GOGOI , P

HAZARIKA , P

KONWAR , D

IR@NEIST - North East Institute of Science and Technology (CSIR)

Surfactant/I2/Water: An Efficient Systemfor Deprotection of Oximes and Imines toCarbonyls under Neutral Conditions inWaterPranjal Gogoi, Parasa Hazarika, and Dilip Konwar*Organic Chemistry Division, Regional Research Laboratory,Jorhat-785006, Assam, Indiadkonwar @yahoo.co.ukReceived November 5, 2004I2/surfactant/water system deprotecting oximes and iminesto the corresponding carbonyl compounds under neutralconditions in water at 25-40 °C with very high to excellentyields.In recent years, organic reactions conducted in aqueousmedia have received much attention from chemists1because of concerns about the environment.2 Therefore,organic reactions performed in aqueous media in thepresence of a homogeneous catalyst would be an idealmethodology, provided the catalyst, preferably underneutral conditions, shows high reactivity, versatility, andsolubility in water. Also, most organic reactants includingcatalysts are insoluble in water, and the surfactants, dueto their hydrophobic and hydrophilic nature,3 form mi-celles of the reactants and promote the reaction to occurin water. On the other hand, protection-deprotection offunctional groups is a common and very essential processin multistep organic syntheses.4 The carbonyl compoundsprotected by converting them to the corresponding oximesand imines are deprotected after completing the essentialtransformations to the parent carbonyl compounds byusing a number of efficient reagents in a reactionsequence. The acidic reagents used for the deprotectionare aqueous TiCl3 and acetic acid,5 nitrous acid (as wellas nitrosonium salts such as NO+, BF4-),6 HCl,7 levulinicacid,8 pyruvic acid,9 etc. The oxidizing agents involveN2O4,10 ozone,11 tert-butylhydroperoxide,12 KMnO4/alu-mina,13 etc. The metallic salts involve thallium(III)nitrate,14 chromium compounds such as chromium(II)acetate,15 chromium(VI) species such as trimethylammo-nium chlorochromate,16 chlorotrimethylsilane(chromi-um),17 pyridinium chlorochromate,18 pyridinium chloro-chromate-H2O2,19 trimethylsilyl chlorochromate,20 bis(tri-methylsilyl) chromate,21 supported and unsupportedchromium trioxide,22 and polymer supported CrO3.23 Theother reagentssbenzeneseleninic anhydride(PhSeO)2O,24NaHSO3,25 Na2S2O4,26 etc.smay be mentioned. And thesearch for better reagents still continues.13,27 However,most of the reported methods though they are efficient,are not free from drawbacks: for example, use of toxicand hazardous transition metal oxidants, i.e., Mn,13Cr,17-23 Ti,5 Th,14 and their problems associated withwaste disposal, use of strong Lewis6 and Bronsted acids,7low temperature,11,16 involvement of longer reactiontime,18 low yield of products,24 difficulties in isolating theproducts,19 and formation of over-oxidized products.12Therefore, development of a better reagent in waterunder neutral condition is desirable.In a previous communication, we reported deoxygen-ation of nitrones to the corresponding imines catalyzedby HI28 (generated from AlCl3â6H2O/NaI/H2O/CH3CN) inhydrated media. The same system was used for thedehydration of oximes to nitriles, the Beckmann rear-rangements, and the Bischler-Napieralski reactions29 inhydrated media. Recently, we reported selective oxidationof alcohols to carbonyl compounds could be achieved with(1) (a) Grieco, P. A., Ed. Organic synthesis in water; BlackieAcademic and Professional: London, UK, 1998. (b) Li, C.-J.; Chan, T.-H. Organic Reactions in Aqueous Media; John Wiley & Sons: NewYork, 1997. (c) Lindstrom, U. M. Chem. Rev. 2002, 102, 2751. (d)Kobayashi, S.; Manabe, K. Acc. Chem. Res. 2002, 35, 209.(2) Manabe, K.; Mori, Y.; Kobayaashi, S. Synlett 1999, 9, 1401.(3) Mori, Y. Micelles Theoretical and Applied; Plenum Press: NewYork and London, 1992.(4) Greene, T. W. Protective Groups in Organic Synthesis; John Wiley& Sons: New York, 1981.(5) Timms, G. H.; Wildsmith, E. Tetrahedron Lett. 1971, 195.(6) (a) Doyle, M. P.; Wierenga. W.; Zaleta, M. A. J. Org. Chem. 1972,37, 1597. (b) Doyle, M. P.; Zaleta, M. A.; Deboer, J. E.; Wierenga. W.J. Org. Chem. 1973, 38, 1663.