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Curtius Rearrangement Reactions of 3-(4-Azidocarbonyl) Phenylsydnone

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Curtius Rearrangement Reactions of 3-(4-Azidocarbonyl) Phenylsydnone J. Chem. Sci., Vol. 118, No. 3, May 2006, pp. 249–256. © Indian Academy of Sciences. Curtius rearrangement reactions of 3-(4-azidocarbonyl) phenylsydnone. Synthesis of 4-(sydnon-3-yl) phenyl carbamates, N-aryl-N¢-[4-(sydnon-3-yl)] phenyl ureas and their antimicrobial and insecticidal activities P R LATTHEa, P S SHINGEa,+, BHARATI V BADAMIa,*, P B PATILb and S N HOLIHOSURb,* aDepartment of Chemistry, and bDepartment of Zoology, Karnatak University, Dharwad 580 003 +Present address: Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012 e-mail: [email protected] MS received 1 September 2005; revised 4 January 2006 Abstract. 3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenyl- sydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding car- bamates (3a–h), 4,4¢-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a–l). Compounds (5a–l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a–l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a–l). All these compounds exhi- bited moderate antimicrobial activity against the few microbes tested. The carbamates have been found to be more toxic against fourth instar larvae of Aedes aegypti, in particular, the n-butyl derivative (3e). Keywords. 3-(4-Azidocarbonyl)phenylsydnone; Curtius rearrangement; 4-(sydnon-3-yl)phenyl carba- mates; N-aryl-N¢-[4-(sydnon-3-yl)] phenyl ureas. 1. Introduction 2. Results and discussion Synthesis and biological properties of sydnone deri- In this paper we report the synthesis and biological vatives incorporated with biologically active hetero- properties of some carbamates (3a–h) and ureas (4, cycles have been reported from this laboratory for 5a–l, 6a–l and 7a–l) incorporated with the sydnone the past several years.1–4 Though many of these ring, using the well-known Curtius rearrangement.10 compounds showed promising pharmacological 3-(4-Hydrazinocarbonyl)phenylsydnone (1) used as the properties at the preliminary testing, none of them starting material is converted to the acylazide de- have exhibited sufficient activity to justify further rivative (2), which when subjected to Curtius rear- screening. Hence, much needs to be done in the rangement with alcohols, water and aromatic amines, form of synthesis and screening of many more de- affords the carbamates (3a–h), symmetrical urea (4) rivatives, before we can conclude anything definite and ureas (5a–l) respectively. about structural modifications and pharmacological 3-(4-Hydrazinocarbonyl)phenylsydnone (1) on nitro- properties. So, it was thought of interest to synthe- sation with sodium nitrite gives 3-(4-azidocarbonyl) sise some more sydnone derivatives containing other phenylsydnone (2) in 75% yield. IR analysis of this biologically potent moieties. In view of the diverse compound shows a strong band at 2184 cm–1 for the and remarkable biological properties of several het- azide group stretching vibration. The 1H-NMR erocyclic systems with pendant carbamates5,6 and (300 MHz) spectrum shows two doublets at d 7×95 diphenylureas7,9 we thought of coupling these moie- (2H, J = 8×1 Hz) and d 7×83 (2H, J = 8×1 Hz) as- ties with sydnones. signed to the aromatic protons and a singlet at d 7×69 due to the sydnone CH. This compound is suffi- ciently pure for further use in rearrangement reac- *For correspondence tions. Compound (2) undergoes Curtius rearrangement 249 250 P R Latthe et al O O H H H O C NaNO2/HCl C R-OH H N NHNH2 N N3 N N C O R 0-5oC O N N Reflux O N O O O O 1 2 3a-h Benzene/H20 R1 Dry Toluene o 120 C Reflux NH2 H H H H R1 H H N N H N N N N N + N O N O N - O O O O O O 4 5a-l 0 i) Br2 in Ac2O at 0-5 C ii) 60 0C H H 1 1 R H H R O O N N N N N2H4.H2O N N O N O H2N N N O Ethanol CH3 CH3 6a-l 7a-l 1 1 3a R=Me 5a, 6a, 7a R =H 5i, 6i, 7i R =3- NO2 1 1 3b R=Et 5b, 6b, 7b R =2-Me 5j, 6j, 7j R =4- NO2 1 1 3c R=Pr 5c, 6c, 7c R =4-Me 5k, 6k, 7k R =2-OCH3 1 1 3d R=i-Pr 5d, 6d, 7d R =2-Cl 5l, 6l, 7l R =4-OCH3 3e R=n-Bu 5e, 6e, 7e R1=4- Cl 1 3f R=t-Bu 5f, 6f, 7f R =4- COCH3 3g R=2-methoxyethyl 5g, 6g, 7g R1=4- COOH 1 3h R=2-ethoxyethyl 5h, 6h, 