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ao4omom Tetmhedron Vol. 48, No. 22, PP.46234628.1992 Printed in Gnat Britain Convenient Methods for the Reduction of Amides, Nitriles, Esters, Acids and Hydroboration AS. smo+.oo Pcrgamm Press Lad Bhanu Prasad, J.V. School of Chemistry, Carboxylic of Alkenes Using NaBH&System Bhaskar University Kanth and Mariappan of Hyderabad, Periasamy* Hyderabad 500 134, India (Received in UK 8 April 1992) system in THF gives the corresponding Abstract: Reaction of amides with NaBli4-12 amines in 70-76% yields. Reduction of nitriles yields the corresponding amines in 70-75% yields. The I /NaBH4 system is useful in the hydrobor_ation of olefins and the corresponding alcohols The reagent system is also useful are o 6 tained in 78-92% yields after H202/?H oxidation. for the reduction of carboxylic esters and acids to the corresponding alcohols in 60-9096 yields. The NaUH4 does The efforts to increase discovery of hydroboration conditions. lead to whicti the efforts of functional reported are groups that and arnines It reduces has been of Al though, much I2 with attention the in mixture We wish that (10 mmol) the corresponding to those R2SeBr2.3 and It NaB03 BH3:SMe2,7 reported observed that by olefin (15 mmol); regio BH3:THF,’ addition here pure reduction corresponding under condi- C2H5) shown convenient and acids alcohols reflux or has been for diborane accessible mmol) 2.511 at 1-4 can reagent that and that the procedures into for alcohols of amine of carboxylic and followed in Table NaBH /ZnC12/N,N-diethylaniline 4 hydroboration of olefins with the receive system is useful boranes.5 Addition of an arnide by refluxing I). by did not acid group to alcohol.6 into a mixture O’C be oh taincd system the 12/NaBH4 preparation reduction (entries of I2 (2.8 stirring The 2 yields in are THF 12/NaBH4 observed mmol) to NaBH4 (7 for 2h at room temperature gives the corresponding and stereoselectivities BH3:SMe29 the (or) imide for 3h gives comparable and in THF NaBH4/ followed give alcohols.’ followed or H202/NaOAc that that in the of 12 (IO yield for = CH2CH2Br It diborane and BH3:NR3). it has been recently amine esters We have reported in TIHF 70-7696 describe readily leads to selective mmol) in using has been with (23 amine (R of acids system. utilization the addition We have NaOH The NaUH4 reported by oxidation O°C here for the amines. carboxylic tilnc this applications. of diborane of I2 to RCOOH/NaBH4 to report a long to R2SeBr2 We amines, in diglyme, in synthetic generation for of borane. to methods arnbient Lewis generation For example, reduced under using BH3:SMe2 of a tertiary corresponding using the NaBH4/12 known NaBH4 a mixture for convenient are acids esters BH3:THF, additives. amides the gives nitriles other and towards methods (e.g. in the presence to THF and has been and that nitriles and forms developing with esters NaBH4 olefins’ for along reported of alkenes il of esters carboxylic of in various in THF and amides also hydroboration of also nitriles, reactivity continuing acid system reduction reaction still amides R2SeBr2/NaBH4 the using NaBH4 carboxylic NaBH4 amides, available using NaBH4/ZnC12 tions.2 for reduce is now commercially However, the not alcohols here and BH :N,N-diethylaniline 3 are 5 4623 in 78-92% similar complexes to mmol) in THF and oxidation yields (entries those for reported (25 with ml) 1-5 in Table previously the hydroboration a; H202/ 2). using of alkenes. A. S. BHANU PRASAD et 4624 Table I: Reduction S.No. of amides and nitriles using 12/NaBH,,.a Ph Ph 3 70°C 1. (%) Ph .I‘ 76 (6h)b =o o= b Yield Productd Conditions Temp. (Time) Substrate Ph al. h N &ti2Ph &Ph 2. PhNCH3COCH3 70°C(3h)C PhNCH3C2H5 74 3. PhNHCOCH3 70°C (3h)’ PhNHC2H5 