Synthesis of 1,1-Diacetates from Aldehydes using Trimethylchlorosilane and Sodium Iodide as Catalyst{ Nabajyoti Deka, Ruli Borah, Dipok J. Kalita and Jadab C. Sarma* Regional Research Laboratory, Natural Products Chemistry Group, Organic Chemistry Division, Jorhat, 785006, Assam, India A variety of aldehydes react with acetic anhydride in the presence of trimethylchlorosilane and sodium iodide or trimethylchloro- silane alone to afford1,1-diacetates in excellent yields. Aldehydes may be protected as their 1,1-diacetates by a var- iety of methods. These diacetates are synthetically useful as protecting groups1 having stability towards aqueous acids as well as mild bases,2 and are useful as important building blocks for the synthesis of dienes for Diels�}Alder cyclo- addition reactions.3 Diacetates of some aldehydes are reported to be good cross-linking reagents for cellulose in cotton.4 One European patent claims the peroxygen com- pounds of the type 1,1,5-triacetoxypent-4-ene as activators in the composition of a bleaching mixture for wine stained fabrics.5 Kula has successfully demonstrated in his patent6 the utility of this protecting group in the synthesis of an intermediate for chrysenthemic acid.Recently, several reports have appeared on the synthesis of diacetates from aldehydes using di€erent catalysts.7 Some other methods employed for the preparation of 1,1-diace- tates from aldehydes include the use of protic acids,8 Lewis acids such as BF3,9 PCl3,10 FeCl3,2 etc.and the super acid NaRon-H.11 But in most cases, either a long reaction time (up to 120 h in the case of 2-furaldehyde with PCl3 10), or a low product yield (4% in the case of 4-nitrobenzaldehyde10) is incurred. Herein we wish to report a high yielding method for the preparation of 1,1-diacetates from aldehydes using TMCS�}NaI as catalyst. When an aldehyde was treated with acetic anhydride (1 ml of dry CHCl3 or CH3CN was added to solubilise, if needed) at room temp.[at 0�}5 8C in case of hydroxycitronel- lal (1)] in the presence of a catalytic amount of TMCS (20 mol%) and sodium iodide (20 mol%) it yielded the cor- responding diacetate in excellent yield (Table 1). The same reaction took longer to complete in TMCS alone (reaction in re�Puxing acetonitrile giving a comparable result). A blank reaction of aldehyde, acetic anhydride and sodium iodide failed to react even after 8 h of stirring at room temp.Because of its high yield and short reaction time at ambient temperature this method will better many existing ones.7,11 The catalyst is also easily available, cheap and easy to handle. Experimental Mps were determined on a Buchi capillary apparatus. IR spectra were recorded on a Perkin Elmer 237B IR spectrophotometer. NMR spectra were recorded on a Varian 360L instrument. Mass spectra were recorded on a INCOS 50 GC-MS instrument. General Procedure.DIn a typical reaction a mixture of 2 mmol of benzaldehyde was treated at room temp.with 4 mmol of acetic anhydride followed by 0.4 mmol of TMCS and 0.4 mmol of NaI. J. Chem. Research (S), 1998, 94�}95$ Table 1a Reaction Yield Mp (8C) Entry Substrate time (t/min) (%) found/reported 1 Benzaldehyde 25 87 45^46 (44^452) 2 4-Cl-C6 H4CHO 40 92 79^80 (79^807) 3 4-NO2 -C6H4CHO 40 96 125 (1257) 4 4-MeO-C6 H4CHO 50 96 67^68 (67^6810) 5 Furfural 60 70 55(52^547 ) 6 Butyraldehyde12 40 84 7 Cinnamaldehyde 30 70 85^86 (84^862) 8 Crotonaldehyde12 50 90 9 Gluteraldehydeb 10 Acrolein2 50 60 12 Hydroxycitronellalc 60 70 (2 + 3) aAll the compounds give satisfactory spectral analysis for IR, NMR (60MHz) and MS.Yields are of isolated pure products and mps are uncorrected. bNo reaction in 25% water solution. cThis reaction was carried out at 0^5 8C in 60min. The major products isolatedwere triacetate (2) (50% yield) and diacetate (3) (20% yield) along with a complex mixture ofminor products.$This is a Short Paper as deRned in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there- fore no corresponding material in J. Chem. Research (M). *To receive any correspondence. 94 J. CHEM. RESEARCH (S), 1998When the reaction was over (TLC monitoring) excess water was added and the product extracted with CH2Cl2. The organic layer was washed with a dilute solution of sodium thiosulfate followed by water, dried over anhydrous sodium sulfate and evaporated under reduced pressure.In most cases pure solid products were obtained. We are grateful to the DST, Government of India for ®nancial assistance (grant no. SP/SL/G-34/93) and to their Director for providing the necessary facilities. D.J.K. thanks CSIR, New Delhi for a fellowship. Thanks are also due to Dr N. C. Barua for helpful discussions. Received, 20th May 1997; Accepted, 13th October 1997 Paper E/7/03477F References 1 S. V. Leibermann and R.Connor, Org. Synth. Coll. Vol. III, 1955, 441. 2 K. S. Kochhar, B. S. Bal, R. P. Deshpande, S. N. Rajadhyaksha and H. W. Pinnick, J. Org. Chem., 1983, 48, 1765. 3 B. B. Snider and S. G. Amin, Synth. Commun., 1978, 8, 117. 4 J. G. Frick Jr. and R. J. Harper Jr., J. Appl. Polym. Sci., 1984, 29, 1433. 5 W. R. Sanderson, Eur. Pat. Appl., EP. 125, 781 (1984) (Chem. Abstr. 102, p64010k). 6 J. Kula, Pol. Pat. PL143, 824 (1988) (Chem. Abstr. 112, p216290y). 7 P. Kumar, V. R. Hegde and T. P. Kumar, Tetrahedron Lett. 1995, 36, 601; C. Pereira, B. Gigante, M. J. Marcelo-Curoto, H. Carreyre, G. Perot and M. Guisnet, Synthesis, 1995, 1077; B. P. Bandgar, N. P. Mahajan, D. P. Mulay, J. L. Thote and P. P. Wadgaonkar, J. Chem. Res. (S), 1995, 470. 8 M. J. Gregory, J. Chem. Soc. (B), 1970, 1201. 9 J. March, Advanced Organic Chemistry, Wiley Eastern, New Delhi, 3rd edn., 1986, p. 861. 10 J. K. Michie and J. A. Miller, Synthesis, 1981, 824. 11 G. Olah and A. K. Mehrotra, Synthesis, 1982, 962. 12 N. Deka, D. J. Kalita, R. Borah and J. C. Sarma, J. Org. Chem., 1997, 1563. J. CHEM. RESEARCH (S