Fast and Efficient Method for Reduction of Carbonyl Compounds with NaBH 4. Behzad Zeynizadeh* and Tarifeh Behyar

Transcription

1 J. Brz. Chem. Soc., Vol. 16, No. 6A, , Printed in Brzil Sociedde Brsileir de Químic $ Article Fst nd Efficient Method for Reduction of Crbonyl Compounds with NBH 4 /Wet Under Solvent Free Condition Behzd Zeynizdeh* nd Trifeh Behyr Deprtment of Chemistry, Fculty of Sciences, Urmi University, Urmi , Irn As reduções de compostos crbonildos estruturlmente diferentes, como ldeídos, cetons, enis α,β-insturdos e enons, α-dicetons e cyloins form relizds eficientemente com borohidreto de sódio, n presenç de úmido (30% m/m), sem solvente. As reções ocorrerm em tempertur mbiente ou ºC, tendo-se obtido excelentes rendimentos dos produtos correspondentes. A redução quimiosseletiv de ldeídos n presenç de cetons foi obtid com êxito, usndo-se este sistem de redução. Reduction of structurlly different crbonyl compounds such s ldehydes, ketones, α,βunsturted enls nd enones, α-diketones nd cyloins were ccomplished efficiently by sodium borohydride (30% m/m) under solvent free condition. The rections were performed t room temperture or ºC with high to excellent yields of the corresponding products. The chemoselective reduction of ldehydes over ketones ws chieved successfully with this reducing system. Keywords: reduction, NBH 4, wet, solvent free Introduction Reduction is one of the frequently used rections in orgnic synthesis nd vst vriety of reducing gents hve been introduced for this chievement. 1 Among the powerful nd mild reducing gents which hve been developed for the reduction of functionl groups, LiAlH 4 nd NBH 4 re the commonly used regents in synthetic orgnic lbortories. Lithium luminum hydride is n exceedingly powerful reducing gent cpble of reducing prcticlly ll-orgnic functionl groups. Consequently, it is quite difficult to pply this regent for the selective reduction of multifunctionl molecules. On the other hnd, sodium borohydride is reltively mild reducing gent, primrily used for the reduction of rective functionl groups in protic solvents. Consequently the rte of reductions is sometimes slow nd reltively low chemoselectivity is ccompnied with the rections. To control the reducing power of NBH 4, hundreds of substituted boron hydrides hve been reported in chemicl literture nd mny of them re commercilly vilble now. In fct, the progress in this field hs been relized by: (i) substitution of the hydride(s) with other groups which * e-mil: b.zeynizdeh@mil.urmi.c.ir my exert mrked steric nd electronic influences upon the rectivity of the substituted complex ion, 2 (ii) vrition in the lkli metl ction nd metl ction in the complex hydride, 3 (iii) concurrent ction nd hydride exchnge, 4 (iv) use of lignds to lter behvior of the metl hydrides, 5 (v) combintion of borohydrides with metl, metl slts, Lewis cids, mixed solvent systems or some other gents, 6,7 (vi) chnging of the ction to quternry nd phosphonium borohydrides, 8 nd finlly (vii) use of polymers nd solid beds for supporting the hydride species. 9 In this context, we extensively reviewed the pplictions of modified hydroborte gents in orgnic synthesis. 5,10 On the other hnd, the economicl demnds nd the existing stte of environment hve generted need for prdigm shift to perform chemicl rections by using ecologiclly sfe regents or medi. Orgnic rections, crried out in dry medi, hve recently received creful ttention with dvntges ( simply work-up procedure, energy sving, voidnce of solvent wste, dngers nd toxicity) over the solution rections. 11 Literture review shows tht though the reduction of crbonyl compounds s n importnt synthetic methodology ws usully chieved with NBH 4 in protic solvents, this trnsformtion under solvent free condition hs been rrely investigted: e.g., the solid stte reduction