75 4. PhCONH2 70°C (3h)’ PhCH2NH2 70 70°C (3h)= 5. CH&N 74 CHpCHINHl 6. PhCH2CN 70°C (3h)’ PhCH2CH2NH2 72 7. PhCN 70°C (3h)’ PhCH2NH2 70 70°C (3h)’ CH3(CH2)7CH2NH2 75 8. a) The experiments and adding 12 in THF and imide were (5 mmof) used. (d) Selective an ester 5, Table (20 were ml) out by taking the in portions for 2.5h used. (c) NaBHQ (23 mmol), products hydroboration group However, the mixture We have 0°C The carried were of as illustrated identified olefinic by the at 0°C. can be and NaBHo (b) NaBl-l@ (27 I2 (IO spectral by group substrates mmol) data hydroboration-oxidation fH when of mrnof), NMR it (25 l2 (12 and amide/nitrife (In, achieved in THP and is present mi) mmof) (10 mmol) 13C NMR). along methvl-IO-undecenoate with (entry 2). the addition at were for in 94% yield, carboxylic esters of I2 (5 mmol) for 0.5h after also observed 2.5h followed indicating 2NaBH4 can the addition that by the THF reduced to (12 mmol) addition of corresponding esters I2 (5 mmol) of Ph3P of BH3:THF + 2NaI the in THF of carboxylic addition the formation + I2 be and NaBH4 + Ii2 (10 NaBH,, mmol) in the reaction I PPh3 PPh3:BH3 for in 86-g!?% by 2.5h and refluxing 1 and 3, Table 3). (entries to + 2BH3:THF alcohols (30 ml) at 0°C (I2 in THF mmol) (20 of NaBH4 in THF ml) gives with 12. (30 ml) Ph3P:BH3 Reduction using NaBH& Table 2: Hydroboration of alkenes using 12/NaBH4 in THF.a Yield Producte Conditions Temp. (Time) Substrate S.No. 4625 system (%) 1. PhCH=CH2 25°C (2h)b PhCH2CH20Hf 90 2. CgH,2CH=CH2 25°C (2h)b CgH, 2CH2CH20H 92 OH 0 3. \ 4. 25°C (4h)’ 85 25°C (4h)’ 81 6 5. (a) The the 25°C experiments addition mmols) mmo]) of were were carried used and and the the (15 mmoi) The products were identified with data reported parison \vaS 20% (‘H NMR In all known order the avoid 0.5h at O’C without We have lcads to When the purified organoboranes the by were were the data (IR, mmol), chromatography. was NMR (f) Contains the reduction (I and/or also react l2 in THF possible cleavage significant reported of of that THF. H202/OH-. H202/OH-. followed by (b) Alkenes (15 (c) Alkenes (10 (d) Olefinic ester oxidized using H202/NaOAc. and NMR) and also by com- the 13C isomeric (e) l-phenylethanol upto However, carboxylic acid the this problem addition of can iodine by the to give slowly However, successive acids.6 from required B-1 in portions the addition stoichiometry, species which to NaBH4 time since can are in THF it is known at be reduced 0°C to in results. carboxylic II) derived with was added of change than addition 1 his method was attempted THF cleavage I were of RCOOH gives in >50 good mmol and I2 into results scale in NaBH4 10 in THF mrnol substantial scale. amounts also obtained. -/-7_OCOR I by ‘H I2 (2.8 using using species literature. IfiOH lowed column oxidised oxidised organoborane by spectral in complexes recently reduction of products were organoboranes and NaBH,, (7 mmol), taking by , we have used NaBHo more ‘BH3’ ethers.“Also, to (2h)d analysis). cases that to cleave in utilized out Products alkenes. utilized were “O-f-GcoocH3 78 CooCH3 -4 II be circumvented carboxylic acid. The by the addition corresponding of I2 into alcohols are NaBH4 at 0°C obtained in folgood A. S. BHANUPRASADet al. 4626 yields after in the the work reduction reduction acid into of boration of (entries of olefinic of 3 and acids IO-undecenoic NaBH4 addition canoic up in THF 12 into the double acid (20%) at NaBH4 Table 3). However, is lost by performing acid room gives followed followed of the in this way. yield by addition after by acid (59%) oxidation the with For example, 0°C6 leads and observed addition of I2 at of carboxylic l,ll-undecanediol 31 are obtained chemoselectivity reaction in 89% by addition a mixture 5 in Table