Reductive Acetylation of Carbonyl Compounds to Acetates with Pyridine Zinc Borohydride

Transcription

1 76 Bull. Koren Chem. Soc. 2008, Vol. 29, No. 1 Behzd Zeynizdeh et l. Reductive Acetyltion of Crbonyl Compounds to Acettes with Pyridine Zinc Borohydride Behzd Zeynizdeh, * Dvood Setmdideh, nd Frib Frji Deprtment of Chemistry, Fculty of Sciences, Urmi University, Urmi , Irn. * E-mil: bzeynizdeh@gmil.com Received June 26, 2007 Reductive cetyltion of vriety of crbonyl compounds such s ldehydes, ketones nd α,β-unsturted enls/enones ws crried out efficiently with pyridine zinc borohydride, (Py)Zn(BH 4 ) 2, in mixture of THF- EtOAc t room temperture or under reflux condition. The corresponding cettes were obtined in high to excellent yields. In ddition, chemoselective reductive cetyltion of ldehydes over ketones ws chieved perfectly with the regent t room temperture. Key Words : Zinc borohydride, Reductive cetyltion, Crbonyl compounds, Pyridine Introduction Acetyltion of crbonyl compounds is generlly chieved vi reduction followed by the cetyltion. However, the literture review shows tht direct reductive cetyltion of such compounds ws rrely studied. Zn/Ac 2 O/tertiry mines, 1 Zn/Ac 2 O/pyridine, 2 Zn/Ac 2 O/NOAc, 3 CH 3 COCl/ Bu 3 SnH, 4 nd lnthnide complexes/isopropenyl cette 5 re the methods which hve been reported for this trnsformtion. Moreover, the combintion systems of borohydrides hve been lso reported for one-pot reductive cetyltion of crbonyl compounds. The protocol of NBH 4 / EtOAc 6 ws the first report in this subject; however, the method described reductive cetyltion of few crbonyl compounds to their cettes in moderte yields. Moreover, this method ws ccompnied with the reduction, producing crbinols s side products. Tmmi et l. developed the title rection by the ppliction of poly(4-vinylpyridine) supported Zn(BH 4 ) 2 for chemoselective reductive cetyltion of ldehydes over ketones. 7 Though the method is successful in its chemoselectivity, however, long rection times nd moderte yields of products re disdvntges of this method. Recently, we reported pyridine zinc borohydride complex, (Py)Zn(BH 4 ) 2, s bench-top nd verstile reducing gent in orgnic synthesis In the course of our study to discover the new pplictions of this regent, we found tht the reduction of benzldehyde with the regent in ethyl cette provided benzyl lcohol nd benzyl cette. Encourged by the result, we undertook the study for one-pot reductive cetyltion of vriety of crbonyl compounds, such s ldehydes, ketones nd α,β-unsturted enls/enones, to cettes using the regent (Scheme 1). Results nd Discussion We initilly compred the reductive cetyltion rection of benzldehyde in vrious solvents t room temperture (Tble 1). When benzldehyde (1 mmol) ws rected with (Py)Zn(BH 4 ) 2 (1 mmol) in ethyl cette, the rection Scheme 1 Tble 1. Optimiztion of Solvent System in Reductive Acetyltion of PhCHO with (Py)Zn(BH 4) 2 Entry Solvent System (ml) Time (h) Alcohol + Ester (%) 1 EtOAc (3) THF-EtOAc (3:0.3) THF-EtOAc (2:0.2) THF-EtOAc (1:0.1) CH 