2 Vol. 16, No. 6A, 2005 Fst nd Efficient Method for Reduction of Crbonyl Compounds 1201 of ketones hs been chieved by their mixing with sodium borohydride nd storing the mixture in dry box for five dys. The mjor shortcoming of this method is tht it tkes long time for ny prcticl ppliction. In ddition, the need for lrge mounts of NBH 4 (tenfold) is serious limittion for this method. 12 Reduction of ldehydes nd ketones with NBH 4 impregnted on neutrl Al 2 O 3 under microwve irrdition hs lso been reported. Though the reported method is fst for reduction of ldehydes, in the cse of ketones the need for lrge mounts of NBH 4 (eightfold); nd moderte yields of products re the mjor limittions. 13 In nother report, microwve-ssisted reduction of cetophenone nd ethyl phenyl ketone with NBH 4 in the presence of celite,, Mg nd cellulose under solvent free condition ws investigted, however, the behvior of other ketones ws not further documented. 14 These dys, wet s n inexpensive nd redily vilble regent hs frequently been used in synthetic orgnic lbortories. 15 Therefore, to expnd the bovementioned strtegies nd in our continuous efforts to develop modified hydroborte gents, 5,6 herein, we report mild nd convenient method for fst nd efficient reduction of crbonyl compounds to their corresponding lcohols with NBH 4 /wet under solvent free condition. Results nd Discussion As it ws mentioned, the solid stte reduction of crbonyl compounds cn be chieved by NBH 4 in the presence or bsence of minerl solid supports under norml condition or microwve irrdition with some fcilities nd limittions. However, literture review did not show ny ppliction for such reduction nd the subsequent investigtion of wter influence s wet species on the rte of reductions. Therefore, we decided to study wet ( convenient nd redily vilble regent) s new medi to crry out reduction of crbonyl compounds with NBH 4 under solvent free condition. Scheme 1. Our preliminry experiments showed tht reduction of benzldehyde s model compound with one molr equivlent of NBH 4 in the presence of dry (0.1 g) under solvent free condition took plce with 4-5% conversion fter 3 h t room temperture. However, when this rection ws crried out, prepred by simply mixing smll mount of wter with, the rte of reduction ws drmticlly ccelerted nd the rection ws completed in 1 min, while the lower mount of reducing gent ws required for the complete conversion without using ny solvent, dditives or energy sources (Scheme 1) (Tble 1). These results prompted us to investigte the optimum rection conditions for the influence of wter ccompnied with on this trnsformtion. We exmined set of experiments on the reduction of benzldehyde nd cetophenone s model compounds with NBH 4 under solvent free condition (Tble 1). The results showed tht the reduction of benzldehyde (1 mmol) with 0.5 molr equivlent of NBH 4 in the presence of 10, 20 nd 30% m/m wet (0.1 g ) ws efficient. However, the influence of 30% m/m wet showed fster reduction rte nd therefore it ws selected s the best for the reduction of ldehydes. We then pplied this optiml condition for the reduction of structurlly different liphtic nd romtic ldehydes. The rections were crried out generlly with 0.5 molr equivlent of NBH 4 in the presence of 30% m/m wet in solid stte t room temperture. All rections were completed in less thn 3 min with high to excellent yields of the corresponding primry lcohols (93-99%) (Tble 2). Next, we turned our ttention to the reduction of ketones with the experiment in which cetophenone ws used s Tble 1. Optimiztion of rection conditions nd wet in the reduction of benzldehyde nd cetophenone with NBH 4 under solvent free condition Entry Rection components Molr rtio Medi Condition time (min) Conversion (%) 1 PhCHO/NBH 4 (1:1) Dry RT 3 h PhCHO/NBH 4 (1:0.5) Wet (10% m/m) RT PhCHO/NBH 4 (1:0.5) Wet (20% m/m) RT PhCHO/NBH 4 (1:0.5) Wet (30% m/m) RT PhCHO/NBH 4 (1:0.3) Wet (30% m/m) RT PhCOCH 3 /NBH 4 (1:2) Dry Oil bth 12 h PhCOCH 3 /NBH 4 (1:2) Wet (10% m/m) Oil bth 3 h 70 8 PhCOCH 3 /NBH 4 (1:2) Wet (20% m/m) Oil bth 1.5 h 95 9 PhCOCH 3 /NBH 4 (1:2) Wet (30% m/m) Oil bth PhCOCH 3 /NBH 4 (1:1) Wet (30% m/m) Oil bth 3 h 50 Temperture of oil bth ws C.