the IO-undecenol temperature at 0°C bond and (entry 4, of the However, to the hydro- II-hydroxy. H202/OH- unde- and protono- lysis. In conclusion, of amides, Table 3: the nitriles, Reduction S.No. readily accessible carboxylic esters of carboxylic esters Substrate reagent 12/NaBH4 system is useful and acids and also for hydroboration and acids using 12/NaBH4 in the reduction of alkenes. in THF.a Conditions Temp. (Time) Yield 1. PhCH2COOEt 70°C (0.5hJb PhCH2CH20H 85 2. CH3(CH2&COOCH3 70°C (0.5hIb CH3(CH2)8CH20H 89 3. CH3(CH2&COOH 25“C (lh)’ CH3(CH218CH20H 90 Br r+ 4. (%) Br coon cH#H 25°C (lh)’ 8 ti Br Br 5. 25°C 86 8 Ho-fK CHzoH (IhI’ 59 20 (a) Experiments (12 mmol) fluxed were for at were 0°C 0.5h. isolated carried for (cl out 2.5h. The (b) After acids were by chromatography fied by spectral data (IR, by adding H ‘ the addition added at on silica NMR, I2 (5 mmol) gel General: Tetrahydrofuran Infrared polystyrene deuterated are as reference. chloroform expressed distilled spectra in ppm using freshly were NMR column the ml) the reaction mixture reagent. (dl The products 12/NaBH4 in portions (hexane/ethylacetate eluent) to NaBH4 was re- and identi- benzophenone-sodium on a Perkin-Elmer were recorded silane as internal spectra from SECTION over recorded tetramethyl downfield the ester, to (30 13C NMR). EXPERIMENTAL experiments. of 25“C in THF the signal for on a JEOL-FX-100 standard. internal was used for 1R spectrometer Me4Si. The For all 1310 spectrometer chemical TLC shifts plates the with in ( 5) coated 4627 Reduction using NaBH& system with silica gel chamber. were For run column in hexane/ethyl acetate chromatographic mixture purification and under spots were gravity, column developed grade in iodine silica gel (IOO- 200 mesh size) was employed. Reduction (I g, 27 g, I2 mmol) mmol) mixture 3N ml). The in dry in dry was with (5 was evaporated liberate matography on silica 3025, 2900, gel 7.16-7.68(m, 1600, 15H). 13C the and aqueous amine borane The layer 730, I, I) 6: 129.8, NaOH MgSO4. F3B.0Et2 129.0, (8 (3 x IO ml). followed was purified 1.2g The destroyed anhydrous by chro- (76%). 3.08-3.6 I2 (3 2.5h. 3N ether with Table Yield: 139.8, using over was treated for carefully with and dried NMR(CDC13) : 144.9, MHz) NMR(25 brine (entry ‘H was of NaBH4 flask. 0°C neutralized acetate/85:15). 690. at hydride was residue product round-bottom was extracted water, (hexane:ethyl 1450, it to a slurry atmosphere excess ceased, with capped nitrogen and washed amine. column 2850, 0°C (15 ml) was added septem under evolution and the free a two-neck to gas were the in dry THF added cooled the extracts to 2H), 6h; in was was separated organic solvent ml) ml) After layer g, 5 mmol) (15 (20 for by aq.NaOH 3050, THF ml). organic (1.7 THF refluxed HCI The combined The lmide of imide: (m, 128.0, IR(cm-‘1: 6H), 3.96(s, 127.6, 126.1, 63.1, 60.8, 53.8. Reduction were 8, in dry IO mmol) 2.5h. The troyed lized THF in dry ted ether over 2800, 2H), 1600, (2 Na13H4 THF (30 for (8 ml) was to 0°C and was brine gel 750, MHz) and 660. 3N HCI solvent gel 690. slowly 3 g of with dried NaOH ether over organic and 136.7, 128.5, In a the was contents added. The (3 x 10 ml). 1.9 126.5, THF The MgS04. (s, 41.5, 34.2, was layer was I.1 2.6(m, 20.9. was 0.5h. and 2NH), 2950, 11.0. flask, taken nitrogen in dry atmosphere to O”C, 6N HCI mixture and and 6.54-6.7(m, the was cooled aqueous was washed with chromatographed IR(crr~-~): 5.3(bs, 3020, were The extract brine round-bottom under separated organic concentrated 4H), capped neutra- by column 2H), 37.2, for des- was extrac- lR(cm-‘1: 46.6, 0°C was water, 3h. It was cooled for g (74%). it 3.38(q, 10 mmol) added for organic combined 3H), septem refluxed It 6H), ml) at (2.54 hydride was purified (74%). 