(Hive Bee)
05-15-04 05:30
No 507313
(Rated as: excellent)
Carbon-Heteroatom Bond-Forming Reactions Mediated by Cerium(IV) Ammonium Nitrate: An Overview
Vijay Nair, Sreeletha B. Panicker, Latha G. Nair, Tesmol G. George, Anu Augustine
Synlett 2003, No. 2, 156–165.
Abstract: As a powerful one-electron oxidant, cerium(IV) ammonium nitrate (CAN) is useful for a variety of oxidative transformations including carbon-carbon bond formation. Recent work has also demonstrated the usefulness of CAN in carbon-heteroatom bond-forming reactions. Particularly noteworthy is the effectiveness of CAN in building C–N, C–S, C–Se, C–Br, and C–I bonds. This account is aimed at creating awareness among organic chemists about such reactions with potential application in the synthesis of a variety of building blocks.
1 Introduction
2 Carbon-Carbon Bond-Forming Reactions Mediated by CAN: A Brief Outline
3 Carbon-Heteroatom Bond-Forming Reactions Mediated by CAN
3.1 Carbon-Nitrogen Bond Formation
3.2 Carbon-Sulfur Bond Formation
3.3 Carbon-Selenium Bond Formation
3.4 Carbon-Halogen Bond Formation
4 Conclusion
The best of:
I guess you all know what can such products yield after reduction.
Just two more examples:
Nitration of olefines:
R-CH=CH-R' ={ NaNO2, CAN / AcOH ; sonication}=> R-CH=CH(NO2)-R'
(imagine R="a nicely substituted benzene ring" and R'=Me and you have another direct nitration of allylbenzenes to nitrostyrenes)
Benzylic bromination:
Ar-CH3 ={NaBr, CAN / AcOH}=> Ar-CH2Br
(no need for bromine and reflux with a mercury lamp irradiation!)
+ ring iodinations, alpha iodination or bromination of ketones, alpha-azido-acetophenones from styrenes, …Furthermore, CAN is quite a common reagent and there are many other examples useful for just any bee.
“The real drug-problem is that we need more and better drugs.” – J. Ott
(Hive Bee)
05-15-04 05:56
No 507315
imagine R="a nicely substituted benzene ring" and R'=Me and you have another direct nitration of allylbenzenes to nitrostyrenes
that would be a nitration of a propenylbenzene wouldn't it? (which is good)
(Hive Bee)
05-20-04 23:20
No 508553
(Rated as: excellent)
These three papers deal with the addition of the O2N-CH2* radical on the aromatic ring yielding compounds of the type Ar-CH2NO2. The second paper was already referenced and the experimental part reported in the nice idea described in Post 461187 (psyloxy: "2,5-diMeO-benzaldehyde,an unusual synth from 14DMB", Chemistry Discourse). Read that post and you will understand what this reaction is good for. But besides that it is also interesting in the view of its similarity to the radical acetonylation described in ../rhodium /p2p.man
Nitromethylation of Aromatics with Nitromethane-Manganese(III) Acetate
Michael E. Kurz and Tsu-yu R. Chen
J. Org. Chem., 43(2) (1978) 239-242.
Abstract: Manganese(III) acetate was found to effect aromatic substitution by a nitromethyl group when reacted with an aromatic and nitromethane in acetic acid. Based on similarities to previously studied maganese(III) acetate systems, a mechanism involving the generation of and substitution by nitromethyl radicals is proposed. The partial rate factors, p value (vs. p+) of -1.1, and the failure to substitute on nitrobenzene suggest that the nitromethyl radical exhibits appreciable electrophilic character. This reactioii, which proceeds in a clean, reasonably high-yield manner, might well provide an alternate route to synthesizing cerlain aryl nitromethanes, which are currently made through multistep, side-chain substitutions involving alpha-halo- or alpha-cyanotoluenes.
Nitroalkylation of Aromatic Hydrocarbons Promoted by Manganese(III) Acetate
Michael E. Kurz, Preecha Ngoviwatchai, and Tosaporn Tantrarant
J. Org. Chem. 46 (1981) 4668-4672.
Abstract: Additional mechanistic and synthetic details concerning the formation of nitroalkylated aromatic products from the reaction of nitroalkanes with manganese(III) acetate and an aromatic compound are presented. A large isotope effect (ah/^d = 4.02-4.20) was found for both manganese(III)- and cerium(IV)-promoted nitromethylations with nitromethane-da while no isotope effect (ah/^d = 1-05) was observed with benzene-dg. This indicated that deprotonation (most likely from an aci radical cation) to the nitromethyl radical is the slow step while subsequent rearomatization of a o-radical complex occurs rapidly. Somewhat more convenient methods of activating the manganese(III) acetate promoter were found. However, attempts to find cooxidants or other additives which could improve this process met with only limited success. The reaction of either toluene or benzene with nitroethane or the nitropropanes and manganese(III) acetate in refluxing acetic acid gave much poorer yields (3-8%) of the corresponding nitroalkylated products. Incorporation of sodium acetate into these systems completely eliminated the aromatic substitution products and formed a-nitroalkyl acetates instead. Implications of this finding on the mechanism for the generation of nitroalkyl radicals are discussed.
