Ketones undergo Î±-oximation by NOCl formed in situ from Me3SiCl and isoamyl nitrite, either in solution or under solvent-free conditions, to produce 1,2-dione monooximes in excellent yields. The oximation is regiospecific in appropriate cases. Â© 2003 Published by Elsevier Science Ltd

Mohammed, A.H.A.

Nagendrappa, G.

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TETRAHEDRONLETTERSTetrahedron Letters 44 (2003) 2753–2755PergamonA remarkably simple -oximation of ketones to 1,2-dionemonooximes using the chlorotrimethylsilane–isoamyl nitritecombinationAbdulkarim H. A. Mohammed† and Gopalpur Nagendrappa*Department of Chemistry, Bangalore University (Central College Campus), Bangalore 560001, IndiaReceived 18 November 2002; revised 15 January 2003; accepted 24 January 2003Abstract—Ketones undergo -oximation by NOCl formed in situ from Me3SiCl and isoamyl nitrite, either in solution or undersolvent-free conditions, to produce 1,2-dione monooximes in excellent yields. The oximation is regiospecific in appropriate cases.© 2003 Published by Elsevier Science Ltd.R3SiX reagents, according to Fleming’s analysis, reactanalogously to, but more selectively than HX.1,2 Treat-ing chlorotrimethylsilane (TMSCl) with isoamyl nitrite(AmONO) is an effective method for the in situ genera-tion of NOCl in aprotic solvent media as well as undersolvent free conditions. We have shown earlier thatNOCl thus produced adds to vinylsilanes in a regiospe-cific and stereoselective manner.3 This, to our knowl-edge, is the most convenient method for the generationand reaction of NOCl particularly for laboratory scalepreparations. Conventional procedures for obtainingNOCl under anhydrous condition are rathercumbersome.4The direct -oximation of ketones, esters, and alde-hydes by NOCl is known.4a Rasmussen and Hassnerargue that the methods used are associated with manyshortcomings and showed that silylenol ethers are supe-rior for achieving better yields and selectivity.5,6 How-ever, the handling of silylenol ethers needs special care,and their preparation is an avoidable extra step. There-fore, earlier procedures are preferred even now for thepreparation of -oximino ketones.7-Oximino ketones find many applications. They areused as starting compounds for the synthesis of imida-zoles,7 oxazoles,8 -amino acids and esters,4 -aminoalcohols,9 pharmaceutically useful heterocycles10 likeluciferin analogues,11 and other valuable products.12There is much patent literature describing the prepara-tion of -oximino ketones and their conversion todioximes. -Oximino ketones hydrolyze to syntheticallyTable 1. -Oxidation of ketones using TMSCl–AmONOKeywords : oximation; TMSCl; amyl nitrite; 1,2-diketone monooxime;NOCl.* Corresponding author. E-mail: nagendrappa@vsnl.net† On leave from Sana’a University, Sana’a, Yemen.0040-4039/03/$ - see front matter © 2003 Published by Elsevier Science Ltd.doi:10.1016/S0040-4039(03)00248-XA. H. A. Mohammed, G. Nagendrappa / Tetrahedron Letters 44 (2003) 2753–27552754Scheme 1.important -diketones,13 and serve as ligands for transi-tion metal complexes.14We have found that ketones undergo -oximation read-ily on treatment with TMSCl and AmONO in solventsor under solvent-free conditions. The results arereported.-Oximation was carried out with aryl alkyl ketones1–6, alkyl ketones 7–9, and the cyclic ketone 10. Onemolar equivalent of TMSCl was added to the substrate(either neat or in CH2Cl2 solution) at −20°C, followedby the dropwise addition of an equivalent quantity ofisoamyl nitrite. The reaction was found to be instanta-neous, but the mixture was stirred for an additionalperiod of 30 min before working up. The products werepurified on a silica gel column using 5% ethyl acetate inpetroleum ether (bp 45–55°C) as eluant, and identifiedby their mp, IR, 1H and 13C NMR spectra, which werecompared with literature data. The -ketooxime 18,because of its reduced stability, was isolated as adioxime by reacting with NH2OH·HCl. The results aregiven in Table 1.The reactions run in the absence of solvent were foundto give slightly better yields (about 2–5% more) thanthose from reactions run in solution. This observationmakes the procedure particularly attractive because ofits eco-friendly character.15The oximation is brought about by NOCl formed insitu as shown previously by the reaction of Me3SiClwith isoamyl nitrite.3 It is to be noted that only one-position of the ketones 7–10 is oximated, though bothare susceptible, and that monooximation occursregiospecifically in 7 and 9 on the more readily enoliz-able -position. This indicates that the reaction startswith enolization (facilitated by TMSCl/HCl), and fol-lows the route depicted in Scheme 1.In