Stereoselective and Atom-Economic Alkenyl C–H Allylation/Alkenylation in Aqueous Media by Iridium Catalysis

Abstract

A practical and atom-economic protocol for the stereoselective preparation of various 1,4-and 1,3-diene skeletons through iridium-catalyzed directed olefinic C−H allylation and alkenylation of NH-Ts acrylamides in water was developed. This reaction tolerated a wide scope of substrates under simple reaction conditions and enabled successful gram-scale preparation. Furthermore, an asymmetric variant of this reaction giving enantioenriched 1,4-dienes was achieved employing a chiral diene−iridium complex as the catalyst.

Recent Advances in Alkenyl sp2 C–H and C–F Bond Functionalizations: Scope, Mechanism, and Applications

“…Successfully, they further expanded to carry out this olefinic C−H allylation of NH-Ts acrylamides in water, efficiently affording the corresponding skipped 1,4-dienes in excellent yields (52− 99%). 285 Moreover, Krische's group in 2009 established a chelationdirected C−H allylation of α,β-unsaturated carboxamides via the addition of vinylic C(sp 2 )−H bonds to 1,1-dimethylallenes catalyzed by a cationic iridium complex assembled from [Ir(cod) 2 ]BAr F 4 and rac-BINAP (Scheme 165), 286 resulting in the adduct products of C−H prenylation in good yields as single isomers.…”

“… This atom-economic C–H allylation took place with the assistance of a NH-Ts amide group under additive-and ligand-free conditions. Successfully, they further expanded to carry out this olefinic C–H allylation of NH-Ts acrylamides in water, efficiently affording the corresponding skipped 1,4-dienes in excellent yields (52–99%) …”

Chiral Diene Ligands in Asymmetric Catalysis

“…The asymmetric olefinic C–H allylation of N -tosylacrylamide 316 with 1,3-dienes 317 to give enantioenriched 1,4-dienes 318 using the chiral diene–iridium catalyst [IrCl­(( S,S )- L15c )] 2 has been reported (Scheme b) . The olefinic hydridoiridium­(III) species B may be involved in the catalytic cycle.…”

Chelation-assisted iridium-catalyzed hydroalkenylation and hydroarylation/cyclization with conjugated trienes

“…Very recently, our group developed an iridium-catalyzed olefinic C–H allylation of acrylamides to synthesize skipped dienes by hydroalkenylation of conjugated dienes under chelation assistance, representing an atom efficient method with an excellent E / Z selectivity (Scheme 1b). 7 Considering the challenging preparation and high value of 1,4,6-trienes, we herein examined the possibility of 1,4,6-triene synthesis by a directed hydroalkenylation strategy using conjugated trienes. However, the more double bonds that exist in polyene substrates, the greater the increase in reaction complexity due to olefin isomerization/migration, as well as to the competitive formation of π-allyliridium intermediates.…”

“…At the beginning of our study, we examined a cross-coupling between NH-Ts acrylamide 1a and 1,3,5-triene 2a to afford the desired product 3a in a 65% yield in methanol at room temperature, introducing robust [Ir(OMe)(cod)] 2 as the catalyst, which was previously used in hydroalkenylation reactions using 1,3-dienes (Table 1, entry 1). 7 Simply heating to 60 °C further improved the product yield to 78%, and no olefin migration and isomerization was observed (entry 2). Using [IrCl(cod)] 2 as the catalyst instead led to a moderate yield, employment of [IrCp*Cl 2 ] 2 totally retarded the reaction (entries 3 and 4).…”