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Reaction of Thexylbromoborane-Methyl Sulfide in Methylene Chloride with Selected Organic Compounds Containing Representative Functional Groups T

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Reaction of Thexylbromoborane-Methyl Sulfide in Methylene Chloride with Selected Organic Compounds Containing Representative Functional Groups T Reaction of ThxBHBr- SMe2 with Organic Compounds Bull. Korean Chem. Soc., Vol. & No. 4, 1987 313 stirred solution of 2.5 equivalents of LDA in 30mL of dry HRMS: Calcd for C16H17NO2: 255,1259, Observed: THF was added 0.33 g(0.0014 mole) of 10 in 5 mL of dry 255.1254. THF at -78°C under nitrogen. After 10 min, 0.22 mL(1.5 eq.) of 1 f3-dibromopropane was added to the reaction mix­ Acknowledgements. The partial support of the Montana ture and stirred overnight at rt. Work-up as usual gave 0.093 Agricultural Experiment Station is gratefully acknowledged. g of liquid(24% yield). One of the authors(J.-G. Jun) wishes to dedicate this work to NMR:$7.27(5H,br s); 4.60(2H,s); 2.06(4H,m); Professor Nung Min Yoon on the occasion of his 60th birth­ L70(4H,m); 1.50(4H,m). day. 13C NMR：ai81.7(s),136.3(s),128.6(d),128.2(d),127.7(d), 63.4(s),42.4(t),36.4(t),27.4(t). References MS: 269(M + , base),241,229,213,200,185,172,145,132, 109,91,79,66. 1. (a) D. Wilkening and B. P. Mundy, Synth. Commun., 14, HRMS: Calcd for C17H19NO2: 269.1413. Observed: 227 (1984); (b) C. Girard and R. Bloch, Tetrahedron 269.1403. Lett., 3683 (1982); (c) K. G. Bilyard and P. J. Garrett IR: 2941,1709(C = O),1399,1353,1147,969,701. Tetrahedron Lett., 1775 (1981). 2. D. Wilkening and B. P. Mundy, Synth. Commun., 13, 3-(N-Benzyl)-2,4-dioxotricyck)(3.3.2J)m(mane,12. 959 (1983). 1.2- Dibromoethane(0.9 mL, 1.5 eq.) was used instead of 3. (a) S. W. Baldwin and R. E. Gawley, Tetrahedron Lett., 1.3- dibromopropane as the synthesis of 11 (25% yield). 3969 (1975); (b) P. Narasimha Rao, J. Org. Chem., 36, 】H NMR: ^7.6-7.25(5H,m); 4.63(2H,s); 2.32-1.53 2426 (1971); (c) See the following communication for our (10H,m). synthesis of valerane. MS: 255(M + ,base),227,199,171,150,136,123,108, 4. Leo A. Paquette, J. Am. Chem. Soc., 93, 4508 (1971). 91,79,65. 5. H. Kasugai, Japan Kokai 75, 121, 433 (1975). Reaction of Thexylbromoborane-Methyl Sulfide in Methylene Chloride with Selected Organic Compounds Containing Representative Functional Groups t Jin Soon Cha*, Jin Euog Kim, and Se Yeon Oh Department of Chemistry, Yeungnam University, Gyongsan 632. Received April 20,1987 The approximate rate and stoichiometry of the reaction oi excess thexyioromoborane-methyl sulfide, ThxBHBr-SMe2, with 0°C) were studied in order to characterize the reducing characteristics of the reagent for selective reductions. The selectivity of 사 )e reagent was also compared to the selectivity of thexylchloroborane-methyl sulfide. Thexylbromoborane appears to be a much m가 der and hence more selective reducing agent than thexylchloroborane. The reagent 은 rates many organic func­ tionalities. Thus, the reagent shows very little reactivity or no reactivity toward 휺 cid chloride옹 ， esters, epoxides, amides, nitro compounds including simple olefins. However, this reagent can reduce aldehydes, ketones, carboxylic acids, nitriles, and sulfoxides. Especially the reagent reduces carboxylic acids including cr ,^-unsaturated ones and nitriles to the correspon­ ding aldehydes. In addition to that, thexylbromoboran은 shows good stereoselectivity toward cyclic ketones, much better than the chloro-derivative. Thexylchloroborane-methyl sulfide has appeared to be a plored the reducing characteristics of the reagent systema­ fascinating reducing agent for the selective reduction of or­ tically. ganic functionalities1, especially for the direct reduction of Thexybromoborane-methyl sulfide can b은 prepared r■은 adi- carboxylic acids to the corresponding aldehydes2. It is believ­ ly from the addition of 2,3-dimethyl-2-butene (tetramethy­ ed that this unique reducing characteristics is due to the