3 1202 Zeynizdeh nd Behyr J. Brz. Chem. Soc. Tble 2. Reduction of ldehydes to lcohols with NBH 4 Entry Substrte Product Molr rtio time (s) Yield (%) b mp or bp ( C) NBH 4 / Substrte Found Reported 1 0.5: : : : : : : : : : : : : : : : : : All rections were performed (0.13 g, 30% m/m) under solvent free condition t room temperture. b Yields refer to isolted pure products.

4 Vol. 16, No. 6A, 2005 Fst nd Efficient Method for Reduction of Crbonyl Compounds 1203 model compound. Inherent low rectivity of ketones reltive to ldehydes mde to perform reduction rections in drstic conditions: the reductions were performed with 2 molr equivlents of NBH 4 in the presence of 10, 20 nd 30% m/ m wet t ºC under solvent free condition. Wet (30% m/m) showed fster reduction rte nd the rection ws completed in 42 min (Tble 1). To clrify the influence of wter in wet on this reduction, we crried out solid stte reduction of cetophenone with 2 molr equivlents of NBH 4 in the presence of dry for 12 h t ºC. In this cse, the progress of reduction ws very poor (8-10%) nd the unrected strting mteril ws recovered from the rection mixture. The pplicbility of this reducing system ws further explored with the reduction of structurlly different liphtic nd romtic ketones by using molr equivlents of NBH 4 in the presence of 30% m/m wet under solvent free condition t ºC. These reductions were lso efficient nd the rections were completed within 3-42 min with high to excellent yields of the corresponding secondry lcohols (94-99%) (Tble 3). The work-up procedure of reductions ws esy: wshing the rection mixture with CH 2 nd then drying the solvent over nhydrous N 2 gve the crude product lcohols for further purifiction by short column chromtogrphy on silic gel. The solid stte condition, the esy procedure nd the vilbility of regents prompted us to investigte the pplicbility of this protocol for lrge scle purposes. Therefore, s typicl procedure, we exmined reduction of benzldehyde (5.31 g) with NBH 4 (0.95 g) in the presence of wet (6.5 g, 30% m/m) t room temperture under solid stte condition. We observed tht the rection ws completed in 30 min nd benzyl lcohol ws obtined in 94% yield. This result obviously shows the generl ppliction of this protocol for ny prcticl or industril purposes. The chemoselective reduction of one functionl group without ffecting the other one is well known strtegy for prepring of the molecules with ever-incresing complexity in orgnic synthesis. This subject is of gret interest 16 nd vrious hydroborte gents hve been reported for this chievement. 5,6,17 Since under the defined conditions, reduction of ldehydes nd ketones with sodium borohydride is temperturedependent, therefore, we thought tht this system cn hve chemoselectivity towrds reduction of ldehydes over ketones. This fct ws demonstrted with the selective reduction of benzldehyde over cetophenone using 0.5 molr equivlent of NBH 4 t room temperture under solvent free condition (Scheme 2). The chemoselectivity of the reduction ws perfect nd benzyl lcohol ws obtined s the sole product besides Scheme 2. cetophenone s n intct mteril (Tble 4). The usefulness of this procedure ws further exmined with the reduction of benzldehyde in the presence of benzophenone. We lso observed tht the ldehyde is reduced exclusively. In the next ttempt, we pplied this protocol for the reduction of two ketones such s 9-fluorenone or 4-phenyl-2-butnone versus cetophenone; here, it ws found tht 9-fluorenone nd 4-phenyl-2-butnone were reduced in high chemoselectivity (Tble 4). Regioselective 1,2-reduction of α,β-unsturted ldehydes nd ketones is n esy wy to obtin llylic lcohols which re importnt synthetic mterils in orgnic synthesis. This chievement with NBH 4 is highly solventdependent nd generlly the results do not show useful regioselectivity. 