Visible‐Light Photoredox‐Catalyzed α‐Regioselective Conjugate Addition of Allyl Groups to Activated Alkenes

Abstract

The α‐regioselective conjugate addition of allyl groups to activated alkenes is a poorly explored area of research. Herein, we report an α‐adduct and (E)‐isomer selective conjugate addition of allylsilanes to activated alkenes by visible‐light photoredox catalysis. The reaction involves allylic radicals that can be generated from allylsilanes through a photoinduced single‐electron transfer mechanism.magnified image

Remote Giese Radical Addition by Photocatalytic Ring Opening of Activated Cycloalkanols

“…After 72 hours, the final products 5 a – c were obtained with moderate to good yields (Scheme 2a). In addition, to further prove the utility of the final products, it was possible to transform the malononitrile present in 3 a , into the versatile methyl ester group in very good yield by oxidative dehomologation with m ‐CPBA and Cs 2 CO 3 ( 6 , Scheme 2b) [13] …”

“…In addition, to further prove the utility of the final products, it was possible to transform the malononitrile present in 3 a, into the versatile methyl ester group in very good yield by oxidative dehomologation with m-CPBA and Cs 2 CO 3 (6, Scheme 2b). [13] Finally, the mechanism of the reaction was studied (Scheme 3). First, it was examined the formation of the hydrogen bond between the base and the alcohol 1 a by H-NMR.…”

Photochemical Organocatalytic Regio‐ and Enantioselective Conjugate Addition of Allyl Groups to Enals

“…benzylidene malononitrile) with a-regioselectivity (Figure 1 c). [11] We surmised that the reactivity of allylic radicals could be further leveraged to develop a conjugate addition to less activated enals 1. To implement this idea in an enantioselective setting, we exploited our recently reported strategy based on the photoexcitation of chiral iminium ions II, [12] generated upon condensation of a chiral amine catalyst with enals 1 (Figure 1 d).…”

“…A stereocontrolled radical coupling between I and the chiral 5p-electron b-enaminyl radical intermediate III, ensuing from the SET event, would eventually afford the chiral allylation product. Considering the steric profile of the intermediate III and the tendency of I to attack Michael acceptors with a-selectivity, [11] we envisaged that this strategy could provide a solution to the long-standing problem of achieving stereo-, regio-, and chemoselectivity in the conjugate allylation of enals 1.…”

Visible-Light Photoredox-Catalyzed Giese Reaction of α-Silyl Ethers with Various Michael Acceptors

“…Therefore, the development of neutral radical precursors having high atom economy and scalability is highly desirable. Recently, we developed neutral silicon-based alkyl radical precursors for the generation of alkoxylmethyl, , hydroxymethyl, and allylic radicals and reported the hydroalkoxymethylation of activated alkenes using α-trimethylsilyl-substituted ethers as alkoxymethyl radical precursors (Scheme a) . This reaction is mild and practical and exhibits high atom economy and good functional group tolerance.…”