Visible-Light Decatungstate/Disulfide Dual Catalysis for the Hydro-Functionalization of Styrenes

Abstract

We describe an efficient photoredox system, relying on decatungstate/disulfide catalysts, for the hydrofunctionalization of styrenes. In this methodology the use of disulfide as co-catalyst was shown to be crucial for the reaction efficiency. This photoredox system was employed for the hydro-carbamoylation, -acylation, -alkylation and -silylation of styrenes, giving access to a large variety of useful building blocks and high-value molecules such as amides and unsymmetrical ketones from simple starting materials.

[3+2] Cycloaddition of alkyl aldehydes and alkynes enabled by photoinduced hydrogen atom transfer

“…Some deuterium-labeling experiments were then conducted. Almost no deuterium incorporation was observed with CD 3 CN as the solvent, while Based on the above results and previous reports [20][21][22][23][24][25][26][27][28][29][30][31][32][33] , a plausible mechanism for this TBADT-catalyzed [3+2] cycloaddition is proposed in Fig. 5.…”

“…Despite these significant advances, it is still highly desirable to develop novel [3+2] annulation for the atom-economic and controllable synthesis of polysubstituted cyclopentanones, particularly using readily available 3C synthons. In light of recent developments on decatungstatecatalyzed C-H functionalization of aldehydes [20][21][22][23][24][25][26][27][28][29][30][31][32][33] and our interest 34 on 5-endo-trig radical cyclization of all-carbon systems, we envisioned that abundant aliphatic aldehydes could be exploited as an ideal 3C component for the [3+2] carbocyclization of alkynes via the hydrogen atom transfer (HAT) [35][36][37][38][39][40] -induced double C-H functionalization (Fig. 1c).…”

Photocatalytic Hydroaminoalkylation of Styrenes with Unprotected Primary Alkylamines

“…Reduction of this radical to the corresponding carbanion 27 by the [3DPA2FBN] −• radical anion [ E 1/2 (PC/PC –• ) = −1.92 V vs SCE in MeCN] is presumably followed by proton transfer from HN 3 (p K a = 7.9 in DMSO) to give the γ-aryl­amine product 7 and regenerate the azide ion. Alternatively, a chain process involving HAT from HN 3 (BDE = 93 kcal mol –1 ) to the benzylic radical 26 (BDE = 85.4 ± 1.5 kcal mol –1 for PhC H 2 Me) can be envisaged . To probe the latter possibility, the reaction quantum yield (Φ prod ) was measured for the reaction of cyclohexyl­amine 1a with styrene 6b and found to be 0.31 (at 66% conversion to 7ab by NMR) .…”

“…Alternatively, a chain process involving HAT from HN 3 (BDE = 93 kcal mol –1 ) to the benzylic radical 26 (BDE = 85.4 ± 1.5 kcal mol –1 for PhC H 2 Me) 20 can be envisaged. 51 To probe the latter possibility, the reaction quantum yield (Φ prod ) was measured for the reaction of cyclohexylamine 1a with styrene 6b and found to be 0.31 (at 66% conversion to 7ab by NMR). 52 Given that quantum efficiencies for dual catalytic photoredox processes in which a cocatalyst is the quencher are typically very low (Φ prod < 0.1), 9d , 53 a value of 0.31 is suggestive of at least some contribution from an innate chain (with a photonically inefficient initiation step).…”

Nickel/Photo-Cocatalyzed C(sp2)–H Allylation of Aldehydes and Formamides

“…To establish a new strategy for the C­(sp 2 )–H allylation of a formyl moiety, we turned our attention to the cooperative catalysis of nickel and tetrabutylammonium decatungstate (TBADT), which has been applied in cross-coupling reactions involving hydrocarbons or aldehydes. − In our hypothesis, the hydrogen-atom-transfer (HAT) photocatalyst TBADT promotes radical-type umpolung of aldehydes or formamides via homolytic acyl C–H bond cleavage under irradiation, whereas low-valent nickel interacts with electrophilic allyl alcohols or their derivatives to form a π-allylnickel intermediate . The following coupling of these two species generated by distinct catalysts would provide novel access to β,γ-unsaturated ketones or amides (Scheme B).…”