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. Author manuscript; available in PMC: 2018 Apr 12.
Published in final edited form as: J Am Chem Soc. 2018 Feb 22;140(9):3322–3330. doi: 10.1021/jacs.7b12768

Table 4.

Leaving Group Scope in the Enantioselective Spin-Center Shift-Enabled α-Benzylation of Aldehydes and Its Impact on Reactivitya

graphic file with name nihms954729u4.jpg
entry X Ered (V) Ksv(mM−1) pKa (XH) yield (2 h) yield [time] 16:49
1 OAc −1.19 0.84 4.76 75% 90% [3 h] 18
2 NMe3+Br− n.d.b 0.13 9.80 67% 86% [5 h] 14
3 OH −1.29 1.05 15.7 39% 85% [5 h] 7.7
4 OMe −1.29 1.15 15.2 29% 71% [24 h] 5.1
5 OTBDPS −1.30 0.82 ⪝13.6 20% 61% [48 h] 3.1
6 – −1.30 1.30 data for pyridine·HBr
a

Electrophile (0.25 mmol), aldehyde 13 (2.0 equiv), lutidine (50 mol %), water (30 equiv), organocatalyst 8 (20 mol %), and photocatalyst 18 (0.5 mol %) were irradiated in DMA with a 34 W blue LED lamp. Yields of 16 and 49 were determined by 1H NMR. Enantioselectivities were determined by chiral HPLC analysis following reduction of the crude aldehyde to the corresponding alcohol. Acidity data in water from ref 24. See the SI for full experimental details.

b

Low solubility prevented electrochemical measurements in aprotic solvents.