Application en série benzofurannique d'un nouveau procédé de nitration par l'acide nitrique en présence de chlorure stannique

Abstract

JACQUES EINHORN, PIERRE DEMERSEMAN ct R E N~ ROYER. Can. J. Chem. 61. 2287Chem. 61. (1983. On determine la possibilitk d'Ctcndrc en sCric benzofurannique une nouvclle tcchnique de nitration par l'ac~de nitrique, en prCscncc de chlorure stanniquc, dans Ic chlorure de methylkne. Cettc technique mirite d'Ctre retenue pour la commoditk de sa niise cn oeuvrc ct la divcrsitb dcs produits qu'elle cst susccptiblc dc fournir, selon les conditions exper~mcntales.JACQUES EINHORN, PIERRE DEMERSEMAN, and RENE ROYER. Can. J. Chem. 61, 2287Chem. 61, (1983. A new nitration technique, using nitric acid in the prcscncc of stannic chloride in dichloromethane, has been extcnded to a series of bcnzofurans. Thc ease of performing the reaction as well as the diversity of products that can bc obtained under various cxpcrimcntal conditions make it a worthwhile technique.[Journal translation]Le benzofuranne et la plupart de ses derives dont I'hCterocycle n'est pas substitue sont trop fragiles pour que leur nitration puisse Ctre effectuee avec des rendements satisfaisants dans les conditions usuelles, au moyen, par exemple, d'acide nitrique dans I'acide ou I'anhydride acetique (1 -16). Or, nous avons recemment montre que la nitration des composes aromatiques peut Ctre assuree d e fagon commode et rentable au moyen d'un complexe -C1,Sn(N02)2 -que forment l'acide nitrique et le chlorure stannique dans le chlorure de methylene (17). I1 nous a semblC inttressant de preciser dans quelle mesure cette methode pouvait Ctre etendue en serie benzofurannique, etant donne notamment la diversite et I'importance des propriCtCs biologiques des nitro-2 benzofurannes (10, 13, 18 -24)..Nous I'avons donc appliquee au benzofuranne 1 lui-mCme, ainsi qu'au methyl-2 benzofuranne 2 et, pour comparaison, au methyl-3 benzofuranne 3.Des resultats exposes sur le tableau ci-joint, il ressort que la methode en question presente les n~& m e s avantages en serie benzofurannique qu'en serie benzenique. Bien qu'elle ne convienne pas mieux que d'autres pour assurer la nitration des benzofurannes 1 et 3 non substitues en position 2, elle est parfaitement utilisable dans le cas du methyl-2 benzofuranne 2. Si, en effet, le benzofuranne 1 ne donne ainsi que des traces de nitro-2 benzofuranne 4 (2), tandis que le methyl-3 benzofuranne 3 est cornpletement dCcomposC, le methyl-2 benzofuranne 2 fournit une petite quantitC du derive nitre en 3 9 qui avait deja ttC decrit (25), cBtt d'une majorite de son isomere 10 inconnu jusqu'i present.Par ailleurs, comme un bon nombre de nitro-2 benzofurannes ont ete obtenus jusqu'ici par deplacement "ipso" d'un groupement acttyle plut6t que par substitution directe en position 2 , nous avons utilise la m&me mtthode pour traiter I'acCtyl-2 benzofuranne 5 et I'acCtylI2 trimethyl-3,5,6 benzofuranne 6 '~r t i c l e LXVIII de la sCric: "Recherches sur le benzofuranne". LVII: voir ref. 16.( 12). Nous y avons enfin soumis, a titre complementaire, I'acide coumarilique 7 et I'acide methyl-3 coumarilique 8, afin de preciser dans quelle mesure des der...

Regioselective Nitration and/or Halogenation of Iridabenzofurans through Electrophilic Substitution

“…In the case of the related organic compound 2-methylbenzo­[ b ]­furan, reaction with N -bromosuccinimide or bromine results in bromination at the 3-position, which corresponds to C6 of the iridabenzofuran 1 . However, nitration of the same organic compound with nitric acid in the presence of tin­(IV) chloride gives a mixture of 2-methyl-6-nitrobenzo­[ b ]­furan (which corresponds to nitration at the C2 position of the iridabenzofuran 1 ) and 2-methyl-3-nitrobenzo­[ b ]­furan (which corresponds to nitration at the C6 position of the iridabenzofuran 1 ) in a ratio of ca 4:1 . In practice, it has been found that the regioselectivity of the nitration of benzo­[ b ]­furans is highly dependent on the nature and position of the substituents on the fused rings, as well as the nitrating reagent employed .…”

“…10 However, nitration of the same organic compound with nitric acid in the presence of tin(IV) chloride gives a mixture of 2-methyl-6-nitrobenzo [b]furan (which corresponds to nitration at the C2 position of the iridabenzofuran 1) and 2-methyl-3-nitrobenzo [b]furan (which corresponds to nitration at the C6 position of the iridabenzofuran 1) in a ratio of ca 4:1. 11 In practice, it has been found that the regioselectivity of the nitration of benzo [b]furans is highly dependent on the nature and position of the substituents on the fused rings, as well as the nitrating reagent employed. 12 Therefore, although the f k − data successfully indicate the atoms that are susceptible to electrophilic attack, the utility of these to predict the regioselectivity of benzofuran and iridabenzofuran nitration reactions has limitations.…”

“…Although iridabenzofurans with mixed nitro and bromo substituents were not obtained through reaction of 1 or 2 with copper nitrate and lithium bromide in acetic anhydride, IrCl(C 7 H 3 O{NO 2 -2}{Br-6}{OMe-7})(PPh3) 2 (11) can be prepared by brominating the free C6 site of 4 with 1.0 equiv of pyridinium tribromide (Scheme 4). Further bromination of 11 was not observed, even when up to 5.0 equiv of pyridinium tribromide was used.…”

“…Using “Menke” conditions the cationic iridabenzofuran 1 undergoes nitration at C2 to give the mononitro derivative 3 as the only detected product. While it is noteworthy that bromination of 1 instead occurs exclusively at C6, precedent for the regioselectivities of these reactions is found in the nitration and bromination reactions of the related organic compound 2-methylbenzo­[ b ]­furan. , …”

“…Herein we report selective mono-and dinitration of these iridabenzofurans as well as the formation of iridabenzofurans with mixed nitro and halo substituents. Specifically, we report that (i) mononitration of cationic 1 (at C2 10), (iv) the nitro-substituted iridabenzofurans 3 and 5 do not react further with pyridinium tribromide but the neutral mononitro derivative IrCl(C 7 H 4 O{NO 2 -2}{OMe-7})-(PPh 3 ) 2 (4) undergoes bromination with this reagent to give IrCl(C 7 H 3 O{NO 2 -2}{Br-6}{OMe-7})(PPh 3 ) 2 (11), and (v) the single crystal X-ray structure have been determined for 3−7 and 11.…”