Notizen
961
Montmorillonite K-10 as Highly Efficient and Mild Catalyst for Deprotection of Ketone Dimethylhydrazones Using Microwaves in a Solventless System Rahmam Hosseinzadeha, Ali Sharifib, Mojtaba Mirzaeib, and Kourosh Tabar Heydarb a
b
Department of Chemistry, Mazandaran University, Babolsar, Iran. Chemistry & Chemical Engineering Research Center of Iran, Tehran, Iran
Considering, the usefulness of microwave heating in activating a wide variety of organic reactions is now well established [12]. Besides, the importance of surface active catalysts is becoming more significant, because of their enhanced selectivity and the use of milder reaction conditions compared to conventional ones [13]. We wish to report herein a solventless system for regeneration of ketones from dimethylhydrazones using montmorillonite K-10 under microwave irradiation.
Reprint requests to Dr. R. Hosseinzadeh. E-mail:
[email protected]
Results and Discussion
Z. Naturforsch. 57 b, 961Ð962 (2002); received March 19, 2002
Montmorillonite K-10 [14] is non-toxic powder, which can be filtered easily from the process and may be reused after activation. The reaction proceeds efficiently in high yields at ambient pressure in a short time (two minutes) and without involvement of toxic and expensive material. The results of the deprotection reactions are summarized in Table 1. For example, when acetophenone dimethylhydrazone (1a) was treated with montmorillonite K-10 under microwave irradiation acetophenone (2a) was obtained in quantitative yield (entry 1). However, when 1a irradiated in solid state (mixed with SiO2 or Al2O3 instead of montmorrilonite K-10) in the same condition or in a solvent (H2O or DMF) the corresponding ketone 2a was obtained in much lower yield (entries 2Ð5). The cleavage of other acyclic or cyclic ketone dimethylhydrazones 1bÐh with montmorillonite K-10 proceeded easily with good yields (entries 6Ð12). In conclusion, the present results demonstrate that montmorillonite K-10 serves as efficient, rapid, mild, and inexpensive reagent to regenerate ketones from corresponding dimethylhyrazones under microwave irradiation. The superiority of this method over the existing methods coupled with the ease of operation, the simplicity of workup, and the environmental advantage makes the process very useful.
Dimethylhydrazones, Microwave
Montmorillonite
K-10,
N,N-Dimethylhydrazones of ketones were efficiently and rapidly deprotected to the corresponding ketones by Montmorillonite K-10 clay using microwave irradiation under solvent free conditions.
Introduction Hydrazones have been found to be one of the most useful synthetic precursors of aldehydes and ketones [1]. In this method, a key point is the cleavage of the hydrazone moiety to the carbonyl group. Previously, a variety of such methods have been reported, including oxidative cleavage by ozone [2], singlet oxygen [3], NaIO4 [4], dimethyldioxirane [5], or hydrolytic cleavage by oxalic acid [6], salt method [7], BF3 · OEt2 [8] and catalytic method using bismuth [9], palladium [10] and copper catalyzed hydrolysis [11] catalysis. Some of these procedures suffer from one or more drawbacks: use of a heavy metal, toxic solvent or reagent which not ideal from an environment point of view, long reaction times, difficulties in isolation of products, and also expensive or potentially explosive reagents under condition of excessive heating. The ozonolysis method provides nearly quantitative chemical yield under neutral conditions and short reaction times, but this method can not be used if there are other ozone-sensitive groups such as alkenes in the molecule. Therefore in this context introduction of new methods with environmental consciousness using inexpensive reagents for such functional group transformations is desirable. 0932Ð0776/2002/0800Ð0961 $ 06.00
Experimental Section All the reactions were carried out in a domestic microwave oven (Moulinex Microchef, 900 W). N,N-Dimethylhydrazones were prepared from the corresponding carbonyl compounds according to the standard method [15]. All the isolated carbonyl compounds were identified by GLC, IR and NMR and gave satisfactory results in comparison with au-
” 2002 Verlag der Zeitschrift für Naturforschung, Tübingen · www.znaturforsch.com
D
962 Table 1 Regeneration of ketones from N,Ndimethylhydrazones with montmorillonite K-10 under microwave irradiation
Entry Hydrazone 1 R 1 2
1a Ph 1a Ph
CH3 CH3
3
1a Ph
CH3
4 5 6 7 8 9 10 11 12
1a 1a 1b 1c 1d 1e 1f 1g 1h
Conditions
Yield, %a
b
100 50
R⬘
Ph CH3 Ph CH3 Ph CH3CH2 1c 2-naphthyl CH3 PhCH2CH2 CH3 CH3(CH2)5 CH3 CH2(CH2)4CH2 CH2(CH2)5CH2 1-indanone dimethylhydrazone
SiO2 instead of montmorillonite K-10 Al2O3 instead of montmorillonite K-10 in H2O without K-10 in DMF without K-10 b b b b b b b
thentic samples. GC was a Perkin Elmer 8700 with a FID detector under helium as a carrier gas.
