CS236617B1 - 2-aryl-4-acetylfuro (3,2-b) acetylfuropyrole and method of preparation - Google Patents

Abstract

The invention relates to the field of organic synthesis and deals with the preparation of new 2-aryl-4-acetylfuro[3,2-b]pyrroles. The essence of the preparation method according to the invention is that 2-aryl-4H-furo[3,2-b]pyrrole-5-carboxylic acids are heated in acetic anhydride at temperatures of 100-136°C. The compounds according to the invention are widely used as reaction components in organic synthesis. Under the conditions of the Vilsmeier reaction (DMFA + POCl3) they give 5-formylfuro[3,2-blpyrroles. Their alkaline hydrolysis leads to the formation of basic furo[3,2-b]pyrroles. In the positions of the 4,5-furo[3,2-b]pyrrole skeleton they give cycloaddition reactions, for example with dimethyl ester of acetylene dicarboxylic acid, new furo[3,2-b]azepine derivatives are formed. 2-Aryl-4-acetylfuro[3,2-b]pyrroles according to the invention are characterized by the general formula where R stands for phenyl, 4-tolyl.

Description

The invention relates to the field of organic synthesis and addresses the preparation of novel 2-aryl-4-acetylfuro[3,2-b]pyrroles.

The essence of the preparation method according to the invention is that 2-aryl-4H-furo[3,2-b]pyrrole-5-carboxylic acids are heated in acetic anhydride at temperatures of 100-136°C.

The compounds according to the invention are widely used as reaction components in organic synthesis. Under the conditions of the Vilsmeier reaction (DMFA + POCl3) they give 5-formylfuro[3,2-blpyrroles. Their alkaline hydrolysis leads to the formation of basic furo[3,2-b]pyrroles. In the positions of the 4,5-furo[3,2-b]pyrrole skeleton they give cycloaddition reactions, for example with dimethyl ester of acetylene dicarboxylic acid, new furo[3,2-b]azepine derivatives are formed.

2-Aryl-4-acetylfuro[3,2-b]pyrroles according to the invention are characterized by the general formula

COCH ₃

where

R represents phenyl, 4-tolyl.

23S617

The invention relates to 2-aryl-4-acetylfuro[3,2-b]pyrroles and a method for their preparation. A suitable method for their preparation is the decarboxylation acetylation of 2-aryl-4H-furo[3,2-b]pyrrole-5-carboxylic acids.

In general, the decarboxylation of carboxylic acids is a simple reaction that can be carried out by a number of procedures. The choice of method is mainly influenced by the structure of the starting acid, its physicochemical properties, as well as the physical and chemical properties of the expected product. Most decarboxylation reactions are carried out in the liquid phase without a catalyst or in the presence of a homogeneous or solid catalyst.

In homogeneously catalyzed decarboxylation of carboxylic acids, primary, secondary and tertiary amines as well as heterocyclic nitrogen compounds have proven to be basic catalysts.

Nitrogen containing heterocyclic compounds with an NH bond, for example pyrrole, indole or carbazole, can be alkylated or acylated in the form of anion generated by their reaction with a strong base such as sodium amide, lithium hydride or organometals. Alkylations of pyrrole (Heany H. Ley J.: J. Chem. Soc. Perkin Trans I 2292 /1972/), indole (Garner E, Albisser J.: Chemistry and Industry 110 /1974/) are described in the literature. Kováč J, Ilavský D,: Collection Czech, 2949 /1980/.

A study of the literature showed that 2-aryl-4-acetylfuro[3,2-b]pyrroles were not previously prepared.

The subject of the invention are 2-aryl-4-acetylfuro(3,2-b) pyrroles of general formula I

CGCH-, i J

where

R is phenyl and 4-tolyl and a process for their preparation.

The essence of the method of preparation of 2-aryl-4-acetylfuro[3,2-b]pyrrole of the formula I consists in the fact that 2-aryl-4H-furo[3,2-b]pyrrole-5-carboxylic acid according to author's certificate No. 233 408 of the general formula II where

R has the above meaning, heated in acetic anhydride at temperatures of 100 — 136 °C.

