Photoinduced C(sp³)−N Bond Cleavage Leading to the Stereoselective Syntheses of Alkenes

Abstract

Herein we report av ersatile Mizoroki-Heck-type photoinducedC (sp 3 )ÀNb ond cleavage reaction. Under visible-light irradiation (455 nm, blue LEDs) at room temperature, alkyl Katritzkys alts react smoothly with alkenes in a1 :1 molar ratio in the presence of 1.0 mol %o fc ommercially available photoredoxc atalyst without the need for any base, affording the correspondingalkyl-substituted alkenesi ng ood yields with broad functional-groupc ompatibility.N otably,t he E/Z-selectivity of the alkene products can be controlled by an appropriate choice of photoredox catalyst.Alkenesa re essential building blocks for organic synthesis, and are ubiquitous in the fields of life science, drug discovery,a nd materials science.T he different configurational isomers (E and Z)o fa lkenes usually display distinct physicochemical properties and physiological activities, [1] and so stereoselective synthesis of alkenes has long been of great interest to synthetic chemists. Currently,t he Mizoroki-Heck (MÀH) reaction, [2] which is aP d-catalyzedc ross-coupling reactionb etween alkenes and aryl/vinyl halides, is regarded as one of the most useful protocols for the selective synthesis of substituted alkenes. [3] However,d espite the high efficiency and applicability of the Pd-catalyzed reaction, it has some limitations.F or example, methodology for cross-couplingb yu sing aliphatic halides, especially those possessingab-hydrogen atom, is still limited due to the occurrence of rapid b-H elimination as as ide reaction. Further,t he configuration of the formed C=Cb ond is determined by the transition structure at the syn-extrusions tep (periplanar ÀPdÀCÀCÀHÀ 4-membered ring), and hence external control of the E/Z selectivityb yc hanging the catalysto r ligand is difficult.T hus, althoughe legante xamples of the Pdcatalyzed reactioni nvolving alkyl halides have been report-

Pyridinium Salts as Redox‐Active Functional Group Transfer Reagents

“…[43] Under basic conditions,t he transiently generated radical resulting from the addition of the alkyl radical to the olefin undergoes oxidation by the reduced photocatalyst and elimination to afford Heck-type products. [44] Notably,H eck-type deaminative alkylation of N-alkyl pyridinium salts can also be mediated efficiently by triphenylphosphine and sodium iodide under irradiation with visible light. [45] Allylic sulfones efficiently participate in radical allylation reactions,t hereby enabling the formation of C-(sp 3 ) À C(sp 2 )bonds.…”

Pyrylium Salts: Selective Reagents for the Activation of Primary Amino Groups in Organic Synthesis

“…Scheme 18 Alkyl-Heck-type reactions of alkylpyridinium salts Also in 2019, Uchiyama, Wang, and co-workers reported stereoselective alkyl-Heck-type reactions (Scheme 18). 66 Pyridinium salts derived from amino acids reacted with styrenes to yield the corresponding alkenes with Z selectivity using fac-Ir(ppy) 3 or E selectivity using [Ru(bpy) 3 ](PF 6 ) 2 . Other ester-, cyano-or benzyl-stabilized pyridinium salts were also amenable in this protocol.…”

Photocatalytic Synthesis of Stilbenes via Cross‐Coupling of Alkenyl Boronic Acids and Arenediazonium Tetrafluoroborate Salts

“…While the selectivities for E-stilbenes together with eosin Y were very high, almost pure Z-stilbenes could be obtained when using Ru(bpy) 3 Cl 2 as photocatalyst. This phenomenon has been described most recently by the groups of Uchiyama [38] and Yu [39] (Scheme 2). In order to find out whether the conversion of (E)-boronic acid to Z-stilbene in the presence of Ru(bpy) 3 Cl 2 follows its own mechanism or is a conversion to Estilbene with subsequent isomerization, a monitoring was performed (c).…”