Abstract
Photoreactions of acetonitrile solutions of 3,3-diaryl-1,1-dicyano-2-methylprop-1-enes (1a–c) with allyltrimethylsilane (2) in the presence of phenanthrene as a photoredox catalyst and acetic acid as a proton source formed photoallylation (3) and photoreduction (4) products via photoinduced electron transfer pathways. When (S)-mandelic acid was used as the proton source, the reactions proceeded with 3.4 and 4.8 %ee for formation of 3 and 4, respectively. The results of studies of the effect of aryl ring substituents and several chiral carboxylic acids suggested that the enantioselectivities of the reactions are governed by steric controlled proton transfer in intermediate complexes formed by π-π and OH-π interactions of anion radicals derived from 1a–c and chiral carboxylic acids.
Highlights
Coupling reactions proceeding through photoinduced electron transfer (PET) pathways have been extensively studied from both a synthetic as well as a mechanistic viewpoint [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
(S)-mandelic acid 13 and the results showed that the
CH3 CN (8 mL) solutions of a 3,3-diaryl-1,1-dicyano-2-methylprop-2-ene (1a–c, 0.14 mmol), allyltrimethylsilane (2, 0.42 mmol), phenanthrene (0.07 mmol), and CH3 COOH (1 mL) or a chiral carboxylic acid (0.14 mmol) in Pyrex vessels were degassed by argon bubbling for 5 min and the vessels were sealed
Summary
Coupling reactions proceeding through photoinduced electron transfer (PET) pathways have been extensively studied from both a synthetic as well as a mechanistic viewpoint [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. We have previously developed photoallylation and photoreduction reactions of electron deficient alkenes with allyltrimethylsilane that occur via PET pathways [22,23,24]. The current study was aimed at the development of enantioselective PET promoted coupling reactions, and at assessing the effect of chiral carboxylic acids on the stereochemical outcomes of photoallylation and photoreduction reactions of prochiral electron deficient alkenes. The results showed that these processes took place with maximum 3.4–4.8 %ee when (S)-mandelic acid was used as the chiral proton source
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