trace < 10 < 10 95 89 97 90 88 83 72
a GLC yields and retention times compared with authentic samples; b 1 mmol of substrate, 1 g of montmorillonite K-10, 2 min under microwave irradiation
1 mmol of a N,N-dimethylhydrazone was mixed and ground with 1 g of montmorillonite K-10 in
a mortar. The mixture was transferred to a 20 ml beaker and irradiated in a domestic microwave oven for 2 min. The mixture was irradiated twice, each time for 1 min with 1 min interval. At the end, the mixture was extracted with dichloromethane. Evaporation of the solvent gave the products. Yields were determined by GC.
[1] a) D. E. Bergeiter, M. Momongan, in C. H. Heathcock (ed.): Comprehensive Organic Synthesis, Vol. 2; Pergamon, Oxford (1991); p. 503 and references cited therein; b) D. Enders, L. Wortmann, R. Peters, Acc. Chem. Res. 33, 157 (2000). [2] T. W. Green, P. G. M. Wuts, Protective Groups in Organic Synthesis, 3th ed., Willey, New York (1999). [3] E. Friedrich, W. Lutz, H. Eichenauer, D. Enders, Synthesis 893 (1997). [4] J. S. Panek, R. T. Beresis, J. Org. Chem. 61, 6494 (1996). [5] A. Altamura, R. Curci, J. O. Edwards, J. Org. Chem. 58, 7289 (1993). [6] D. Enders, T. Hundertmark, R. Lanzy, Synlett 721 (1998). [7] M. Avaro, J. Levisalles, H. Rudler, J. Chem. Soc., Chem. Commun. 445 (1969).
[8] R. E. Gawley, E. J. Termine, Synth. Commun. 12, 15 (1982). [9] A. Boruah, B. Baruah, D. Prajapti, J. Sandhu, Synlett 1251 (1997). [10] T. Mino, T. Hirota, N. Fujita, M. Yamashita, Synthesis 12, 2024 (1999). [11] a) E. J. Corey, S. Knapp, Tetrahedron Lett. 3667 (1976); b) T. Mino, S. Fukui, M. Yamashita, J. Org. Chem. 62, 734 (1997). [12] S. Caddick, Tetrahedron 51, 10403 (1995). [13] a R. S. Varma, R. Dahiya, R. K. Saini, Tetrahedron Lett. 38, 8819 (1997); b) S. Chandrasekhar, B. V. Subba Reddy, Synlett 851 (1998). [14] B. K. G. Theng, The Chemistry of Clay-Organic Reactions, Hilger, London (1974). [15] T. Mino, S. Masuda, M. Nishio, M. Yamashita, J. Org. Chem. 62, 2633 (1997).
Typical procedure
Nachdruck Ð auch auszugsweise Ð nur mit schriftlicher Genehmigung des Verlages gestattet Satz und Druck: AZ Druck und Datentechnik GmbH, Kempten
