Highly stereoselective carbon-functionalization of electron-deficient arylalkenes by use of organosilicon compounds via photoinduced electron transfer

Smooth Photocatalyzed Benzylation of Electrophilic Olefins via Decarboxylation of Arylacetic Acids

“…The present work compares favorably with other decarboxylative photocatalytic strategies employing arylacetic acids and is complementary to them, since this is one of the rare examples of electron-poor olefin benzylation. − The proposed reaction mechanism is gathered in Scheme and is strengthened by the electrochemical investigation reported above. Given the unknown reduction potential of wO (up to +2.61 V vs SCE), , the occurrence of an electron transfer from 1a ( E 1/2 OX ( 1a •+ / 1a ) = +2.51 V vs SCE, Table ) to wO cannot be excluded.…”

“…Benzyl radicals were generated from phenylacetic acids and used as well, but not in the benzylation of olefins, due to the lack of reactivity of these radicals toward CC double bonds. A way to overcome the problem makes use of easily reducible olefins. − Scheme shows our proposed plan to benzylate olefins starting from phenylacetic acids 1 (used as the corresponding carboxylate anions 1 – ). The photocatalytic generation of the benzyl radical should be followed by regeneration of the photocatalyst via reaction with the olefin 2 .…”

Diastereoselective protonation on a radical anion in the photoallylation and photoreduction of 1,1-dicyano-2-methyl-3-phenyl-1-butene by allyltrimethylsilane

“…In these photoreactions, radical anions generated from the electron-deficient molecules and carbon radicals generated from radical cations of the organosilicon compounds are postulated as reactive intermediates. However, control of stereoselectivity in the PET reaction has been less discussed so far [12][13][14][15]. We have previously reported that PET reaction of cycloalkylidenepropanedinitriles with allylic silanes afforded allylated products at a-carbon of cyano groups and reduction products in a highly diastereoselective manner [16].…”

Enantioselective Protonation of Radical Anion Intermediates in Photoallylation and Photoreduction Reactions of 3,3-Diaryl-1,1-dicyano-2-methylprop-1-ene with Allyltrimethylsilane

“…Each photoreaction described above takes place through a process termed photoredox sensitization by phenanthrene (Phen) (Scheme 4) [22,23,24,25,26,27]. In the pathway, the excited singlet state of Phen, generated by light absorption, transfers one electron (SET (single electron transfer)) to the electron-deficient alkene 1 to form the phenanthrene radical cation (Phen •+ ) and the alkene radical anion 1 •− .…”

“…We have previously developed photoallylation and photoreduction reactions of electron deficient alkenes with allyltrimethylsilane that occur via PET pathways [22,23,24]. In addition, we also demonstrated that diastereoselectivity of this process can be achieved by steric control of allyl radical or proton addition to radical anions that are generated from electron deficient alkenes (Scheme 1) [25,26,27]. The current study was aimed at the development of enantioselective PET promoted coupling reactions, and specifically, at assessing the effect of chiral carboxylic acids on the stereochemical outcomes of photoallylation and photoreduction reactions of prochiral electron deficient alkenes.…”