(7) Corey, E. J.; Hopkins, P. B.; Kim, S.; Yoo, S.; Nambiar, K. P.;Falck, J. R. J. Am. Chem. Soc. 1979, 101, 7131.(8) Depuy, C. H.; Ponder, B. W. J. Am. Chem. Soc. 1959, 81, 4629.(9) Hershberg, E. B. J. Org. Chem. 1948, 13, 542.(10) Shim, S. B.; Kim, K.; Kim, Y. H. Tetrahedron Lett. 1987, 28,645.(11) Erickson, R. E.; Andrulis, P. J., Jr.; Collins, J. C.; Lungle, M.L.; Mercer, G. D. J. Org. Chem. 1969, 34, 2961.(12) Barhate, N. B.; Gajare, A. S.; Wakharkar, R. D.; Sudalai, A.Tetrahedron Lett. 1997, 38, 653.(13) Imanzadeh, G. H.; Hajipour, A. R.; Mallakpour, S. E. Synth.Commun. 2003, 33, 735.(14) McKillop, A.; Hunt, J. D.; Naylor, R. D.; Taylor, E. C. J. Am.Chem. Soc. 1971, 93, 4918.(15) Corey, E. J.; Richman, J. E. J. Am. Chem. Soc. 1970, 92, 5276.(16) Rao, C. G.; Radhakrishna, A. S.; Singh, B. B.; Bhatnager, S. P.Synthesis 1983, 808.(17) Aizpurua, J. M.; Palomo, C. Tetrahedron Lett. 1983, 24, 4367.(18) Maloney, J. R.; Lyle, R. E.; Scovedra, J. E.; Lyle, G. G. Synthesis1978, 212.(19) Drabowicz, J. Synthesis 1980, 125.(20) Aizpurua, J. M.; Juaristi, M.; Lecea, B.; Palono, C. Tetrahedron1985, 41, 2903.(21) Lee, J. G.; Kwak, K. H.; Hwang, J. P. Synth. Commun. 1992,22, 2425.(22) (a) Hamal, S.; Mahto, S. K.; Gujurel, G. L. Indian J. Chem.,Sect. B 1996, 35, 1116. (b) Pravin, M. B.; Bhushan, M. K. TetrahedronLett. 1998, 39, 5867.(23) Narayanan, N.; Balasubramaniam, T. R. J. Chem. Res., Synop.1992, 4, 132.(24) Barton, D. H. R.; Lester, D. J.; Ley, S. V. J. Chem. Soc., Chem.Commun. 1977, 445.(25) Pines, S. H.; Chemerda, J. M.; Kozlowski, M. A. J. Org. Chem.1966, 31, 3446.(26) Pojer, P. M. Aust. J. Chem. 1979, 32, 201.(27) (a) Khazaei, A.; Manash, A. A. Synthesis 2004, 1739. (b) Martin,M.; Martinez, G.; Urpi, F.; Vilarrase, J. Tetrahedron Lett. 2004, 45,5559 and references therein.(28) Boruah, M.; Konwar, D. Synlett 2001, 6, 795.(29) Boruah, M.; Konwar, D. J. Org. Chem. 2002, 67, 7138.1934 J. Org. Chem. 2005, 70, 1934-193610.1021/jo0480287 CCC: $30.25 © 2005 American Chemical SocietyPublished on Web 01/29/2005the DMSO/N2H4âH2O/I2 system in hydrated media andit was shown that I2 could be reduced by N2H4 to generateHI [in situ], and catalyze the oxidation process in thepresence of DMSO.30 Now, an alternate system for thecleavage of the CdN bond catalyzed by I2 is devised basedon the hydrophobic and hydrophilic nature of a surfac-tant, which would form micelles of I2 and oxime/iminesin water and promote the deprotection process. Althoughthe application of surfactants as a reagent in organicsynthesis is well investigated,31 to the best of ourknowledge, its use as a promoter of I2-catalyzed cleavageof the CdN bond in water under neutral conditions isnot exploited. We now first report here an efficientenvironmentally friendly catalytic system, surfactant/I2/water, for the deprotection of oximes and imines tocarbonyl compounds in water under neutral conditionsat 25-40 °C (Scheme 1).Although the reaction of oximes/imines with a catalyticamount of I2 in water did not proceed at all (due to poorsolubility of reactant and I2 in water), the addition ofsurfactant (sodium dodecyl sulfate, SDS) to the reactionmixture led to the formation of carbonyl compounds. Forexample, 1 M of oxime/imines, 0.2 M of I2, and 0.2 M ofsodium dodecyl sulfate (SDS) were mixed in water (10mL) and the reaction mixture was stirred for a stipulatedtime at 25-40 °C; after workup it produced the corre-sponding carbonyl compounds with very good to excellentyields [Table 1].We found that this system did not produce iodoxime/imidoyl iodide3232-33 or over oxidized product (acid)12 inthe reaction mixture. And it produced neither cis nortrans halogenated products when cinnamaldehyde [entry1k] or furfuryl oximes [entry 1l] were used as substrates.Both cis and trans isomers of oximes/imines were con-verted smoothly to the corresponding carbonyl com-pounds under the same reaction condition (in all casesboth cis and trans isomers of oximes/imines were usedas a mixture). The sterically less hindered ketoximes[entry 1a-e] were successfully cleaved with faster ratesto the corresponding carbonyl compounds than stericallymore hindered ketoximes. We found that the rates as wellas yields of the reactions are dependent on the substit-uents present on aryl or heteroaryl rings. The electron-donating groups such as MeO, isobutyl, and Me on thearomatic ring enhance the rate of the reaction [entry 1d,1g, and 1i]. Similarly, the aldoximes were converted tothe corresponding aryl aldehydes with excellent yields[entry 1f-n]. Also, the reagent cleaved the imines to thecorresponding carbonyl compounds without forming anyiodinated side products. The temperature range of thereaction was determined to be 25-40 °C.