7h R =2-NO2 Scheme 1. in boiling ethanol to afford the carbamate (3b) in In another reaction, 3-(4-azidocarbonyl)phenyl- good yield (80%) (scheme 1). The absence of an sydnone (2) on refluxing with water also underwent –1 azide band at 2184 cm and the presence of a nN–H Curtius rearrangement to give the symmetrical urea, band at 3246 cm–1 in its IR spectrum is evidence for 4,4¢-(sydnone-3-yl) diphenyl urea (4) (scheme 1). the rearrangement of azide to carbamate. This is fur- The IR spectrum of this compound shows broad 1 –1 –1 ther substantiated by the H-NMR (300 MHz) spec- bands at 3353 cm and 3125 cm due to nN–H and trum, which shows signals at d 10×15 (s, 1H, NH nC–H of sydnone respectively. The nC=O of sydnone –1 D2O exchanged), d 7×85 (d, 2H Ar-H), d 7×71 (d, 2H and amide appear as sharp bands at 1759 cm and Ar-H), d 7×61 (s, 1H sydnone C–H), d 4×28 (q, 2H, 1705 cm–1 respectively. The 1H-NMR spectrum CH2) and d 1×3 (t, 3H CH3). This is further confir- shows signals at d 9×51 (s, 2H, NH D2O exchanged), med by its mass spectrum that shows molecular ion d 7×85 (d, 4H Ar-H), d 7×71 (d, 4H Ar-H), d 7×61(s, peak m/z at 249, which agrees with the molecular 2H sydnone C–H) indicating magnetic equivalency weight of the compound. A series of carbamates (3a– of protons in both halves of the molecule. h) were prepared using different alcohols. All these Another Curtius rearrangement of 3-(4-azido- compounds were characterized by their spectral data. carbonyl)phenylsydnone (2) in presence of various Curtius rearrangement reactions of 3-(4-azidocarbonyl)phenylsydnone 251 aromatic amines gives the corresponding N-aryl-N¢- spectra of compounds (7a–l) are characterized by [4-(sydnon-3-yl)phenyl] ureas (5a–l) (scheme 1). the presence of two new bands at 3325 cm–1 and –1 –1 The IR spectra of all these compounds shows two 3214 cm for nNH2 and a sharp band at 1713 cm for –1 –1 sharp bands at 3357 cm and 3125 cm due to nN–H the nC=O. This lowering of the carbonyl frequency –1 –1 and nC–H of sydnone respectively. The nC=O of syd- from 1787 cm to 1713 cm confirms the ring –1 none and amide appears as sharp bands at 1739 cm transformation. The amide nC=O is now observed at –1 –1 and 1701 cm respectively. The absence of the azide 1635 cm , perhaps due to intermolecular H-bonding band at 2184 cm–1 also confirms the formation of with the amino group. 1H-NMR spectrum (com- 1 compounds (5a–l). The H-NMR spectrum (com- pound 7l) shows signals at d 10×23 (s, 1H, NH D2O pound 5l) shows signals at d 9×20 (s, 1H, NH D2O exchanged), d 10×05 (s, 1H, NH attached to the aryl exchanged), d 8×72 (s, 1H, NH attached to the aryl ring, D2O exchanged). The aromatic protons reso- ring, (D2O exchanged). The protons of the phenyl nate at d 8×05–7×11 (m, 8H) while the two singlets at ring attached to the sydnone resonate as two dou- d 5×42 and ä 2×23 are assigned to the NH2 and CH3 blets at d 7×80 (2H, J = 8×0 Hz) and d 7×70 (2H, of triazolinone. Another singlet at d 3×75 is due to J = 8×0 Hz), while the protons of methoxy phenyl the OCH3 protons. No significant changes are ob- ring are observed as two doublets at d 7×35 (2H, served in the characteristic spectral data of other de- J = 7×9 Hz) and d 6×91 (2H, J = 7×9 Hz). The syd- rivatives of all these compounds. none C–H and the OCH3 protons appear as singlets at d 7×61 and 3×75 respectively. We have obtained 3. Biological activity the X-ray crystal11 structure for one of these com- pounds, 5f. 3.1 Antimicrobial activity 12,13 Our recent reports on one-pot sydnone ring Preliminary antimicrobial testing has been carried transformation to 1,3,4-oxadiazolin-2-ones and their out by the cup-plate method. The antimicrobial acti- subsequent conversion to the 4-amino-1,2,4-triazolin- vity was carried out against two pathogenic bacteria, 3-ones prompted us to convert these newly synthe- Escherichia coli (Gram –ve) and Micrococcus luteus sized compounds to the corresponding oxadiazoli- (Gram +ve) and two fungal strains, Asperigillus ni- none and triazolinones. ger and Penicillium notatum. The reference drugs Compounds (5a–l) on reaction with bromine in used were Norfloxacin and Griseofulvin respec- acetic anhydride undergo ready one- pot ring conver- tively.
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