Kad, G L

Kaur, Kanwal Preet

Singh, Jasvinder

Singh, Vasundhara

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Indian Journal of ChemistryVol. 378, February 1998, pp. 172 - 173Microwave assisted preparation of1,3-dithiolanes under solvent freeconditionsG L Kad·, Vasundhara Singh, Kanwal Preet Kaur &Jasvinder SinghDepartment of Chemistry, Panjab University,Chandigarh 1600 14, IndiaReceived 16 October 1997; accepted 22 January 1998Various carbonyl compounds react efficiently with 1,2-ethylenedithiol by microwave irradiation using mildlyacidic K-I0 clay within a few minutes and furnish theproducts in high yield under solvent free conditions.NoteProtection and deprotection of functional groupsIare important steps in multiple step synthesis ofnatural products. For such conversions the hunt forsimpler, time saving and environment friendlymethods is continuously on by organic chemists.To augment this search use of domestic microwaveoven in conjunction with solid support in dryconditions is well documented in literature'.1,3-dithiolanes are widely employed forprotection of carbonyl compounds as they are inertupon attack by nucleophiles and reducing agents.Anhydrous iron (III) chloride' dispersed in silicagel and sulphonated charcoal" under heterogeneousconditions are used as catalyst and are reported byTable I-Preparation of 1,3-dithiolanesEntry Reactant Rxn time Product Yield (%)(tlmin)\.Cs~>=O7 90C6HsXS]H H's2.C6HS)= 7 80CsHs SJ-0 XCH3 CHI S3.C6HS) 0 7 75CsHs SJX/C6HS CsH5 S4. 0 7 80II n<:=©rC'H ~~5. 0 7 n 80"MC'H ifSo 'HH3CO ~co/6. 0 7 n 70©6 007. OH 0 7 75.2&' OHfio C"H if~(a)All the products were characterised by spectral (lR, NMR) and elemental analysis(b )Purity of compound was determined by TLC analysisPatney for this conversion. Recently some othercatalysts such as H-Y zeolite', anhydrouslanthanum trichloride" and acidic ion exchangeresin 7 have been used for the thioacetalisation ofcarbonyl groups, but all these have one or the otherdrawbacks such as long reaction time, loweryields, use of highly carcinogenic solvents,expensive reagents and high temperature. Incontinuation of our work" we herein report a veryclean, time saving and high yielding method forpreparation of 1,3 dithiolanes from variousaldehydes and ketones.o H~H~ .R.... 'R' K-10 Clay, MW, 640 W7 min.This is a simple procedure for protection ofcarbonyl groups under very mild conditions withthe advantages of (i) high yield, (ii)manifoldreduction in reaction time, and (iii) solvent freeconditions shall find large application in naturalproduct synthesis.Experimental SectionIH NMR spectra were recorded in CDCl3 orCCl4 on a Varian EM-360 (90 MHz) spectrometerusing TMS as internal reference (chemical shifts in8, ppm) and IR spectra as liquid films on a Perkin-Elmer infrared model 1430 spectrophotometer(vmaxin cm'). Unless otherwise stated all organicextracts were dried over anhyd. Na2S04• Purity ofall analytical samples was checked by TLC.Microwave reactions were carried out in BPLDMO 700T (640 W) microwave oven.NOTES 173General procedure. In a 250 mL beakeractivated K-I0 montmorillonite clay (O.l2g) wastaken and a mixture of carbonyl compound(Immole) and 1,2-ethylene-dithiol (1.5mmole) wasadded. The beaker was covered with a watch glassand exposed to microwave irradiation at 640W for7 min. The product was extracted with diethylether (3xlOmL), washed with brine and dried.Evaporation of solvent under reduced pressuregave the desired products in (75-80%) yield asreported in Tablel.AcknowledgementThe authors are thankful to the CSIR & UGC,New Delhi for providing financial support for thiswork.References1 Greene T W, Protective groups in organic synthesis,(Wiley, New York), 1981.2 a) Latouche R, Texier-Boul1et F & Hamelin J,Tetrahedron Leu, 32, 1991, 1179; b) Bram G, Loupy A,Majdoub M, Guttemiez E & Ruiz-Hitzky E, Tetrahedron46, 1990, 5167; c) Rechsteiner B, Texier-Boulled F&Hamelin J, Tetrahedron Lett, 34,1993, S071; d) TouauxB, Klein B, Boullet F & Hamelin J, J Chem Res (S), 1994,l\6.3 Patney H K, Tetrahedron Left, 32,1991,2259.4 Patney H K, Tetrahedron Left, 32,1991,4\3.5 Kumar P, Reddy R S, Singh A P & Pandey B,Tetrahedron Left, 32,1991,825.6 Garlaschelli L & Vidari G, Tetrahedron Left, 31, 1990,5815.7 Maiti A K, Basu K & Bhattacharya P, J Chem Res (S),1995, 108.8 a) Singh Vasundhara, Kaur Kanwal Preet, Singh Jasvinder& Kad G L, J Chem Res (S), 1997, 58; b) Kad G L, SinghVasundhara, Kaur Kanwal Preet & Singh Jasvinder,Tetrahedron Left, 1997, 1079.

Microwave assisted preparation of 1,3-dithiolanes under solvent free conditions

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Microwave assisted preparation of 1,3-dithiolanes under solvent free conditions

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