(30) Gogoi., P.; Sarma, G. K.; Konwar, D. J. Org. Chem. 2004, 69,5153.(31) Manabe, K.; Limura, S.; Min, X.; Kobayashi, S. J. Am. Chem.Soc. 2002, 124, 11971.(32) Patai, S., Ed.The Chemistry of Carbon-Nitrogen Double Bond;John Wiley & Sones: London, UK, 1970; p 597.(33) (a) Dictionary of Organic Compounds, 6th ed.; Chapman andHall: London, UK, 1996. (b) Donkor, I. O.; Gangjee, A.; Kisliuk, R. L.;Gaumont, Y. J. Heterocycl. Chem. 1991, 28, 1651.SCHEME 1 TABLE 1. Conversion of Oximes/Imines to CarbonylCompoundsa Isolated yield. b Stirring at 25-40 °C. c The structures of thecompounds were determined by using 1H NMR, FTIR, andelemental analyses and comparison with authentic samples.33J. Org. Chem, Vol. 70, No. 5, 2005 1935Regarding the mechanism of the reaction, it is proposedthat the surfactant promotes micelle formation fromiodine and the oxime/imine in water, in which theelectrophilic iodine activates hydration of the carbon-nitrogen double bond, possibly via an iodonium ion, thatsuffers attack by water to form carbonyl compounds andiodine in the reaction mixture [Scheme 2].In conclusion, the salient features of the reaction arethe following: (1) Iodine is an efficient catalyst in thepresence of surfactant for the regeneration of carbonylcompounds from oximes and imines. (2) The system doesnot form iodoxime/imidoyl iodide or over-oxidized prod-ucts (acids) in the reaction mixture. (3) The cleavage ofthe CdN bond can be carried out in water under neutralcondition at 25-40 °C, eliminating toxic and acidicreagents. (4) The workup procedure is simple and yieldsare good to excellent.Experimental SectionGeneral Procedure for Deprotection of Oximes to Car-bonyl Compounds. In a 50-mL round-bottom flask, iodine (0.2mmol), oxime (1 mmol), and surfactant (sodium dodecyl sulfate,0.2 mmol) in H2O (15 mL) were added with stirring at roomtemperature for 10 min, then the temperature of the reactionmixture was raised to 40 °C and kept at this temperature for astipulated time with stirring. The progress of the reaction wasmonitored by TLC. The product was extracted with diethyl ether(2  25 mL), the organic layer was washed with brine (2  15mL), dried over anhydrous Na2SO4, concentrated, and purifiedby column chromatography on SiO2 (60-120 mesh) with use ofan ethyl acetate/hexane mixture as eluent; distillation of thesolvent under reduced pressure gave carbonyl compounds.4-Methoxybenzaldehyde (3g). 4-Methoxybenzaldehyde wasprepared from 4-methoxybenzaldoxime by using the generalprocedure described above: 123 mg, (isolated yield; 90.4%) as aliquid; 1H NMR (CDCl3, 60 MHz) ä 9.87 (s, 1H), 7.83 (d, 2H),7.0(d, 2H), 3.87 (s, 3H); FTIR (CHCl3) 1684 cm-1. Anal. Calcdfor C8H8O2 (136.15): C, 70.58; H, 5.92. Found: C, 70.58; H, 5.88.Acknowledgment. The authors acknowledge theDirector, Dr. P. G. Rao, the analytical division of RRL,Jorhat, Assam, India, for their help. Also, P.G. thanksCSIR, New Delhi for a grant of JRF fellowship.Supporting Information Available: Characterizationdata including 1H NMR, FTIR, and elemental analyses of allthe compounds. This material is available free of charge viathe Internet at http://pubs.acs.org.JO0480287SCHEME 21936 J. Org. Chem., Vol. 70, No. 5, 2005

AN EFFICIENT SYSTEM FOR DEPROTECTION OF OXIMES AND IMINES TO CARBONYLS UNDER NEUTRAL CONDITIONS IN WATER

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AN EFFICIENT SYSTEM FOR DEPROTECTION OF OXIMES AND IMINES TO CARBONYLS UNDER NEUTRAL CONDITIONS IN WATER

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