Quantification of amino groups on halloysite surfaces using the Fmoc-method.

The functionalization of halloysite nanotube (HNT) surfaces with aminosilanes is an important strategy for their further decoration with organic molecules to obtain hybrid inorganic-organic nanoarchitectures to be used in catalysis and drug delivery. The exact quantification of amino groups on the surface is an important aspect in view of the obtainment of systems with a known number of loaded molecules. In the present study, we describe a simple and reliable method for the correct quantification of groups present on HNT surfaces after their reaction with aminopropyltriethoxysilane (APTES). This method, applied for the first time to HNT chemistry, was based on the use of Fmoc groups as probes covalently bound to APTES and quantified by UV-Vis after release from the HNT-APTES-Fmoc system. Interestingly, this method showed great accordance with the already employed quantitative thermogravimetric analysis (TGA), with some benefits such as simple and non-destructive procedure, besides the possibility to monitor the deprotection reaction.

Fe-Catalyzed C-C Bond Construction from Olefins via Radicals.

This Article details the development of the iron-catalyzed conversion of olefins to radicals and their subsequent use in the construction of C-C bonds. Optimization of a reductive diene cyclization led to the development of an intermolecular cross-coupling of electronically-differentiated donor and acceptor olefins. Although the substitution on the donor olefins was initially limited to alkyl and aryl groups, additional efforts culminated in the expansion of the scope of the substitution to various heteroatom-based functionalities, providing a unified olefin reactivity. A vinyl sulfone acceptor olefin was developed, which allowed for the efficient synthesis of sulfone adducts that could be used as branch points for further diversification. Moreover, this reactivity was extended into an olefin-based Minisci reaction to functionalize heterocyclic scaffolds. Finally, mechanistic studies resulted in a more thorough understanding of the reaction, giving rise to the development of a more efficient second-generation set of olefin cross-coupling conditions.

A practical and stereoselective organocatalytic alkylation of aldehydes with benzodithiolylium tetrafluoroborate.

Recently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved via SN 1-type reactions with catalytic amounts of Brønsted or Lewis acids. When a new stereogenic center is formed most of these transformations produce the desired product as a racemate, as these reactions proceed through carbenium ions. The arsenal of activation modes available in organocatalysis can be used to set up suitable reaction conditions in which chiral nucleophiles (enamine catalysis) or chiral electrophiles (iminium catalysis, chiral counterion catalysis) can easily be generated. Recently, we have used stabilized carbenium ions, directly available or obtained from the corresponding alcohols, in new organocatalytic stereoselective SN 1-type reactions. The commercially available carbenium ion benzodithiolylium tetrafluoroborate can be used for the straightforward organocatalytic stereoselective alkylation of aldehydes. In this account we will illustrate the application of this methodology in the total synthesis of natural products and the preparation of valuable starting materials.