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

Abstract

Diastereoselectivity in the photoallylation and photoreduction of 1,1-dicyano-2-methyl-3-phenyl-1-butene by allyltrimethylsilane in the presence of phenanthrene was dependent on the structures and stoichiometry of the added carboxylic acids. Diastereoselectivity increased up to 72% by the addition of equimolar amount of L-lactic acid based on the alkene.

Control of the Chemoselectivity of Metal N-Aryl Nitrene Reactivity: C–H Bond Amination versus Electrocyclization

“…3-Phenyl-2-butanone s7a. 15 The general procedure was followed using 2.80 g of benzyl methyl ketone (20.9 mmol), 10.4 mL of a 50% aqueous soln. of NaOH, 0.166 g of benzyltrimethylammonium chloride (0.731 mmol) and 1.94 mL of MeI (31.3 mmol).…”

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 •− .…”

“…Based on the results of molecular orbital calculations with related compounds, it is estimated that the radical contribution to radical anion 1 •– is large at the dicyano substituted carbon (α) and that negative charge density is large at the dialkyl substituted carbon (β) [23,24,26,27]. In accord with this conclusion, the photoreaction of 1a with 2 using CH 3 COOD as the additive produced mainly mono-deuteriated forms of 3a and 4a in which deuterium is present at the stereogenic carbons marked with * in Scheme 4.…”

“…Hexane and 2-propanol were distilled without using a drying agent. Allyltrimethylsilane ( 2 ) was prepared using a reported procedure [27]. Activated alumina was dried at 200 °C for 2 h before use.…”

“…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.…”