,2S)-2-aminocyclohexanecarboxylic acid substrate. The outcome of the cyclization was not influenced by the type of resin, the spacer, or the N-substituent. The analogous synthesis of the [6 + 7 + 5] fused ring system yielded inseparable diastereomers in a 1:0.6 ratio.Fil: Cankarova, Nadezda. Palacky University; República ChecaFil: la Venia, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Krajcovicova, Sona. Palacky University; República ChecaFil: Krchnak, Viktor. Palacky University; República Chec

Regioisomeric and substituent effects upon the outcome of the reaction of 1-borodienes with nitrosoarene compounds

A study of the reactivity of 1-borodienes with nitrosoarene compounds has been carried out showing an outcome that differs according to the hybridization state of the boron moiety. Using an sp2 boron substituent, a one-pot hetero-Diels–Alder/ring contraction cascade occurred to afford N-arylpyrroles with low to good yields depending on the electronic properties of the substituents on the borodiene, whereas an sp3 boron substituent led to the formation of stable boro-oxazines with high regioselectivity in most of the cases, in moderate to good yields. 1H and 11B NMR studies on two boro-oxazine regioisomers showed that selective deprotection can be performed. Formation of either the pyrrole or the furan derivative is pH- and regioisomer-structure-dependent. The results obtained, together with previous B3LYP calculations, support mechanistic proposals which suggest that pyrrole, or furan, formation proceeds via oxazine formation, followed by a boryl rearrangement and an intramolecular addition–elimination sequence

Former Menger School Trustees at 35th Anniversary

Portrait of former Menger School Trustees. There are two rows of men sitting in front of an unnamed building. Accompanying information lists the names of the men. "Seated L-R: H. Tietjen, John Wagner, H. Remmers, Chas. Menger, ---Jaehne; Standing: Wm. Stock, Ad. Brunkenhoefer, R. Dreyer, O. Zimmerman, E. Harbers, Hy. Kuck, Chas. Malina, Otto Glatzert.