112.4, (1.45g, were Yield: Ig 2.84(s, 116.0, (70°C) Iodine layer with product Yield: (20 ceased, and the aqueous 3H), g, 23 mmol) flask. atmosphere was washed two-neck (0.88 to O”C, the excess and the 129.1, was refluxed nitrogen gas evolution extract 1.12 (t, : 149.1, in dry mixture anhydrous NMR(CDC13)6: the was removed MHz) (hexane:ethylacetate/60:40). ‘H under 3,5-dimethylbenzylcyanide mmol) The reaction added After and NaBH4 round-bottom 3h; cooled was separated NMR(CDC13)6: and g,lO capped (hexane:ethylacetate/95:5). ‘H 13C NMR(25 mmol) for ml). combined IO mmol) in portions layer The I2 (2.54 2.5h. : 138.4, (6 The organic g, septem (70°C) The 740, 23 extracted column of (1.49 added 3,5-dimethylbenzylcyanide: g, ml). at 0°C was ml). 2H). of (0.88 ml) MgS04. on silica 7.08-7.24(m, amide in a two-neck was refluxed (8 ml). x I5 1450, Reduction (20 addition anhydrous chromatography ml) mixture by careful with (25 THF reaction using 3N NaOH dried The of N-methylacetanilide: taken 3400, 2950, 6.5(s, 3H). layer water, on silica 2800, 13C 1600, NMR(25 A. S. BHANUFQASADet al. 4628 Hydroboration 7 mmol) under of nitrogen tion mixture added and atmosphere washed purification of 2.44(bs, of in I2 (6.4 through To this in THF The The with 3N NaOH MHz) Acknowledgement: to UGC : 62.1, We are for Special 1050. to extent slowly the solution, 36.1, 35.7, grateful to Assistance 32.2, CSIR, New and COSIST signals of 2.5h Ih at ether 20% 1. Brown, Yamakawa, H.C; 3. Akabori, .4. Freeguard, 5. Narayana, 6. Bhaskar 7. Brown, 8. Kabalka, 9. Brown, Subba Rao, B.C. T; Masaki, S; Takanohashi. G.F; H.C; J.V; Choi, G.W; H.C; 10. Narayana, Long, L.H. Chem. C; Kabalka, & Ind. 25°C. over 28.5, 26.4, Delhi for (30 DiLHCI MgS04. 3325, P.P; Narayana, Synthesis 1956, 78, 5694. Sot. Jpn. 1991, ml) (20 2850, support. 64, 2730. 482. Chem. 1987, 323, Chem. 1991, 56, 5964. C. J. Chem. via Boranes, G.W; Tetrahedron Trans.1 1991, Wiley Lett. 1982, 1990, 145. 47, 3153. Ed., 1990, Interscience, 31, 6977. observed. (2.1 the g, slurry equalizer was ml, Evaporation financial Sot. Chem. also added 3N) The combined 2900, 3H), and 4.72 was organic of solvent 1450, 1050. 25.4. Chem. S; J. Org. 1.44(d, I.44 a pressure Programmes. Perkin 1.68 g To 1965, 471. M. J. Org. Narasimhan. Wadgaonkar, Organic Sot., M. J. Organomet. Periasamy, Y.M; Chem. H. Bull. Y. J. Chem. C; Periasamy. Kanth, J. Am. M; Nohira, solvent NaBH4 REFERENCES 2. extract of at flask. in THF was was separated are through (3 x 20 ml). IR(cm-‘): 29.1, ml) organic NMR(CDC13)6: The 50 mmol) and dried g (90%). (20 evaporation round-bottom for with brine 15 g, stirred was extracted layer scale) using NaBH4/12: during (17.2 further ‘H 5H). g, and the reac- THF combined On (0.27 (hexane:ethylacetate/90:10), two-necked acid Yield: 52.8, in was added were layer IO,ll-dibromoundecanol. 13C NMR(25 taken The 7.0-7.32(m, acid (50 mmol was contents 1600, IH), (2 ml), The organic MgSO4. NaBH4 (15 ml) was added was added water 10 ml). column I-phenylethanol (60 ml) aqueous gel 3300, 4.72(q, with 30 ml). x flask in dry THF g, 15 mmol) anhydrous silica IR(cm-l): ml) (3 over on 2H), (1.5 (3N, ether dried presence (120 Styrene round-bottom g, 2.8 mmol) It was quenched IO,ll-dibromoundecanoic was washed thankful the THF added. afforded 3.7(t, 0°C. with IO,ll-dibromoundecanoic dry a cannula. carefully layer to g, 25 mmol) 0°C. and isolated. 2H), capped (0.71 30 ml)/NaOH extracted brine were corresponding mmol) at spetem Iodine 25°C. chromatography 2.78(t, 60 2.5h 2h at was water, by alcohols Reduction at layer with IH), for using H202(30%, aqueous was (25 ml). over was stirred and (90%) In a two-neck in dry THF and oxidized the ppm styrene: was taken 67, 975. New York, 1975. We are also