Transalkoxylation of 1,3,7-triazapyrene ethers

Abstract

In previous work [1], we found that 1,3,7-triazapyrene undergoes double S N H alkoxylation by primary alcohols extremely readily in the ROH-H 2 O-KOH-K 3 Fe(CN) 6 system to give previously unreported 6,8-dialkoxy-1,3,7-triazapyrenes 1 at room temperature. These products may be considered as imino ethers, in which the C=N bond is located in a heteroaromatic ring. As in the case of esters of carboxylic acids, esters of imino acids undergo transesterification [2]. In the present work, we studied the feasibility of a similar reaction for dialkoxytriazapyrenes 1, which would expand the methods of synthesis of ethers of this heterocycle.We found that 6,8-dimethoxy-1,3,7-triazapyrene (1a) is readily converted at room temperature into diethoxy (1b, 77% yield) and dipropoxy derivatives (1c, 66% yield) by the action of excess sodium ethylate or sodium propylate in the corresponding absolute alcohol. However, the reconversion of 1b into 1a in the MeONa-MeOH system under the same conditions proceeds but is not complete even after 48 h. This finding is attributed to the insufficient solubility of substrate 1b in absolute methanol. Using acetonitrile as a cosolvent permits carrying out this reaction in only 4 h. As subsequently found, the use of absolute solvents is not necessary. The transalkoxylation of 6,8-dialkoxy-1,3,7-triazapyrenes proceeds readily at room temperature in the R 1 OH-MeCN-NaOH system (Table 1). N N N OR RO N N N OR 1 R 1 O R 1 OH, MeCN NaOH 1a,b,d 1a-dThus, 6,8-diethoxy-1,3,7-triazapyrene (1b) was obtained from dimethoxy derivative 1a in 85% yield. The reverse reaction proceeds to give 1a in 95% yield. 6,8-Dibutoxy-1,3,7-triazapyrene (1d) could not be obtained by the direct alkoxylation of 1,3,7-triazapyrene but was synthesized for the first time by the action of 1-butanol on 6,8-dimethoxy-1,3,7-triazapyrene (1a).

Ureas as a New Nucleophilic Reagents for SNAr Amination and Carbamoyl Amination Reactions in 1,3,7‐Triazapyrene Series

“…The transalkoxylation reaction proceeds according to the mechanism of a reversible nucleophilic ipso substitution; the equilibrium shifts to the right with a large excess of the nucleophile . Thus, the system ethyl carbamate/NaH in DMSO is a source of alkoxide anions.…”

“…In our opinion, unlike urea, carbamate anion is unstable and eliminates the ethoxide anion to form isocyanuric acid. The ethoxide anion as reagent undergoes then known for these compounds transalkoxylation reaction , leading to diethoxy derivative 1b (Scheme ).…”

“…Starting compounds 1a , 1b , 1c , 1e , 1d , and 1j were obtained by known procedures; protocols for the syntheses of compounds 1f , 1g , 1h , 1i are in the succeeding text. Sodium hydride as a 60% w/w dispersion in mineral oil was used as such (Merck KGaA, Darmstadt, Germany).…”

Synthesis and cleavage of 1,3,7-triazapyrene ethers

“…Against this background, our previous observations of the easy ONSH alkoxylation [8,9], amination [10], and alkylamination [11] of 1,3,7-triazapyrenes is of great interest. Thus, the oxidative alkoxylation of 1,3,7-triazapyrene (1a) and its 2-methyl derivative 1b occurs at room temperature in the corresponding aqueous alcoholic solutions with an excess of KOH and K 3 Fe(CN) 6 [8], whereas compounds 1a and 1b remain unchanged in the conditions mentioned above [6].…”

“…Thus, the reaction of 1,3-dimethyllumazine with N-bromosuccinamide in the corresponding primary alcohol led to 6-alkoxy-and 6,7-dialkoxy derivatives of 1,3-dimethyllumazine [6]. Methoxylation of 2-nitro-5,10,15,20-tetraphenylporphyrin copper complex with sodium methoxide in DMF is reported in paper [7].Against this background, our previous observations of the easy ONSH alkoxylation [8,9], amination [10], and alkylamination [11] of 1,3,7-triazapyrenes is of great interest. Thus, the oxidative alkoxylation of 1,3,7-triazapyrene (1a) and its 2-methyl derivative 1b occurs at room temperature in the corresponding aqueous alcoholic solutions with an excess of KOH and K 3 Fe(CN) 6 [8], whereas compounds 1a and 1b remain unchanged in the conditions mentioned above [6].…”