Tandem superelectrophilic activation for the regioselective chlorofluorination of recalcitrant allylic amines

Superacid-Synthesized Fluorinated Diamines Act as Selective hCA IV Inhibitors

Carbonic anhydrase (CA) IV is a membrane-bound enzyme involved in important physio-pathological processes, such as excitation-contraction coupling in heart muscle, central nervous system (CNS) extracellular buffering, and mediation of inflammatory response after stroke. Known since the mid-1980s, this isoform is still largely unexplored when compared to other isoforms, mostly for the current lack of inhibitors targeting selectively this isoform. The discovery of selective CA IV inhibitors is thus largely awaited. In this work, we report β-(di) fluoropropyl diamines as effective CA IV inhibitors, opening real perspectives for a new mode of selective inhibition of this isoform. Inhibition data reveal that the essential structure core to ensure a potent and selective inhibition of CA IV is the N-propyldiamine. Molecular modeling studies were employed to understand the binding mode of the synthesized amines. Conformational searches within the active site space carried out in an implicit solvent (water) model were also conducted.

Diastereodivergent nucleophile-nucleophile alkene chlorofluorination

The selective hetero-dihalogenation of alkenes provides useful building blocks for a broad range of chemical applications. Unlike homo-dihalogenation, selective hetero-dihalogenation reactions, especially fluorohalogenation, are underdeveloped. Current approaches combine an electrophilic halogen source with a nucleophilic halogen source, which necessarily leads to anti-addition, and regioselectivity has only been achieved using highly activated alkenes. Here we describe an alternative, nucleophile-nucleophile approach that adds chloride and fluoride ions over unactivated alkenes in a highly regio-, chemo- and diastereoselective manner. A curious switch in the reaction mechanism was discovered, which triggers a complete reversal of the diastereoselectivity to promote either anti- or syn-addition. The conditions are demonstrated on an array of pharmaceutically relevant compounds, and detailed mechanistic studies reveal the selectivity and the switch between the syn- and anti-diastereomers are based on different active iodanes and which of the two halides adds first.

Understanding the Role of Protic Ionic Liquids (PILs) in Reactive Systems: Rational Selection of PILs for the Design of Green Synthesis Strategies for Allylic Amines and β-Amino Esters

The reactive behaviour of protic ionic liquids (PILs) has been shown to be governed not only by their chemical structures but also by their global compositions, which include the presence of free acids and bases at equilibrium with ionic pairs. Six PILs composed of primary, secondary, or tertiary alkyl ammonium cations with two couterions, nitrate or acetate, were tested in model reactions with unsaturated substrates. The free species that were naturally present in these liquids were identified by cyclic voltammetry. Only tributylammonium nitrate was found to be mostly composed just of the ionic pair; the other five PILs also contain variable amounts of free acid and amine. In reactive systems, these free species determine the products of the reaction. In particular, allylic amines and β-amino esters were obtained in good yields (91 and 75 %, respectively) by reaction of conjugated dienes and acrylates in the presence of PILs. By taking into account the actual composition of each PIL, it was possible to direct the reaction path towards a specific product with good yields, to ensure acid catalysis, to avoid polymerization of the substrate, and to promote phase transfer of products. These results establish some useful guidelines for the rational design of new PIL-based one-step synthetic strategies.

Triazine-Based Cationic Leaving Group: Synergistic Driving Forces for Rapid Formation of Carbocation Species

A new triazine-based cationic leaving group has been developed for the acid-catalyzed alkylation of O- and C-nucleophiles. There are two synergistic driving forces, namely, stable C═O bond formation and charge-charge repulsive effects, involved in the rapid generation of the carbocation species in the presence of trifluoromethanesulfonic acid (∼200 mol %). Considerable rate acceleration of benzylation, allylation, and p-nitrobenzylation was observed as compared to the reactions with less than 100 mol % of the acid catalyst. The triazine-based leaving group showed superior p-nitrobenzylation yield and stability in comparison to common leaving groups, trichloroacetimidate and bromide. A plausible reaction mechanism (the cationic leaving group pathway) was proposed on the basis of mechanistic and kinetic studies, NMR experiments, and calculations.

Cationic polycyclization of ynamides: building up molecular complexity

Polycyclization reactions are among the most efficient synthetic tools for the synthesis of complex, polycyclic molecules in a single operation from simple starting materials. We report in this manuscript a full account on the discovery and development of a novel cationic polycyclization from readily available ynamides. Simple activation of these building blocks under acidic conditions enables the generation of highly reactive activated keteniminium ions, which triggers an unprecedented cationic polycyclization yielding highly substituted polycyclic nitrogen heterocycles possessing up to seven fused cycles and three contiguous stereocenters.