1,1-Disubstituted styrenes with internal oxygen and nitrogen nucleophiles undergo oxidative fluorocyclization reactions with in situ generated chiral iodine(III)-catalysts. The resulting fluorinated tetrahydrofurans and pyrrolidines contain a tertiary carbon−fluorine stereocenter. Application of a new 1-naphthyllactic acid-based iodine(III)-catalyst allows the control of tertiary carbon− fluorine stereocenters with up to 96% ee. Density functional theory calculations are performed to investigate the details of the mechanism and the factors governing the stereoselectivity of the reaction.
Excellent enantioselectivities are observed in palladium-catalyzed allylic substitutions of a wide range of substrate types and nucleophiles using a bidentate ligand composed of oxazoline and chirally flexible biaryl phosphite elements. This unusually wide substrate scope is shown by experimental and theoretical studies of its η 3 -allyl and η 2 -olefin complexes not to be a result of configurational interconversion of the biaryl unit, since the ligand in all reactions adopts an S a ,S configuration on coordination to palladium, but rather the ability of the ligand to adapt the size of the substrate-binding pocket to the reacting substrate. This ability also serves as an explanation to its excellent performance in other types of catalytic processes.
The electrophilic fluorination of geminal alkyl substituted vinyl‐Bmida derivatives proceeds via bora‐Wagner–Meerwein rearrangement. According to DFT modelling studies this rearrangement occurs with a low activation barrier via a bora‐cyclopropane shaped TS. The Bmida group has a larger migration aptitude than the alkyl moiety in the Wagner–Meerwein rearrangement of the presented electrophilic fluorination reactions.
A method
for generation of Pd/phosphite-oxazoline catalysts containing
an alkyl backbone chain has been successfully applied to Pd-catalyzed
allylic substitution reactions. By carefully selecting the substituents
at both the alkyl backbone chain and the oxazoline of the ligand,
as well as the configuration of the biaryl phosphite group, high activities
(TOF > 8000 mol substrate × (mol Pd × h)−1) and excellent enantioselectivities (ee’s up to 99%) have
been achieved for many hindered and unhindered substrates with a wide
range of C-, O-, and N-nucleophiles (73 substitution products in total).
Moreover, DFT and NMR studies of the key Pd-allyl complexes allowed
us to better understand the origin of the excellent enantioselectivities
observed experimentally. The useful application of the Pd/phosphite-oxazoline
catalysts was demonstrated by the syntheses of many chiral carbobicycles,
with multiples stereocenters, by simple sequential reactions involving
Pd-allylic substitution and either 1,6-enyne cyclization or Pauson–Khand
enyne cyclization.
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