Catalytic, Enantioselective 1,2-Difluorination of Cinnamamides.

The enantio- and diastereoselective synthesis of 1,2-difluorides via chiral aryl iodide-catalyzed difluorination of cinnamamides is reported. The method uses HF-pyridine as a fluoride source and mCPBA as a stoichiometric oxidant to turn over catalyst, and affords compounds containing vicinal, fluoride-bearing stereocenters. Selectivity for 1,2-difluorination versus a rearrangement pathway resulting in 1,1-difluorination is enforced through anchimeric assistance from a N- tert-butyl amide substituent.

BF-Promoted, Carbene-like, C-H Insertion Reactions of Benzynes.

Boron trifluoride is observed to promote a variety of C-H insertion reactions of benzynes bearing pendant alkyl groups. Computations and various mechanistic studies indicate that BF engages the strained π-bond to confer carbene-like character on the adjacent, noncoordinated benzyne carbon. This represents an unprecedented catalytic role for a non-transition metal such as BF.

Mechanism and Origins of Chemo- and Stereoselectivities of Aryl Iodide-Catalyzed Asymmetric Difluorinations of β-Substituted Styrenes.

The mechanism of the aryl iodide-catalyzed asymmetric migratory geminal difluorination of β-substituted styrenes ( Banik et al. Science 2016, 353, 51 ) has been explored with density functional theory computations. The computed mechanism consists of (a) activation of iodoarene difluoride (ArIF), (b) enantiodetermining 1,2-fluoroiodination, (c) bridging phenonium ion formation via S2 reductive displacement, and (d) regioselective fluoride addition.

Mechanism of the reactions of alcohols with o-benzynes.

We have studied reactions of secondary and primary alcohols with benzynes generated by the hexadehydro-Diels-Alder (HDDA) reaction. These alcohols undergo competitive addition vs dihydrogen transfer to produce aryl ethers vs reduced benzenoid products, respectively. During the latter process, an equivalent amount of oxidized ketone (or aldehyde) is formed.