Rhodium-Catalyzed Asymmetric Synthesis of 1,2-Disubstituted Allylic Fluorides

Although there are many methods for the asymmetric synthesis of monosubstituted allylic fluorides, construction of enantioenriched 1,2-disubstituted allylic fluorides has not been reported. To address this gap, we report an enantioselective synthesis of 1,2-disubstituted allylic fluorides using chiral diene-ligated rhodium catalyst, Et3 N ⋅ 3HF as a source of fluoride, and Morita Baylis Hillman (MBH) trichloroacetimidates. Kinetic studies show that one enantiomer of racemic MBH substrate reacts faster than the other. Computational studies reveal that both syn and anti π-allyl complexes are formed upon ionization of allylic substrate, and the syn complexes are slightly energetically favorable. This is in contrast to our previous observation for formation of monosubstituted π-allyl intermediates, in which the syn π-allyl conformation is strongly preferred. In addition, the presence of an electron-withdrawing group at C2 position of racemic MBH substrate renders 1,2-disubstituted π-allyl intermediate formation endergonic and reversible. To compare, formation of monosubstituted π-allyl intermediates was exergonic and irreversible. DFT calculations and kinetic studies support a dynamic kinetic asymmetric transformation process wherein the rate of isomerization of the 1,2-disubstituted π-allylrhodium complexes is faster than that of fluoride addition onto the more reactive intermediate. The 1,2-disubstituted allylic fluorides were obtained in good yields, enantioselectivity, and branched selectivity.

Unveiling the abnormal effect of temperature on enantioselectivity in the palladium-mediated decabonylative alkylation of MBH acetate

An unusual temperature–enantioselectivity relationship was observed in the newly developed palladium-catalysed enantioselective nucleophilic substitution of cyclic Morita–Baylis–Hillman acetate and 4,4,4-trifluoro-1-phenyl-1,3-butanedione.

Catalytic mutual multicomponent reaction: facile access to α-trifluoromethylthiolated ketones

A multicomponent catalytic reaction between ketones, Morita-Baylis-Hillman (MBH) carbonates and trifluoromethylthiolating agents is devised for straightforwardly accessing two products, α-trifluoromethylthiolated ketones and α-methylene β-amino esters in a one pot fashion. Particularly noteworthy is that the trifluoromethylthiolating reagent is employed as both the nitrogen and SCF3 source initiated by DABCO. This mild one pot strategy enjoys atom- and step-economic attractiveness, for direct introduction of an SCF3 group onto a variety of acyclic ketones, which have been considered as less effective and less developed substrates.

Silver/palladium relay catalyzed 1,3-dipole annulation/allylation reactions to access fully substituted allyl imidazolidines

A silver/palladium relay catalyzed 1,3-dipole annulation/allylation reaction of iminoesters and Baylis-Hillman acetates for the construction of fully substituted allyl imidazolidines is reported. The reaction of both iminoesters and Baylis-Hillman acetates affords the fully substituted allyl imidazolidines in high yields and regioselectivities. The three component reaction is triggered by silver-catalyzed 1,3-dipole annulation, followed by the sequential palladium catalyzed allylation. Mechanistic studies reveal that the dual catalytic system plays a key role in the reaction. The developed methodology provides straightforward access to allyl imidazolidines under simple reaction conditions.

Palladium-Catalyzed Asymmetric Allylic Alkylations of Colby Pro-Enolates with MBH Carbonates: Enantioselective Access to Quaternary C-F Oxindoles

Owing to the innovative applications of fluorinated compounds in many areas of technology and medicine, methods for the preparation of C-F quaternary fluorine containing compounds are in extremely high demand. Here, we report the discovery of a general procedure for an S_N 2 reaction catalyzed by Pd/Ding-SKP-type ligands, and that occurs between Colby pro-enolates with MBH carbonates to afford the corresponding products featuring two consecutive stereogenic carbons, including a C-F quaternary stereogenic center. The reactions readily occur at ambient temperatures with high chemical yields and in excellent chemo-, diastereo- and enantioselective manners. This practically attractive stereochemical outcome, coupled with the operational simplicity and structural generality, bodes well for the synthetic application of this process in the preparation of a novel class of biologically relevant fluorine-containing compounds.

Palladium-catalyzed asymmetric allylic amination: enantioselective synthesis of chiral α-methylene substituted β-aminophosphonates

Palladium catalyzed asymmetric allylic amination of 2-diethylphosphonate-substituted allylic acetates in the presence of SKP ligands afforded the corresponding chiral β-aminophosphonates in good yields, high regioselectivities, and excellent enantioselectivities.