Cyclisation of 1-A~etylaminocinnamanilides in Presence of Aromatic Aldehydes. One-pot Synthesis of 1-Aryl-4-benzylldene-lstyryl- l·imldazolin-5-ones
| Main Authors: | ARCHANA JAIN, ARYA K. MUKHERJEE |
|---|---|
| Format: | Article Journal |
| Bahasa: | eng |
| Terbitan: |
, 1988
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/6091005 |
Daftar Isi:
- Chemistry Department, Faculty of Science , Banaras Hindu University, Varanasi-221 005 Manuscript received 22 January 1987, revised 3 September 1987, accepted 16 December 1987 accepted 16 December 1987 A CETIC acid mediated cyclisation of 2-acetylaminocinnamanilides (la) to the corresponding 2-methyl- imidazolin-5-ones (2) was reported to be unsuccessful'. In order to verify the Baldwin rules, we reinvestigated this reaction and have found that 2 (Arl =Ph) is indeed formed but it decomposes on heating. With a view to converting the thermally unstable compound 2, generated in situ, into a more stable system, we have now carried out the cyclisation of la in the presence of suitable aromatic aldehydes and have found the products to be 2-styry1- 2-imidazolin-5-ones (3). The formation of the products 3 is obviously due to the condensation of the activated methyl group of 2 with the aromatic aldehyde present in the reaction mixture. Synthesis of 3 by the cyclocondensation of lb is possible, but this would involve several steps, starting from the preparation of cinnamoylglycine. This procedure would be difficult to apply in the case of 3 carrying a free hydroxyl group, for example 3b. Also, the conversion of 1 by the reported methods,s requires very long time arid the use of Schiff basescs for obtaining 3 involves additional step. The present one-pot synthesis overcomes these difficulties. The starting materials are easily available and the reaction is quite fast. The products were characterised by spectral data and elemental analyses. The alternative structure 4 is ruled out on the basis of 1I1 nmr spectra in which the signal for a methyl group is not discernible and two doublets near the aro-matic region with coupling constants of 14 Hz (Table 1) accounts for the (Z)-configuration of the styryl moiety. The anilides (la) used were the authentic (z)-isomers which would cyclise to the corresponding (Z)-4-benzylidene-2-methyl-2-imidazolin-5-one (2) which in turn would react with the aldehydes to give 3. It should be emphasised that on steric consideration the (Z)-compound 2 is more stable than its (E)-isomer and there is no question of its undergoing isomerisation during heating. Thus, the configuration of the olefinic centre at 4-position of 3 is (Z),