18 Regioselective 1,2-reduction of conjugted crbonyl compounds is usully chieved using modified hydroborte gents, which re formed (i) by the replcement of hydride with stericlly bulky substituents or electron-withdrwing/relesing groups in order to discriminte between the structurl nd electronic environments of the crbonyl groups, (ii) by chnging the metl ction, (iii) by combintion with metl slts nd mixed solvents, nd (iv) finlly immobiliztion on polymeric supports. 5,6,8,18,19 In ddition, the use of non-free hydridic reductnts hs lso been reported for this trnsformtion. 20 The usefulness of this reducing system ws further investigted with the regioselective 1,2-reduction of α,βunsturted crbonyl compounds. We first exmined reduction of cinnmldehyde s model compound with sodium borohydride (30% m/m). The reduction took plce with one molr equivlent of NBH 4 t room temperture under solvent free condition. The rection ws completed in 1 min with perfect regioselectivity. The product cinnmyl lcohol ws obtined in high yield (Tble 5). This procedure ws lso pplied for the reduction of citrl within 4 min t room temperture nd gerniol ws obtined regioselectively in 95% yield. In the next ttempt, we exmined solid stte reduction of conjugted enones with NBH 4 in the presence of wet. Less rectivity of conjugted ketones reltive to ldehydes mde to perform reductions with 2 molr equivlents of NBH 4 t ºC. The results showed tht our procedure ws lso regioselective nd efficient. Regioselective 1,2-reductions of benzlcetone, benzlcetophenone nd β- ionone were chieved successfully with high to excellent yields of the corresponding llylic lcohols (Tble 5). The chemo-

5 1204 Zeynizdeh nd Behyr J. Brz. Chem. Soc. Tble 3. Reduction of ketones to lcohols with NBH 4 Entry Substrte Product Molr rtio time (min) Yield (%) b mp or bp( C) NBH 4 /Subs. Found Reported 1 2: : /745 mmhg 204/ mmhg 3 2: : /1 mmhg 95/1 23 mmhg 5 2: /14 mmhg /14 22 mmhg 6 2: /1 mmhg 80-82/1 22 mmhg 7 2: : : : : : : : /16 mmhg /16 26 mmhg All rections were performed (0.13 g, 30% m/m) in n oil bth t C under solvent free condition. b Yields refer to isolted pure products.

6 Vol. 16, No. 6A, 2005 Fst nd Efficient Method for Reduction of Crbonyl Compounds 1205 Tble 4. Comptetitive reduction of ldehydes nd ketones with NBH 4 Entry Substrte1 Substrte 2 Molr rtio b Condition time (min) Conv.l (%) c Conv.2 (%) c 1 0.5:1:1 RT :1:1 RT :1:1 Oil bth d :1:1 Oil bth d All rections were performed (0.13 g, 30% m/m) under solvent free condition. b Molr rtio s NBH 4 / Substrte 1/ Substrte 2. c Conversions refer to TLC monitoring nd isolted pure products. d Temperture of oil bth ws C. Tble 5. Reduction of α,β-unsturted crbonyl compounds with NBH 4 Entry Substrte Product Molr rtio Condition time Yield mp or bp ( C) NBH 4 /Substrte (min) (%) b Found Reported 1 1:1 RT :1 Oil bth c :1 Oil bth c :1 RT :1 Oil bth c /3 mmhg 107/3 27 mmhg All rections were performed (0.13 g, 30% m/m) under solvent free condition. b Yields refer to isolted pure products. c Temperture of oil bth ws C. nd regioselectivity of this procedure were demonstrted by competitive reduction of cinnmldehyde over benzlcetone (Tble 6 nd Scheme 3). In ddition, selective reduction of cinnmldehyde nd citrl over β-ionone were chieved successfully with this reducing system t room temperture under solid stte condition (Tble 6). Synthetic utilities of vicinl diols re well known nd their preprtions from reduction of α-diketones nd cyloins hve ttrcted gret del of ttention. In this context, we decided to exmine solid stte reduction of α- diketones nd cyloins with NBH 4 in the presence of wet. Reduction of α-diketones to their vicinl diols took plce by 1.5 molr equivlents of NBH 4 in the presence of wet (30% m/m) under solvent free condition t ºC. The product diols were obtined in excellent yields Scheme 3.

