Thiourea-Mediated Halogenation of Alcohols.

The halogenation of alcohols under mild conditions expedited by the presence of substoichiometric amounts of thiourea additives is presented. The amount of thiourea added dictates the pathway of the reaction, which may diverge from the desired halogenation reaction toward oxidation of the alcohol, in the absence of thiourea, or toward starting material recovery when excess thiourea is used. Both bromination and chlorination were highly efficient for primary, secondary, tertiary, and benzyl alcohols and tolerate a broad range of functional groups. Detailed electron paramagnetic resonance (EPR) studies, isotopic labeling, and other control experiments suggest a radical-based mechanism. The fact that the reaction is carried out at ambient conditions, uses ubiquitous and inexpensive reagents, boasts a wide scope, and can be made highly atom economic, makes this new methodology a very appealing option for this archetypical organic reaction.

Inherently Chiral Bambus[4]urils.

A new class of bambus[4]urils (BU[4]s) composed of asymmetric N,N'-disubstituted glycoluril subunits with different alkyl groups were designed, synthesized, and fully characterized by NMR techniques and X-ray crystallography. Structural studies showed that four macrocyclic diastereoisomers are possible: two Sn symmetric achiral macrocycles and two macrocycles that are "inherently" chiral. The relative "head-to-tail" arrangement of the N-substituents in Bn4Me4BU[4], 5a, clearly observed by X-ray spectroscopy analysis, determines the overall symmetry of the bambusuril structure. Chiral Pr4Me4BU[4], 4b, was resolved by chiral high-performance liquid chromatography (HPLC) into its enantiomers, and all four inherently chiral bambusuril pairs (two Pr4Me4BU[4] and two Bn4Me4BU[4] stereoisomers, 4b, 4d, 5b, and 5d) were clearly observed by 1H NMR spectroscopy with the aid of (R)-BINOL as a chiral solvating agent. This latter methodology provides a rapid and powerful approach for investigating the enantiopurity of inherently chiral cavitands, which complements and augments the conventional chromatographic approaches.

Semithiobambus[6]uril is a transmembrane anion transporter.

Semithiobambus[6]uril is shown to be an efficient transmembrane anion transporter. Although all bambusuril analogs (having either O, S or N atoms in their portals) are excellent anion binders, only the sulfur analog is also an effective anion transporter capable of polarizing lipid membranes through selective anion uniport. This notable divergence reflects significant differences in the lipophilic character of the bambusuril analogs.

A practical and convenient protocol for the synthesis of (E)-α,ß-unsaturated acids.

α,ß-Unsaturated acids are very useful and versatile reagents in organic synthesis. A novel, practical, and convenient catalytic protocol comprising FeCl3·6H2O (0.5 mol %) and H2O (1 equiv) in CH3NO2 is described for the rapid synthesis of α,ß-unsaturated acids with high E-stereoselectivity under both microwave and conventional heating conditions with high TON and TOF values. This powerful approach efficiently demonstrated the utility of biomass derived aldehydes to build chemical agents used as fuel additives. The method proved to be scalable to gram scale synthesis.

Enantiopure synthesis of side chain-modified α-amino acids and 5-cis-alkylprolines.

A short, concise synthesis of enantiopure, side chain-modified α-amino acids such as 4-oxo-L-norvaline, 6-oxo-L-homonorleucine, and 5-cis-alkyl prolines is described. Knoevenagel condensation of l-aminocarboxylate-derived ß-ketoesters with aldehydes followed by reductive decarboxylation results in unnatural α-amino acids in good yield. A fluorescent amino acid is synthesized using a similar protocol. These studies show that aminocarboxylate-derived ß-ketoesters are very useful intermediates and the method employed is both general and practical for the preparation of γ(δ)-oxo α-amino acids and alkylprolines.