3CN-EtOAc (3:0.3) The rections were crried out with the molr rtio of PhCHO: (Py)Zn(BH 4) 2 (1:1) t room temperture. provided benzyl lcohol nd benzyl cette in rtio of 40:60, respectively. By chnging solvent systems, the rtio of the formtion of benzyl cette ws drmticlly improved. Among the exmined solvent systems, THF-EtOAc (3:0.3 ml for 1 mmol scle) system provided the best result to give only benzyl cette in 95% yield (entry 2). For other romtic nd liphtic ldehydes, the sme rection ws crried out under the sme conditions. As shown in Tble 2, the rections were completed by 1-3 molr equivlents of the regent within h to give the corresponding cettes s sole products in 79-98% yields. o-phthlldehyde with two ldehyde moieties ws lso successfully converted to the corresponding cette in 92% yield (Tble 2, entry 11). Next, the sme rection ws pplied to ketones. Thus, the rection of cetophenone (1 mmol) ws crried out with lrge excess of the reducing gent (4 mmol) in THF- EtOAc (3:0.3 ml) under refluxing conditions. The rection gve α-phenylethyl cette in 94% yield within 10 h. Similrly, reductive cetyltion of other ketones ws completed by 2-4 molr equivlents of this regent within h under the identicl conditions to give the corresponding cettes s sole products in high to excellent yields (Tble 3). This method lso ws successful for the regioselective

2 Reductive Acetyltion of Crbonyl Compounds to Acettes Bull. Koren Chem. Soc. 2008, Vol. 29, No Tble 2. Reductive Acetyltion of Aldehydes with (Py)Zn(BH 4) 2 Entry Substrte Product Molr Rtio Reg./Subs. 1 1: : : : : : : : : : : : : All rections were crried out with 1 mmol scle of substrte in mixture of THF-EtOAc (3:0.3 ml) t room temperture. b Yields refer to isolted pure products. reductive cetyltion of α,β-unsturted crbonyl compounds (Tble 4). Finlly, bsed on the results in Tbles 2 nd 3, we studied the chemoselective reductive cetyltion of ldehydes in the presence of ketones. We first crried out the competitive reductive cetyltion by recting benzldehyde in the presence of n equimolr mount of cetophenone with one molr equivlent of the reducing gent t room temperture. It ws found tht benzldehyde ws selectively cetylted over cetophenone with perfect selection (Scheme 2). As shown in Tble 5, ll exmined ldehydes were chemoselectively converted over ketones into the corresponding cettes (Tble 5). To show the efficiency of this regent, we compred some of our results with those of chieved by NBH 4 /EtOAc 6 nd poly(4- vinylpyridine) supported Zn(BH 4 ) 2 7 systems. Among those, (Py)Zn(BH 4) 2 provided the best results (Tble 6). The exct mechnism of this synthetic method is uncler so fr. However, we think tht the following mechnistic pthwy plys role in the direct reductive cetyltion of crbonyl compounds with the regent (Scheme 3). In conclusions we hve shown the one-pot reductive cetyltion of vriety of ldehydes nd ketones with (Py)Zn(BH 4 ) 2. Also, the chemoselective reductive cetyltion of ldehydes in the presence of ketones with this reducing gent ws perfectly chieved. In view points of high efficiency, regio- nd chemoselectivity of the rections, mild rection conditions nd the esy work-up procedure, we believe tht this regent cn be considered s suitble nd perfect regent for one-pot reductive cetyltion of vrious kinds of crbonyl compounds. Scheme 2

