A Palladium/Light System Combined with Hanztsch Ester: Radical Vinylation of Alkyl Iodides with Vinyl Bromides

Abstract

Radical vinylation of alkyl iodides with vinyl bromides proceeds smoothly with ac ombinedP d/light/ Hanztsch ester system. In this reaction system,t he Hanztsch ester acts as an effective reducing reagent of Pd II to Pd 0 that generates key alkyl radicals via single electron transfer (SET) with alkyl iodides upon photo-excitation.Transition-metal-catalyzed cross-coupling reactions provide au seful meansf or CÀCb ond formingp rocesses and recent effort has been directed to expandt he substrate scope to include sp 3 -hybridized alkyl halides. [1,2] We have been engaged in developingaseries of cascade reactions of alkyl iodides, CO, and alkenes using aP d/light combined system. [3][4][5] Recently we reportedt hat using aP d/light combined system, Giese-type reactions of alkyl iodides with electron deficient alkenes proceed in the presence of Hanztsch ester as the hydrogen source. [6] The first step of the Pd/light system is SET between Pd 0 and R-I to form the RC and Pd I -I pair and we thought that the Pd/ light system would thus be usefula lso for radicalv inylation employing vinyl bromides.[7] To achieve the equivalent reaction of the Mizoroki-Heck reaction of alkyl halides [Eq. (1), Scheme 1],w ep ostulated that the Pd/light-induced radical addition/fragmentation sequence was promising[ Eq. (2), Scheme 2]. [8,9] If key radicals speciesa re generated from alkyl halides, the leaving BrC has to be converted to an alkyl radical in order to sustain the radical chain. Currently,aseries of vinylation reactions by radical addition/fragmentation sequences are known, using vinyltins, [10] vinyl sulfides, [11] vinyl sulfones, [12] nitroalkenes, [13] vinylindiums, [14] vinylgalliums, [14b] vinyl chlorides, [15] and vinyl bromides. [16] In as tudy by Singleton, [16a] hexabutylditin was added to sustain the radicalc hain by converting bromine radical to tributyltin radical. If an appropriate reducing system that regenerates Pd 0 could be identified, radical vinylation systems based on SET between alkyl iodides and Pd 0 would be useful, [Eq. (2), Scheme 1].I nt his paper we report aP d/light system combined with Hanztsch ester A as au seful tool to achieve radical vinylation of alkyl iodides with vinyl bromides.We examined the reaction of iodocyclohexane (1a)

Aryldiazonium Salts and DABSO: A Versatile Combination for Three‐Component Sulfonylative Cross‐Coupling Reactions

“…The reaction gives similar yields either under inert or aerial atmosphere which concludes that DABCO radical cation is solely responsible for the oxidation of intermediate I Finally, base promoted deboronation from J with E ‐selectivity provides the desired E ‐vinylsulfone [13] . In case of vinyl halide, we anticipated that radical vinylation via β‐scission of halide furnished the desired product [7n,o] …”

On Water Pictet‐Spengler Reaction of Tryptophan followed by Buchwald Coupling for the Synthesis of Natural Products Stellarines A, B and β‐Carboline Derivatives: Their Molecular Docking against SARS‐CoV‐2 MPro

“…The amidated product first undergoes deprotection of amide nitrogen to form compound 7 (Stellarines A). This compound 7 undergoes coupling with acrylates (8) [28][29][30]…”

Palladium/Light Induced Radical Alkenylation and Allylation of Alkyl Iodides Using Alkenyl and Allylic Sulfones

“…In order to sustain the radical chain, the leaving radical Y • has to trigger a propagation sequence, and hexabutylditin is often used to facilitate this process (Scheme , eq 3) . Thus far, a number of alkenylating reagents has been examined in different types of radical alkenylation reactions, which include alkenyltins, alkenylsulfides, alkenyl sulfones, , nitroalkenes, alkenylindiums, alkenylgalliums, alkenyl chlorides, and alkenyl bromides. − Also, the radical allylation reactions following a related mechanistic pathway have been investigated (Scheme , eq 2). ,,, As part of our research program in developing Pd/light-initiated radical reactions, , we recently reported a coupling reaction of alkyl iodides and alkenyl bromides with Hanztsch ester as a reducing agent (Scheme , eq 4) . In this reaction system, the single electron transfer (SET) reaction between alkyl iodides and Pd(0) under photoirradiation is responsible for the generation of the initial alkyl radical, and Hanztsch ester serves an essential role in reducing Pd­(II)­IBr to Pd(0) to sustain radical chain.…”

“…Et 3 N was necessary for the reaction to proceed (Table , entry 6). The addition of Hantzsch ester did not improve the yield, in contrast to our previous report on the alkenylation with alkenyl bromides (Table , entry 7). In the absence of PdCl 2 , LiCl, and t -BuNC, no alkenylation reaction took place (Table , entry 8).…”