Photochemical Homologation for the Preparation of Aliphatic Aldehydes in Flow

Abstract

Cheap and readily available aqueous formaldehyde was used as a formylating reagent in a homologation reaction with nonstabilized diazo compounds, enabled by UV photolysis of bench-stable oxadiazolines in a flow photoreactor. Various aliphatic aldehydes were synthesized along with the corresponding derivatized alcohols and benzimidazoles. No transition-metal catalyst or additive was required to affect the reaction, which proceeded at room temperature in 80 min.

A General Method for Photocatalytic Decarboxylative Hydroxylation of Carboxylic Acids

“…13 C­{ 1 H} NMR (101 MHz, CDCl 3 ): δ 137.1, 132.2, 130.3, 128.6, 63.3, 38.4. Analytical data are in accordance with literature data …”

“…1 H NMR (400 MHz, CDCl 3 ): δ 7.29−7.23 (m, 2H), 7.13 (d, J = 8.4 Hz, 2H), 3.78 (t, J = 6.6 Hz, 2H), 2.79 (t, J = 6.6 Hz, 2H), 2.04 (br, 1H). 13 25 3-Phenylpropan-1-ol (2cc). The product (55.2 mg, 81% yield) was isolated using flash chromatography (40% EtOAc/PE), as a colorless oil.…”

Living with our machines: Towards a more sustainable future

“…The homologated product could be further diversified to benzimidazoles or, on reduction, to alcohols. Again these reactions provide access to materials often to obtain by more conventional [43]…”

Cyclopropanation Reactions of Semi-stabilized and Non-stabilized Diazo Compounds

“…81 A broad range of bis-alkyl diazo compounds was efficiently generated, undergoing in situ metalfree protodeboronative and oxidative C(sp 2 )-C(sp 3 ) crosscouplings. This methodology has also been used later by the same group for C-H bond-functionalization reactions, 82 the preparation of aldehydes derivatives, 83 and for threecomponent reactions. 84 The oxidation of free hydrazones has also been investigated in both batch and continuous-flow conditions.…”