3 78 Bull. Koren Chem. Soc. 2008, Vol. 29, No. 1 Behzd Zeynizdeh et l. Tble 3. Reductive Acetyltion of Ketones with (Py)Zn(BH 4) 2 Entry Substrte Product Molr Rtio Reg./Subs. 1 4: : : : : : : : : : : : : : All rections were crried out with 1 mmol scle of substrte in mixture of THF-EtOAc (3:0.3 ml) under reflux conditions. b Yields refer to isolted pure products. Scheme 3

4 Reductive Acetyltion of Crbonyl Compounds to Acettes Bull. Koren Chem. Soc. 2008, Vol. 29, No Tble 4. Reductive Acetyltion of α,β-unsturted Crbonyl Compounds with (Py)Zn(BH 4) 2 Entry Substrte Product Condition Molr Rtio Reg./Subs. 1 rt 1: reflux 3: reflux 4: rt 2: reflux 3: All rections were crried out with 1 mmol scle of substrte in mixture of THF-EtOAc (3:0.3 ml). b Yields refer to isolted pure products. Tble 5. Competitive Reductive Acetyltion of Crbonyl Compounds with (Py)Zn(BH 4) 2 Entry Substrte 1 Substrte 2 Molr Rtio b Condition Time (h) Conv. 1 (%) c Conv. 2 (%) c 1 1:1:1 rt :1:1 reflux :1:1 rt < 5 4 1:1:1 rt < 5 5 2:1:1 rt < 4 All rections were crried out with 1 mmol scle of substrte in mixture of THF-EtOAc (3:0.3 ml). b Molr rtio s Reg./Subs. 1/Subs. 2. c Conversions refer to TLC monitoring nd isolted pure products. Tble 6. Comprison of Reductive Acetyltion of Crbonyl Compounds with (Py)Zn(BH 4) 2 nd Other Borohydride Systems Molr Rtio (Reg./Subs.), Time (h) nd Yield (%) Entry Substrte I II 6 III 7 1 (1:1)(2)(95) (1:1)(7)(67) (1:1)(15)(90) 2 (4:1)(10)(94) (1:1)(7)(80) (1:1)(20)(5) 3 (3:1)(1.6)(95) (1:1)(15)(86) 4 (2:1)(0.3)(95) (1:1)(10)(89) 5 (2:1)(0.3)(80) (1:1)(7)(86) (1:1)(20)(8) 6 (1:1)(0.7)(93) (1:1)(20)(80) 7 (2:1)(0.6)(89) (1:1)(18)(80) I (Py)Zn(BH 4) 2; II NBH 4/EtOAc; III Poly(4-vinylpyridine) supported Zn(BH 4) 2

5 80 Bull. Koren Chem. Soc. 2008, Vol. 29, No. 1 Behzd Zeynizdeh et l. Experimentl Section Generl. Pyridine zinc borohydride ws prepred by the reported procedure. 8 All regents nd substrtes were purchsed from Merck nd Fluk compnies with the best qulity nd they were used without further purifiction. IR nd 1 H NMR spectr were recorded on Thermo Nicolet Nexus 670 FT-IR nd 300 MHz Bruker Avnce spectrometers, respectively. The products were chrcterized by their 1 H NMR or IR spectr nd comprison with the reported dte in literture. All yields refer to isolted pure products. TLC over silic gel 60 F 254 luminum sheets ws pplied for the purity determintion of the substrtes, products nd for rection monitoring A Typicl Procedure for Reductive Acetyltion of Benzldehyde to Benzyl Acette with (Py)Zn(BH 4 ) 2. In round-bottomed flsk (10 ml), equipped with mgnetic stirrer, solution of benzldehyde (0.106 g, l mmol) in mixture of THF-EtOAc (3:0.3 ml) ws prepred. (Py)- Zn(BH 4 ) 2 (0.174 g, 1 mmol) ws dded nd the rection mixture