7 1206 Zeynizdeh nd Behyr J. Brz. Chem. Soc. Tble 6. Comptetitive reduction of conjugted crbonyl compounds with NBH 4 Entry Substrte 1 Substrte 2 Molr rtio b time (min) Conv.l (%) c Conv.2 (%) c 1 1:1: :1: :1: All rections were performed (0.13 g, 30% m/m) t room temperture under solvent free condition. b Molr rtio s NBH 4 /Substrte 1/Substrte 2. c Conversions refer to TLC monitoring nd isolted pure products. Tble 7. Reduction of cyloins nd α-diketones with NBH 4 Entry Substrte Product Molr rtio time Yield mp or bp ( C) NBH 4 /Substrte (min) (%) b Found Reported 1 1.5: : : : : : : All rections were performed (0.13 g, 30% m/m) in n oil bth t C under solvent free condition. b Yields refer to isolted pure products without ny ssumptions of their simple distereoselectivity (syn or nti). nd ll ttempts to reduce α-diketones into cyloins were unstisfctory by this reducing system (Tble 7). Reduction of cyloins to vicinl diols ws lso chieved successfully by NBH 4 /wet (30% m/m) in solid stte. Using one molr equivlent of NBH 4 t ºC ws the requirement for the excellent yields of the corresponding products (Tble 7). No ssumptions on the simple distereoselectivity (syn or nti) of the products were mde. The influence of wter in wet for the drmtic ccelertion in reduction rections with sodium borohydride is not cler, but we think tht the following fctors my ply role in this ccelertion: (i) The dsorbed wter on the surfce of cn solubilize sodium borohydride nd therefore led to fine dispersion of reducing gent on the surfce of silic gel to do more interction with the substrte; (ii) in the presence of wter with shows Lewis cidity chrcter nd then more interction with the crbonyl group, mke this functionl group susceptible for the hydride ttck; (iii) In our experiments we observed tht wet in the

8 Vol. 16, No. 6A, 2005 Fst nd Efficient Method for Reduction of Crbonyl Compounds 1207 presence of NBH 4 extremely rects with the libertion of hydrogen gs. Therefore, we think tht the generted moleculr hydrogen synergisticlly with the hydride ttck or with the formtion of ctive new species on the surfce of s silic-borohydride ccelertes the rte of reduction; (iv) The borte intermedite which is produced by the rection of borohydride nd the crbonyl group cn be hydrolyzed by the dsorbed wter on the surfce of silic gel nd subsequently shows ccelertion on the rte of reduction. Conclusions In this investigtion, we hve shown tht the presence of smll mounts of wter ccompnied with s wet (30% m/m) drmticlly ccelertes the rte of reduction of structurlly different crbonyl compounds such s ldehydes, ketones, α,β-unsturted enls nd enones, α-diketones nd cyloins with sodium borohydride under solvent free condition. Reduction of ldehydes ws crried out t room temperture nd reduction of ketones t ºC. The chemoselective reduction of ldehydes over ketones ws chieved successfully with this reducing system. Regioselectivity of this system ws lso investigted with exclusive 1,2-reduction of conjugted crbonyl compounds to their corresponding llylic lcohols in high to excellent yields. The usefulness of this protocol ws further shown with the reduction of α-diketones nd cyloins to their vicinl diols in shorter rection times nd excellent yields. Therefore, we think tht in considering high efficiency, chemoselectivity nd perfect regioselectivity which hve been chieved by this reducing system s well s the dvntges of solid stte rections such s simply workup procedure, sving of energy, voidnce of solvent wste, dngers nd toxicity, this procedure cn be ttrctive for syntheticlly useful ddition to the present methodologies. Experimentl All regents nd substrtes were purchsed from commercil