Chiral phosphoric acid-catalyzed asymmetric aldehyde prenylation has been established using an α,α-dimethyl allyl boronic ester. The transformation provides an expedient access to a wide array of aryl, heteroaryl, aryl-substituted alkenyl...
The 1,3‐dipolar cycloadditions of β‐fluoroalkyl vinylsulfones and nitrile oxides to deliver 5‐fluoroalkyl‐3‐substituted 2‐isoxazolines has been established under mild conditions in up to 85% yield with excellent regio‐ and diastereoselectivities (all d.r. >99 : 1), and thus facilitated rapid access to 5‐fluoroalkyl‐3‐Ph‐2‐isoxazoles by DBU‐mediated elimination of the pyridyl sulfone group.
Asymmetric Petasis allylboration among an aldehyde, 1,2-amino alcohol and pinacolallylboronate has been established at room temperature without any catalysts.
With
the aim of developing novel annulations via ketene intermediates,
allenyl imide and alkynoates bearing good leaving groups are used
for their function in a tandem conjugate addition–elimination
reaction (SN2′ type) promoted by nucleophilic phosphine catalysts.
By utilizing thioamides as 1S,3N-bis-nucleophiles, [3+3] and [3+2] annulations have been established
to allow rapid access to 1,3-thiazin-4-ones and 5-alkenyl thiazolones
in high yields, respectively. Furthermore, the possible reaction mechanisms
are proposed on the basis of deuterium labeling experiments and density
functional theory calculations.
ACu II -catalyzed asymmetric 1,3-dipolar cycloaddition using b-fluoroalkyl alkenyl arylsulfones as dipolarophiles and glycine/alanine iminoesters as azomethine ylide precursors has been developed. Remarkably,acatalyst loading as low as 0.5 mol %i sh ighly efficient. Accordingly,awide range of enantioenriched 3-fluoroalkylp yrrolidines,a sw ell as D 2pyrroline and pyrrole derivatives,a re generated in good to excellent yields with high asymmetric induction. This synthetic approach is diastereodivergent in that exo-adducts could be converted into the corresponding exo'-adducts by 1, 8diazabicyclo[5.4.0]undec-7-ene mediated epimerization at C2 of the pyrrolidine core.T he free-energy profiles from DFT calculations suggest the Michael addition of the 1,3-dipole to be the rate-and enantiodetermining step,a nd the origin of stereoselectivity is studied by means of the noncovalent interaction (NCI) analysis.
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