Catalytic asymmetric allylation of aldehydes with alkenes through allylic C(sp3)–H functionalization mediated by organophotoredox and chiral chromium hybrid catalysis

We have developed a catalytic asymmetric nucleophilic allylation of aldehydes using simple alkenes as pronucleophiles without relying on stoichiometric metals.


OH (R)-8a
All the spectroscopic data matches with the previously reported data. S-4

OH (R)-8h
Prepared according to the general procedure, then the crude material was purified by silica gel flash column chromatography (CH 2 Cl 2 /hexane = 1/2 to 2/1, v/v) to afford (R)-8h as colorless oil (25.5 mg, 59%). All the spectroscopic data matches with the previously reported data. S-10

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Procedure for preparation of 8l and 8v

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as colorless oil along with the inseparable mixture of stereoisomers (8w) (42.8 mg, 97%). All the spectroscopic data matches with the previously reported data. 11 The following spectroscopic data were collected with a pure sample obtained by preparative TLC. 1  S-17

Procedure for preparation of 8n and 8o
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Enantiomeric excess was determined after protection of 8u by p-NO 2  8l-8v: Following the following reaction scheme, diol 12 was obtained. The absolute configuration was determined by optical rotation value of diol 12. Those of others were assigned by analogy.
8v (38 mg, 0.216 mmol, 1 eq, 83% ee) were dissolved in CH 2 Cl 2 (2 mL) in a round bottom flask. Then the flask was connected to an oxygen tank with a bubbler. The reaction mixture was cooled to -78 ºC. The ozone generator was switched on and the ozone went into the reaction flask. The reaction mixture was allowed to stir until the color changed to blue. NaBH 4 (16.8 mg, 0.431 mmol, 2 eq) and MeOH (1 ml) were added and the mixture was warmed up to room temperature. The reaction mixture was stirred for 15 h, and then quenched with saturated aq. NH 4 Cl. The organic layer was separated, and the aqueous layer was further extracted three times with AcOEt. The combined organic layer was washed with water and brine and dried over Na 2 SO 4 . After the evaporation under reduced pressure, the residue was purified by silica gel flash column chromatography (hexane/AcOEt = 3/1 to 1/1, v/v) to give the desired diol 9 (30.2 mg, 78% yield) as a colorless oil.

Optimization Study for Aliphatic Aldehydes
During the optimization of racemic reaction, DCE solvent was found to be better solvent than DCM in terms of reactivity.
Addition of MgPhPO 3 was effective for improving enantioselectivity, while the reaction rate was slower than in the presence of Mg(ClO 4 ) 2 . 48 hours was required for the completion of the reaction. S-27

Redox potentials of intermediates in catalytic cycle
We assumed that the proposed catalytic cycle ( Figure 2 in the text) is feasible based on the following redox potentials of intermediates. Although oxidation potential of cyclohexene is higher than that of excited state of photocatalyst 10, one electron transfer would be possible based on the related precedent (cyclopentene and photocatalyst 11). 15 In

TEMPO trapping experiment
To confirm the generation of an allyl radical, a radical trapping experiment by the addition of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy, free radical) was conducted. S-28