sources with the best qulity nd were used without further purifiction. ws used in the form of silic gel 60 ( mesh ASTM) nd ws purchsed from Merck compny. IR nd 1 H NMR spectr were recorded on Thermo Nicolet Nexus 670 FT-IR nd Bruker Avnce DPX- 300 MHz spectrometers, respectively. The products were chrcterized by comprison with uthentic smples (melting or boiling points) nd their 1 H NMR or IR spectr. All yields refer to isolted pure products. TLC ws pplied for the purity determintion of substrtes, products nd rection monitoring over silic gel 60 F 254 luminum sheet. A typicl procedure for reduction of ldehydes with NBH 4 In round-bottomed flsk (5 ml) chrged with (0.1 g), H 2 O (0.03 g) ws poured into nd the mixture ws stirred with mgnetic stirrer to produce wet (0.13 g, 30% m/m). Benzldehyde (0.106 g, 1 mmol) ws then dded to the prepred wet nd the resulted mixture ws stirred for n dditionl 5 min. Afterwrd NBH 4 (0.019 g, 0.5 mmol) s fine powder ws dded to the mixture nd ws stirred for 1 min t room temperture. The progress of rection ws monitored by TLC (eluent; CCl 4 O: 5/2). At the end of rection, the mixture ws wshed three times with CH 2 (3 6 ml) nd the combined wshing solvents were dried over nhydrous N 2. Evportion of the solvent nd short column chromtogrphy of the resulted crude mteril over silic gel (eluent; CCl 4 O: 5/2) gve the pure colorless liquid benzyl lcohol (0.l05 g, 97%, Tble 2). A procedure for lrge scle reduction of benzldehyde with NBH 4 In round-bottomed flsk (50 ml) chrged with (5 g), H 2 O (1.5 g) ws poured into nd the mixture ws stirred with mgnetic stirrer to produce wet (6.5 g, 30% m/m). Benzldehyde (5.31 g, 0.05 mol) ws then dded to the prepred wet nd the resulted mixture ws stirred for n dditionl 5 min. Afterwrd NBH 4 (0.95 g, mol) ws dded to the mixture nd ws stirred for 30 min t room temperture. The progress of rection ws monitored by TLC (eluent; CCl 4 O: 5/2). After completion of the rection, the mixture ws wshed three times with CH 2 (3 25 ml) nd the combined wshing solvents were dried over nhydrous N 2. Evportion of the solvent nd short column chromtogrphy of the resulted crude mteril over silic gel (eluent; CCl 4 O: 5/2) gve the pure colorless liquid benzyl lcohol (5.08 g, 94%). A typicl procedure for reduction of ketones with NBH 4 According to the previous procedure, in roundbottomed flsk (5 ml) chrged with wet (0.13 g, 30% m/m), benzophenone (0.182 g, l mmol) ws dded to wet nd the resulted mixture ws stirred with mgnetic stirrer for n dditionl 5 min. NBH 4 (0.076 g, 2 mmol) s fine powder ws then dded to the mixture nd ws continued to stirring in n oil bth t ºC for 17 min. TLC ws monitored the progress of rection (eluent; CCl 4 / Et 2 O: 5/2). At the end of rection nd cooling to room temperture, the mixture ws wshed three times with

9 1208 Zeynizdeh nd Behyr J. Brz. Chem. Soc. CH 2 (3 6 ml) nd the combined wshing solvents were dried over nhydrous N 2. Evportion of the solvent nd short column chromtogrphy of the resulted crude mteril over silic gel (eluent; CCl 4 O: 5/2) gve the pure white crystlline benzhydrol (0.l82 g, 99%, Tble 3). A typicl procedure for competitive reduction of ldehydes over ketones with NBH 4 In round-bottomed flsk (5 ml) chrged with wet (0.13 g, 30% m/m), benzldehyde (0.106 g, 1 mmol) nd cetophenone (0.12 g, l mmol) were dded to wet nd the resulted mixture ws stirred with mgnetic stirrer for 5 min. NBH 4 (0.019 g, 0.5 mmol) s fine powder ws then dded to the mixture nd ws continued to stirring t room temperture. After 1 min, the mixture ws wshed three times with CH 2 (3 6 ml) nd the combined wshing solvents were dried over nhydrous N 2. Evportion of the solvent