Free-Radical Aromatic Nitromethylation Promoted by Cerium(IV)
Michael E. Kurz and Preecha Ngoviwatchai
J. Org. Chem. 46 (1981() 4672-4676.
Abstract: A search for metal salt oxidants, other than manganese(III) acetate, capable of effecting aromatic nitromethylation with nitromethane was undertaken. Of the many screened, cerium(IV) salts showed the most promise. Cerium(IV) ammonium nitrate gave high, though initially erratic, yields (essentially 100% yield of isomeric a-nitroxylenes from toluene and a-nitrotoluene from benzene). However, nitration products and aromatic aldehydes were generated as well. Product formation was followed as a function of time in these reactions, and nitromethylation products were shown to be converted to the corresponding isomeric tolualdehydes or benzaldehyde upon prolonged heating. Cerium(III) nitrate was shown to be primarily responsible for promoting this side reaction. Cerium(IV) acetate, generated in solution by ozonolysis of either cerium(III) nitrate or a mixture of cerium(UI) acetate and cerium(III) nitrate in acetic acid, also was shown to promote high yields of nitromethylation products. Furthermore, this reaction was free of side products. Isomer studies and relative rates for nitromethylation were determined for both cerium(IV) salts in comparison with manganese(III) acetate. A Hammett treatment in each case gave similar p values (vs. p+): -2.3 from manganese(III) acetate, -2.0 from cerium(IV) ammonium nitrate, and -1.9 from cerium(IV) acetate, indicating a common intermediate in each case. The nitromethyl radical, believed to the substituting entity, exhibits marked electrophilic properties.
This one adds a 1,3-dicarbonyl compound (dimethyl malonate) to some benzene derivatives yielding Ar-CH(COOMe)2. Even though these compounds can bee easily hydrolyzed/decarboxylated to arylacetic acids and these converted to appropriate PEA’s it is more interesting as a possibility to form various P2P’s if using ethyl acetoacetate or acetylacetone in place of dimethyl malonate (R=Me- and/or EtO-). Note that this radical reactions are performed in MeOH at room temperature as opposed to the acetonylation with Mn3+/acetone since the malonate forms a radical way easier than acetone.
Dimethyl arylmalonates from cerium(IV) ammonium nitrate promoted reactions of dimethyl malonate with aromatic compounds in methanol
Enrico Baciocchi, Donatella Dell'Aira, and Renzo Ruzziconi
Tetrahedron Letters, 27(24) (1986) 2763-2766.
Summary: Aromatic compounds undergo homolytic malonylation by reaction with cerium(IV) ammonium nitrate and dimethyl malonate in methanol at room tenperature.
The drawback of these and similar radical reactions is the need of using very large excesses of the aromatic substrate and the need of preparing Mn3+ or Ce4+ salts (though CAN is commercially available). Luckily the aromatic substrates can bee recycled by various separation methods and the remaining metal salt reoxidized and both reused.
“The real drug-problem is that we need more and better drugs.” – J. Ott
(Heavyweight Chempion(eer))
05-21-04 01:25
No 508565
I think I just came in my pants
That is a post worth a excellent rating if I ever saw one. Now, let's see about the yields.
Severe Aztecoholic and President of Sooty's fanclub - Sooty for President!!
(Hive Bee)
05-21-04 09:51
No 508618
Barium, I'm glad you enjoyed it.
But maybe it was a little too fast.
Have you seen the horrible excesses of the reactants these reactions use? Up to 20 times the molar excess in some cases!
“The real drug-problem is that we need more and better drugs.” – J. Ott
(Heavyweight Chempion(eer))
05-21-04 11:01
No 508628
I'm used to see that in the chem literature. But in most cases the reaction can be tweaked so just a little excess is needed. Usually it is just a matter of getting to know the reaction system a bit better, which solvents to use, the optimal temperature range and so on.
Severe Aztecoholic and President of Sooty's fanclub - Sooty for President!!