Synthesis of 4-(4-methoxyphenyl)-2,6-dinitrobenzaldehyde

Abstract

Photoacid generators capable of undergoing decomposition under irradiation with visible light are very important for efficient oligonucleotide microarray fabrication. In this case, there are no detrimental effect of UV irradiation on growing oligonucleotide chain and related side reactions leading to degradation of targeted oligonucleotides [1, 2]. An important intermediate product in the synthesis of photoacids necessary for the preparation of oligonucleotide bioarrays is 4-(4-methoxyphenyl)-2,6-dinitrobenzaldehyde, which was previously synthesized by oxidation of 2-bromomethyl-5(4-methoxyphenyl)-1,3-dinitrobenzene (I) with bis(tetrabutylammonium) dichromate on prolonged heating in boiling chloroform; however, the yield of II was as poor as 23% [2]. The goal of the present work was to develop a procedure which could be the most convenient for the preparation of 4-(4-methoxyphenyl)2,6-dinitrobenzaldehyde. The transformation of benzyl halides into the corresponding aldehydes is widely used in synthetic organic chemistry [3–5]. Benzyl halides can be converted into aldehydes via oxidation according to Kornblum [4]. However, the Kornblum oxidation of benzyl bromide I in DMSO in the presence of NaHCO3 (Scheme 1) gave a mixture of aldehyde II and alcohol III at a ratio of ~2 : 1 (cf. [6]). By oxidation of that mixture with pyridinium chlorochromate (PCC) in methylene chloride we succeeded in obtaining aldehyde II in 90% yield. Variation of the reaction conditions made it possible to synthesize alcohol III in 94% yield from compound I, and the subsequent oxidation of III with PCC quantitatively afforded aldehyde II. In addition, benzyl halides can be converted into aldehydes according to Krohnke [5]. The reaction of pyridinium salt IV with N,N-dimethyl-4-nitrosoaniline hydrochloride and subsequent hydrolysis of Schiff ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 7, pp. 1089–1091. © Pleiades Publishing, Ltd., 2013. Original Russian Text © E.B. Nikolaenkova, I.A. Os’kina, V.A. Savel’ev, V.A. Samsonov, A.Ya. Tikhonov, V.A. Ryabinin, A.N. Sinyakov, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 7, pp. 1103–1105.