nd short column chromtogrphy of the resulted crude mteril over silic gel (eluent; CCl 4 O: 5/2) gve the pure liquid benzyl lcohol s sole product of reduction nd cetophenone s n intct mteril (Tble 4). A typicl procedure for regioselective 1,2-reduction of conjugted crbonyl compounds with NBH 4 in the presence of wet To round-bottomed flsk (5 ml) chrged with wet (0.13 g, 30% m/m), cinnmldehyde (0.132 g, 1 mmol) ws dded to wet nd the resulted mixture ws stirred with mgnetic stirrer for 5 min. NBH 4 (0.037 g, 1 mmol) s fine powder ws then dded to the mixture nd ws stirred for n dditionl 1 min t room temperture. The progress of rection ws monitored by TLC (eluent; CCl 4 / Et 2 O: 5/2). After completion of the rection, the mixture ws wshed three times with CH 2 (3 6 ml) nd the combined wshing solvents were dried over nhydrous N 2. Evportion of the solvent nd short column chromtogrphy of the resulted crude mteril over silic gel (eluent; CCl 4 O: 5/2) gve the pure yellowish liquid cinnmyl lcohol (0.l29 g, 96%, Tble 5). A typicl procedure for reduction of α-diketones nd cyloins with NBH 4 To prepred wet (0.13 g, 30% m/m) in roundbottomed flsk (5 ml), benzil (0.21 g, l mmol) ws dded nd the resulted mixture ws stirred with mgnetic stirrer for 5 min. NBH 4 (0.056 g, 1.5 mmol) s fine powder ws then dded to the mixture nd ws stirred for n dditionl 2 min in n oil bth t ºC. TLC ws monitored the progress of rection (eluent; CCl 4 O: 5/2). After completion of the rection nd cooling to room temperture, the mixture ws wshed three times with CH 2 (3 6 ml) nd the combined wshing solvents were dried over nhydrous N 2. Evportion of the solvent nd short column chromtogrphy of the resulted crude mteril over silic gel (eluent; CCl 4 O: 5/3) gve the pure white crystlline hydrobenzoin (0.21 g, 98%, Tble 7). Acknowledgments The uthors grtefully pprecite the finncil support of this work by the reserch council of Urmi University. The helpful comments of Mr. Mortez Jfri for reviewing the mnuscript re lso cknowledged. References 1. Burke, S. D.; Dnheiser, R. L.; Hndbook of Regents for Orgnic Synthesis, Oxidizing nd Reducing Agents; Wiley- VCH: New York, 1999; Seyden-Penne, J.; Reductions by the Alumino nd Borohydrides in Orgnic Synthesis; 2 nd ed., Wiley- VCH: New York, 1997; Hudlicky, M.; Reductions in Orgnic Chemistry; Ellis Horwood: Chichester, Nryn, C.; Perismy, M.; Tetrhedron Lett. 1985, 26, 1757 nd 6361; Ro, C. H.; Chkrsli, R. T.; Il, H.; Junjpp, H.; Tetrhedron 1990, 46, 2195; Lne, C. F.; Synthesis 1975, Rnu, B. C.; Synlett 1993, 885; Nrsimhn, S.; Blkumr, A.; Aldrichimic Act 1998, 31, 19; Soi, K.; Ookw, A.; J. Org. Chem. 1986, 51, Cinelli, G.; Gicomini, D.; Pnunzio, M.; Mrtelli, G.; Spunt, G.; Tetrhedron 1985, 41, 1385; Blough, B. E.; Crroll, F. I.; Tetrhedron Lett. 1993, 34, Zeynizdeh, B.; Bull. Chem. Soc. Jpn. 2003, 76, 317; Zeynizdeh, B.; Frji, F.; Bull. Koren Chem. Soc. 2003, 24, 453; Zeynizdeh, B.; Zhmtkesh, K.; J. Chin. Chem. Soc. 2004, 51, Zeynizdeh, B.; Behyr, T.; Bull. Chem. Soc. Jpn. 2005, 78, 307; Zeynizdeh, B.; Yhyei, S.; Bull. Koren Chem. Soc. 2003, 24, 1664; Zeynizdeh, B.; Shirini, F.; Bull. Koren Chem. Soc. 2003, 24, 295; Zeynizdeh, B.; Shirini, F.; J. Chem. Res. 2003, Gnem, B.; Osby, J. O.; Chem. Rev. 1986, 86, Firouzbdi, H.; Afshrifr, G. R.; Bull. Chem. Soc. Jpn. 1995, 68, 2595; Firouzbdi, H.; Adibi, M.; Synth. Commun. 1996, 26, 2429; Firouzbdi, H.; Adibi, M.; Phosphorus, Sulfur, Silicon Relt. Elem. 1998, 142, Firouzbdi, H.; Tmmi, B.; Goudrzin, N.; Synth. Commun. 1991, 21, 2275; Yoon, N. M.; Choi, J.; Synlett 1993, 135; Sim, T. B.; Ahn, J. H.; Yoon, N. M.; Synthesis 1996, 324;

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