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Synthesis 2010(10): 1712-1718  
DOI: 10.1055/s-0029-1218709
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Oxidation and Deprotection of Primary Benzylamines by Visible Light Flavin Photocatalysis

Robert Lechner, Burkhard König*
Institute of Organic Chemistry, University of Regensburg, Universitätsstr. 31, 93040 Regensburg, Germany
Fax: +49(941)9431717; e-Mail: burkhard.koenig@chemie.uni-regenburg.de;
Further Information

Publication History

Received 1 February 2010
Publication Date:
26 March 2010 (online)

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Abstract

We report a photocatalytic oxidation procedure that can be used to convert benzylamines into their corresponding aldehydes under mild conditions without over-oxidation, using riboflavin tetraacetate as photocatalyst and blue emitting LEDs (440 nm) as light source. Oxygen is the terminal oxidant and H2O2 and NH3 appear as the only byproducts of the oxidation of primary benzylamines. Furthermore, we have developed a photocatalytic protocol for 4-methoxybenzyl (Mob) group deprotection of primary amines and alcohols. Double bonds, benzyl-protected esters and alcohols are tolerated under the applied conditions, whereas the deprotection of protected secondary amines is not applicable. Mob-protected carboxylic acids and carboxybenzoyl (Cbz) protected amines are inert under the photodeprotection conditions.

Key words

flavin - photooxidation - redox chemistry - electron transfer - benzyl protecting group

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13

It was shown in individual experiments that the photostability of RFT was enhanced under acidic conditions. The increased stability of RFT may result from protonation of the substrate, protonation of deprotected products or protonation of RFT in the excited state.

14

The distance between the reaction flask and the LED array was about 1 cm. The reaction mixture was heated by the intense irradiation to about 40 ˚C.