ws stirred mgneticlly t room temperture for 2 h. TLC monitored the progress of the rection (eluent; CCl 4 / Et 2 O: 5/2). After completion of the rection, distilled wter (6 ml) ws dded nd the rection mixture ws continued to stirring for 10 min. The mixture ws extrcted with CH 2 Cl 2 (3 7 ml) nd ws then dried over nhydrous sodium sulfte. Evportion of the solvent followed by the preprtive plte chromtogrphy of the resulting crude mteril over silic gel (eluent; CCl 4 /Et 2 O: 5/2) gives the pure liquid benzyl cette in 95% yield (0.142 g, Tble 2). Acknowledgment. The uthors grtefully cknowledge the finncil support of this work by the reserch council of Urmi University. References 1. Gertner, R. J. Org. Chem. 1959, 24, Cvill, G. W. K.; Clezy, P. S.; Whitfield, F. B. Tetrhedron 1961, 12, Aft, H.; Grnt, R. R.; Molyneux, R. J. Tetrhedron 1967, 23, Kpln, L. J. Am. Chem. Soc. 1966, 88, 1833, Nkno, Y.; Skguchi, S.; Ishii, Y. Tetrhedron Lett. 2000, 41, Ro, B. R.; Nmbudiry, M. E. N. Synth. Commun. 1991, 21, Tmmi, B.; Goudrzin, N.; Kist, A. R. Eur. Polym. J. 1997, 33, Zeynizdeh, B.; Frji, F. Bull. Koren Chem. Soc. 2003, 24, Zeynizdeh, B.; Zhmtkesh, K. J. Chin. Chem. Soc. 2003, 50, Zeynizdeh, B.; Zhmtkesh, K. J. Chin. Chem. Soc. 2004, 51, Zeynizdeh, B.; Zhmtkesh, K. J. Chem. Res. 2003, Zeynizdeh, B.; Zhmtkesh, K. J. Chin. Chem. Soc. 2005, 52, Pouchert, C. J.; Behnke, J. The Aldrich Librry of 13 C nd 1 H FT- NMR Spectr; Aldrich Chemicl Co.: Milwukee, Mhmmdpoor-Bltork, I.; Aliyn, H.; Khosropour, A. R. Tetrhedron 2001, 57, McKillop, A.; Ford, M. E. Tetrhedron 1974, 30, Hilborn, J. W.; McKnight, E.; Pincock, J. A.; Wedge, P. J. J. Am. Chem. Soc. 1994, 116, () Joshi, D. K.; Gold, M. H. Eur. J. Biochem. 1996, 237, 45. (b) Pincock, J. A.; Wedge, P. J. J. Org. Chem. 1994, 59, Picrux, L. B.; Smeigh, A. L.; Guo, D.; McCusker, J. K. Inorg. Chem. 2005, 44, Bhushn, V.; Chkrborty, T. K.; Chndrsekrn, S. J. Org. Chem. 1984, 49, Zrbin, P. H. G.; Reckziegel, A.; Plss, E.; Oliveir, A. R. M.; Simonelli, F.; Mrques, F. A. J. Brz. Chem. Soc. 2000, 11, Ishihr, K.; Kubot, M.; Kurihr, H.; Ymmoto, H. J. Org. Chem. 1996, 61, Nik, S.; Kvl, V.; Gopinth, R.; Ptel, B. K. Arkivoc 2006, (i), Nik, S.; Kvl, V.; Gopinth, R.; Ptel, B. K. Arkivoc 2006, (xi), Buckinghm, J.; McDonld, F. Dictionry of Orgnic Compounds, 6th ed.; Chpmn & Hll: New York, Khn, A. T.; Islm, S.; Mjee, A.; Chttopdhyy, T.; Ghosh, S. J. Mol. Ct. A 2005, 239, Bosco, J. W. J.; Siki, A. K. J. Chem. Soc. Chem. Commun. 2004, Humber, L. G. J. Med. Chem. 1965, 8, Orit, A.; Tnhshi, C.; Kkud, A.; Oter, J. Angew. Chem. Int. Ed. 2000, 39, Ternishi, R.; Flth, R. A.; Gudgni, D. G.; Lundin, R. E.; Mon, T. R.; Stevens, K. L. J. Agr. Food Chem. 1966, 14, Procopiou, P. A.; Bugh, S. P. D.; Flck, S. S.; Inglis, G. G. A. J. Org. Chem. 1998, 63, Chen, C.-T.; Kuo, J.-H.; Pwr, V. D.; Munot, Y. S.; Weng, S.-S.; Ku, C.-H.; Liu, C.-Y. J. Org. Chem. 2005, 70, Choi, J. H.; Choi, Y. K.; Kim, Y. H.; Prk, E. S.; Kim, E. J.; Kim, M.-J.; Prk, J. J. Org. Chem. 2004, 69, Byers, J. J. Org. Chem. 1983, 48, 1515.