The advantages of the method of preparing the compounds according to the invention consist, among other things, in the fact that the reaction of decarboxylation and simultaneous acetylation takes place in one step under undemanding conditions with very good yields, whereby stabilized 4-acetylfurof 3,2-b jpyrrole derivatives are obtained. The substances that are the subject of the invention are widely used as reaction components in organic synthesis. Under the conditions of the Vilsmeier reaction (DMFA + POCb) they give 5-formyl furo[3,2-b j pyrroles. Their alkaline hydrolysis leads to the formation of basic furo [3,2-b jpyr 0lov according to author's certificate no. 234 973. In the 4,5 positions of the furo [3,2-b jpyrrole skeleton they give cycloaddition reactions, for example with the dimethyl ester of acetylene dicarboxylic acid new phoro [3,2-b] azepine derivatives are formed.

The subject matter of the invention is illustrated, but not limited, by the following examples:

Example 1

2-Phenyl-4-acetylfuro[3,2-b]pyrrole

2-Phenyl-4H-furo[3,2-b]pyrrole-5-carboxylic acid (1 g, 4.4 mmol) was heated in acetic anhydride (15 mL) at reflux for 4 h. The excess acetic anhydride was distilled off. The crude product is crystallized from ethanol. 0.85 g of 86% 2-phenyl-4-acetylfuro[3,2-b]pyrrole of structural formula Ia is obtained

Compound Ia is a crystalline substance m.p. 112 degrees Celsius (ethanol)

General formula: C14H11NO2 Molecular weight: 225.25

Elementary analysis: %C %, H %N Quantity calculated: 74.65 4.92 6.22 Quantity found: 74.42 4.88 6.2 Structure of spectral compounds methods Ia was IR, UV, proven by 1H NMR.

(III

IR:

v _max (CHCb cm-i) 1702 (C = O)

UV:

in _ma: (loge) (methanol):

326 (4.22) ¹ H NMR (CDCl3):

2.53 (3H, s, CH3CO),

6.33 (1H, dd, Ce-H),

6.69 (1H, d, Cs-H),

7.45 (1H, d, C5-H),

7.2—7.75 (5H, m, Harom),

J5.6 ⁼ 3.7 Hz,

J ₂ , ₆ = 0.8 Hz.

Example 2

2* (4-Tolyl)-4-acetyl lf uro [ 3,2-b ] pyr ol (Ib)

2-(4-Tolyl)-4H-furo[3,2-b]pyrrole-5-carboxylic acid (1 g, 4.04 mmol) was heated in acetic anhydride (20 mL) at 120 degrees Celsius for 6 h. The excess acetic anhydride was distilled off and the crude product was crystallized from ethanol. 0.6 g of 62 °/o 2-(4-tolyl)-4-acetylfuro[3,2-b] pyrrole structure is obtained

of the formula Ib COCH (Ib)

Compound Ib is a crystalline substance with a melting point of 142 °C (ethanol).

General formula: C15H13NO2 Molecular weight: 239.13

Elementary analysis: /%C % H %N Quantity calculated: 75.28 5.48 5.91 Quantity found: 75.18 ' 5.46 5.86 Structure of spectral compounds methods Ib was proved by IR, UV and 1H NMR.

IR:

v _max (CHCb cm- ^-1 ):

1692 (C=O)

UV:

Vmax (logs) (methanol, nm):

323 (4.20) 1H NMR:

2.34 (3H, s, CH3-C6H4),

2.52 (3H, s, CH3CO),

6.29 (1H, dd, Ce-H),

6.85 (1H, d, CeH),

7.17 (1H, d, Cs-H),

7.12, 7.55 [4H, dd, Har[O]m),

J _s , ₆ = 3.7Hz,

J ₂ .6 = 0.8 Hz.

Spectral measurements:

Infrared spectra were measured on a spectrophotometer! SPECORD 71 IR (Carl Zeiss, Jena). Electron spectra were measured on a Spectrophotometer! UV VIS (Carl Zeiss, Jena) in the range of 200—800 nm at concentrations of 2.10 ^-5 mol. I ^-1 . ^X H NMR spectra were recorded on an 80 MHz spectrophotometer! BS 487 C TESLA. The internal standard tetramethylsilane was used in the measurement. Chemical shifts S are given in ppm.

Claims (2)

1. 2-Aryl-4-acetylfuro [3,2-b] pyrrole R is as hereinbefore defined, heated in acetic anhydride at temperatures of 100-136 ° C. where R is phenyl and 4-tolyl. 2. A process for the preparation of 2-aryl-4-acetylfuro [3,2-b] pyrrole according to claim 1, characterized in that 2-aryl-4H-fluoro [3,2-b] pyrrole-5- carboxylic acids of formula II