conclusion, -ketooximes can be prepared fromketones in a very simple manner. The reaction can berun on preparative scale.16 No extra precaution wasneeded except to avoid the entry of moisture. This workdiscloses a new application of the organsilicon reagent,Me3SiCl, for an important organic transformation.AcknowledgementsA.H.A.M. thanks ICCR, New Delhi, for a fellowshipunder Cultural Exchange Programme. The work waspartly supported by UGC-DRS and UGC-COSISTprogrammes, New Delhi. Some equipment used for thework is a donation to G.N. by the Alexander vonHumboldt Foundation, Germany.References1. Fleming, I. Chem. Soc. Rev. 1981, 10, 83.2. For excellent reviews on silicon-based reagents, see: (a)Brook, M. A. Silicon in Organic, Organometallic, andPolymer Chemistry ; Wiley: New York, 2000; p. 189; (b)Colvin, E. W. Recent Synthetic Applications of OrganoSilicon Compounds ; Rappoport, Z.; Apeloig, Y., Ed.;Wiley: New York, 1988; Vol. 2, Chapter 28, p. 1667.3. Mallya, M. N.; Nagendrappa, G.; Prasad, J. S.; Sridhar,M. A.; Lokanath, M. K.; Begum, N. S. Tetrahedron Lett.2001, 42, 2565.4. (a) Touster, O. Org. React. 1953, 7, 327; (b) Hassner, A.;Heathcock, C. J. Org. Chem. 1964, 29, 1350.5. Rasmussen, J. K.; Hassner, A. J. Org. Chem. 1974, 39,2558.6. It is claimed that a general method using t-butyl thioni-trate has been developed. It seems, however, to applyonly to microscale preparations, since preparative TLCwas used for product separation. See: Kim, Y. H.; Park,Y. J.; Kim, K. Tetrahedron Lett. 1989, 30, 2833.7. (a) Jiang, L.; Davison, A.; Tennant, G.; Ramage, R.Tetrahedron 1998, 54, 14233. They have preparedPhCOCHNOH from PhCOCH3 (40% yield) andPhCOCH(NOH)CH3 from PhCOCH2CH3 by old meth-ods; (b) Hossbach, R.; Lettau, H.; Nuhn, P.; Schneider,R.; Stenger, P.; Stiebitz, B. Pharmazie 1991, 46, 412.8. Kauffman, J. M.; Litak, P. T.; Adams, J. K.; Henry, R.A.; Hollins, R. A. J. Heterocycl. Chem. 1992, 29, 1245.9. (a) Tillyer, R. D.; Baudreau, C.; Tschaen, D.; Dolling,U.-H.; Reider, P. J. Tetrahedron Lett. 1995, 36, 4337; (b)Masui, M.; Shioiri, T. Tetrahedron Lett. 1998, 39, 5195;(c) Shimzu, M.; Tsukomoto, K.; Matsutani, T.; Fujisawa,T. Tetrahedron 1998, 54, 10265.10. (a) Canpillo, N.; Garcia, C.; Goya, P.; Paez, J. A.;Carrasco, E.; Grau, M. J. Med. Chem. 1999, 42, 1698; (b)Fro¨hlich, L. G.; Kotsonis, P.; Traub, H.; Tagavi-Moghadam, S.; Al-Masoudi, M.; Hofmann, H.; Strobel,H.; Matter, H.; Pfleiderer, W.; Schmidt, H. H. H. W. J.Med. Chem. 1999, 42, 4108; (c) DeMeester, J. W. G.; Vandel Plas, H. C.; Middelhoven, W. J. J. Heterocycl. Chem.1987, 24, 441; (d) Mendoza, J. S.; Jagdmann, G. E., Jr.;Gosnell, P. A. Bioorg. Med. Chem. Lett. 1995, 5, 2211; (e)Balsamo, A.; Breschi, M. C.; Lapucci, A.; Macchia, B.;Martinotti, E.; Nencetti, S.; Nieri, P.; Orlandini, E. J.Med. Chem. 1989, 32, 856.A. H. A. Mohammed, G. Nagendrappa / Tetrahedron Letters 44 (2003) 2753–2755 275511. Usami, K.; Isobe, M. Tetrahedron 1996, 52, 12061.12. (a) Moorhoff, C. M.; Paquette, L. A. J. Org. Chem. 1991,56, 703; (b) Katrook, M.; Ohno, M. Bull. Chem. Soc. Jpn.1973, 46, 3474; (c) Boulet, C. A.; Hanseu, A. S. Phosphorus,Sulphur, Silicon Related Elements 1991, 57, 147; (d) Yates,P.; Wong, J.; McLean, S. Tetrahedron 1981, 37, 3357.13. For -diketones, see: Lee, J. C.; Park, H. J.; Park, J. Y.Tetrahedron Lett. 2002, 43, 5661 and references citedtherein.14. (a) Basett, J.; Bensted, J.; Grzeskowial, R. J. Chem. Soc.A 1969, 2873; (b) Thakkas, N. V.; Bootwala, S. Z. IndianJ. Chem., Sect. A 1995, 34A, 370; (c) Agarwal, S. K.; Jain,J.; Chand, S. Asian J. Chem. 2002, 14, 489; (d) Frederick-son, M.; Grigg, R.; Thornson-Pett, M.; Redpath, J. Tetra-hedron Lett. 1997, 38, 7777.15. Tanaka, K.; Toda, F. Chem. Rev. 2000, 100, 1025.16. The reaction was run using 0.10–10.0 g of the ketone withno significant change either in yield or purity of theoximino ketone. Typical experimental procedure: Me3SiCl(1.2 g, 11.0 mmol) was added slowly to the ketone in 5 mLof CH2Cl2 at −20°C in a 50 mL two-necked flask fitted witha CaCl2 guard tube, followed by dry isoamyl nitrite (1.4g, 12.0 mmol). The mixture turned blue and then yellow.After stirring for 30 min more, ether or CH2Cl2 (20 mL)was added and the reaction worked up in the usual way.The product was eluted on a silica gel column using pet.ether (bp 50–55°C) containing 5% ethyl acetate to get pureproduct.

A remarkably simple Î±-oximation of ketones to 1,2-dione monooximes using the chlorotrimethylsilane-isoamyl nitrite combination

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A remarkably simple Î±-oximation of ketones to 1,2-dione monooximes using the chlorotrimethylsilane-isoamyl nitrite combination

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