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. 2019 Apr 16;10(19):5162-5166.
doi: 10.1039/c9sc01356c. eCollection 2019 May 21.

Photocatalytic carbanion generation - benzylation of aliphatic aldehydes to secondary alcohols

Karsten Donabauer  1 , Mitasree Maity  1 , Anna Lucia Berger  1 , Gregory S Huff  1 , Stefano Crespi  1 , Burkhard König  1
Affiliations

Photocatalytic carbanion generation - benzylation of aliphatic aldehydes to secondary alcohols

Karsten Donabauer et al. Chem Sci. .

Abstract

We present a redox-neutral method for the photocatalytic generation of carbanions. Benzylic carboxylates are photooxidized by single electron transfer; immediate CO2 extrusion and reduction of the in situ formed radical yields a carbanion capable of reacting with aliphatic aldehydes as electrophiles giving the Grignard analogous reaction product.

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Figures

Scheme 1
Scheme 1. (a) Photocatalytic carbanion generation via two consecutive SETs. (b) Redox-neutral carbanion generation followed by intramolecular SN2 reaction. (c) Envisioned catalytic cycle.
Scheme 2
Scheme 2. Isolation of 4CzIPN photo-conversion product 4CzBnBN (7a). The reaction was performed with 4CzIPN (30 μmol, 1 eq.) and 1a (4 eq.) in degassed DMA (2 mL) under a nitrogen atmosphere.
Fig. 1
Fig. 1. In situ FT-IR studies. Irradiation of a solution containing NBu4PA (5) (75 mM), 2a (75 mM) and 4CzBnBN (3.75 mM) in dry DMA lead to the formation of CO2 (2338 cm–1) and the depletion of 2a (1722 cm–1).
Scheme 3
Scheme 3. Experiments supporting the formation of a reactive anionic intermediate.
Scheme 4
Scheme 4. Proposed mechanism.
See this image and copyright information in PMC

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