Photochemical Synthesis of Aldehydes in the Solid Phase

Abstract

A substituted anthraquinone (AQ), previously shown to photochemically generate benzaldehyde in methanol solution, was attached to a commercially available resin via an 11 carbon tether and an amide bond. Photolysis of the polymer-bound AQ with visible or 350 nm UV light resulted in the formation of benzaldehyde in yields of 50-55% as determined by HPLC. The phenolic positions in the polymer were then alkylated using benzyl bromide and 1-iodo-3-(4-nitrophenyl)propane in a coupling reaction with K(2)CO(3) as a base and a solution-phase proton shuttle. Photolysis of these alkylated polymers resulted in the formation of benzaldehyde (54-89%) and 3-(4-nitrophenyl)-propanal (58-67%). The yields of both aldehydes dropped considerably with subsequent realkylation and photolysis, and the polymer beads began to show signs of deterioration. This is the first time that aldehydes have been made photochemically on a solid-supported phase.

Light‐induced controlled release of fragrance aldehydes from 1‐alkoxy‐9,10‐anthraquinones for applications in functional perfumery

“…9-11 Substituted and unsubstituted citral precursors 1-5 were prepared from their corresponding hydroxyanthraquinones by etherification with geranyl bromide and potassium carbonate in 2-butanone, according to the procedure of Blankespoor et al 8 Whereas the etherification reaction proceeded well with allylic geranyl bromide, almost no reaction occurred under the same conditions when (2-bromoethyl)benzene was used as the alkylating agent, even after prolonged reaction times. Anthraquinone ethers of 2-phenylethanol (6), hexylcinnamol (7) …”

“…Based on recent publications from Brinson and Jones 7 and Blankespoor et al 8 who reported the photochemical release of aldehydes from 1-alkoxy-9,10-anthraquinones, we considered the potential use of this substrate for the light-induced controlled release of fragrance aldehydes or ketones. The precursors are ethers and should thus be stable in most of the application bases currently used.…”

“…Photoirradiation of these systems at 350 nm in a polar environment yields the corresponding anthrahydroquinones, which, in the presence of air, are converted into carbonyl compounds and 1-hydroxy-9,10-anthraquinone (Scheme 1). [7][8][9][10][11] The rate constant for the photocleavage is dependent on the substituents in the ortho position (R 1 ), which should enable fine-tuning of the release kinetics of the aldehydes or ketones.…”

Ein polymergebundenes chirales Templat für enantioselektive Photoreaktionen

“…Für die Immobilisierung an ein Polymer stehen unzählige Methoden zur Verfügung, [3] wobei sehr wichtig ist, dass die Reaktivität und Selektivität des niedermolekularen Reagenzes oder Katalysators erhalten bleiben. In der organischen Photochemie spielen immobilisierte Katalysatoren bislang keine große Rolle, [4][5][6] was nicht überrascht, da das Reagens der Photochemie per Definition das Licht ist. In Zusammenhang mit unseren Arbeiten zu enantioselektiven photochemischen Umwandlungen in Lösung, aus denen das hoch selektive chirale Komplexierungsreagens 1 [7][8][9] hervorging (Schema 1), haben wir nun auch die Immobilisierung dieses Templats an ein Polymer untersucht.…”

“…Der Einfluss der Konfiguration an C6 auf die Stereoselektivität der geplanten Photoreaktion ist gering. In der Tat beruht die Enantioselektivität ja darauf, dass 1) ein Substrat einer photochemischen Reaktion an das NHCO-Bindungsmotiv des 2-Oxo-3-azabicyclo[3.3.1]nonan-Rings andockt und dass 2) eine vollständige Differenzierung der enantiotopen Seiten des Reaktanten durch das 5,6,7, …”