lethylene) to monobromoborane-methyl sulfide in methylene introduction of chlorine atom to thexylborane3, which pro­ chloride (eq.l). vides such fascinating selectivity and specificity. This in­ trigued us. Consequently, we prepared thexylbromoborane- >=< + BH2Br-SMe2 으 坚竺耳安月 SMe2 (1) methyl sulfide, which is analogous to the chloro-derivative in / 1 structure but different in electronic and steric effect, and ex- t Dicated to Professor Nung Min Yoon on the occasion of his 60th The reagent, ThxBHBr-SMe2, in methylene chloride is birthday. very stable and no disproportionation or loss of hydride is ob- 314 Bull. Korean Chem. Soc., Vol. 8, No. 4, 1987 Jin Soon Cha et 시 . Table 1. Reaction of Thexylbromoborane-Methyl sulfide with Ta비 e 3. Stereochemistry o£ Cyclic Ket이 * Reduction with Representative Active Hydrogen Compounds in Methylene ThxBH2, ThxBHCl> ThxBHBr in Methylene Chloride Chh>퍼 de at 0°C c , Less Stable Iscmer(%>m , Reduction time hydrogen hydride hydride used compound compound41 Temperature _ (hr) evolved6-17 used* for reduction ThxBH/ ThxBHCK ThxBHBk 1-hexanol 0.5 0.97 0.97 0.00 0 47-50 94.5 97.5 1.0 0.97 0.97 0.00 Q=o -23 96.5 98.5 benzyl alcohol 0.5 1.06 1.06 0.00 0 1.0 1.08 1.08 0.00 68.5 80.5 -23 69.5 86 3-hexanol 0.5 0.95 0.95 0.00 V 1.0 0.95 0.95 0.00 0 56.5 3-ethyl-3-pentanoI 0.5 0.97 0.97 0.00 o° -23 58 79 1.0 0.98 0.98 0.00 0 65.5 78.5 phenol 0.25 0.93 0.93 0.00 K>° -23 66 86 0.5 0.97 0.97 0.00 0 92 1.0 1.01 1.01 0.00 98.5 99 -23 99.9 99.6 w-hexylamine 12.0 0.00 0.00 0.00 1-hexanethiol 12.0 0.00 0.00 0.00 H지 Ketone = 2:1. b Quantitative Yields.c In THF. d In CH2C12. a 3.0 Mmole of compound to 12 mmole of ThxBHBr SMe2(12 mmole of hydride) in 12.0 m/ of solution; 0.25 M in compound and 1.0 M in Results and Discussion hydride. b Mmole/mmole of compound. c Hydrogen evolved from blank minus the hydrogen evolved on hydrolysis of the reaction mix­ ture after the indicated reaction period. Procedure for Rate and Stoichiometry Studies. Thexylbromoborane-methyl sulfide was prepared from the hydroboration of 2,3-dimethyl-2-butene (tetramethylethy­ Table 조 . Reaction of Thexylbromoborane-Methyl Sulfide with lene) with monobromoborane-methyl sulfide, which was pre­ Representative Aldehydes and Ketones in Methylene Chloride pared by reaction of borane-methyl sulfide (BMS) with a half atO°C equiv of bromine4, in methylene chloride. The reagent was time hydrogen hydride hydride used stable at 0°C at least for 3 months. The procedure for the compound4 (hr) evolved 皈 used* for reduction皈 systematic study involved preparation of a reaction mixture of the reagent (1.0M in hydride) and the compound examined caproaldehyde 0.5 0.00 0.90 0.90 (0.25 M) under study in methylene chloride at 0°C. Hy­ 1.0 0.00 1.01 1.01 drogen evolution during the reaction was measured by using benzaldehyde 0.5 0.00 0.84 0.84 a gas-buret. A blank test under identical conditions, but with­ 1.0 0.00 0.96 0.96 out the compound, was accompanied. At the appropriate 3.0 0.00 1.01 1.01 reaction intervals, aliquots were withdrawn from the reaction 2-heptanone 1.0 0.00 0.60 0.60 mixture and analyzed for residual hydride by hydrolysis5. 3.0 0.00 0.99 0.99 From the difference in the volume of hydrogen evolution in 6.0 0.00 0.99 0.99 the two cases, the hydride used by the compound for reduc­ norcamphor 1.0 0.00 0.90 0.90 tion was calculated. In this way, it was possible to calculate a 3.0 0.00 1.01 1.01 value for the number of moles of the hydride consumed by 6.0 0.00 1.01 1.01 the compound to 은 volve hydrogen and the number of moles acetophenone 0.5 0.00 0.98 0.98 of hydride utilized for the reduction5. 1.0 0.00 1.02 1.02 Alcohols, Amines, and Thiols (Active Hydrogen Com­ benzophenone 9.0 0.00 0.44 0.44 pounds) Of those active hydrogen compounds examined, 12.0 0.00 0.58 0.58 alcohols evolved 1 equiv of hydrogen rapidly and quan­ 36.0 0.00 0.78 0.78 titatively in less than 1 h. However, n-hexylamine and 1-hex­ 48.0 0.00 0.78 0.78 anethiol did not evolve any hydrogen under these conditions. 72.0 0.00 0.98 0.98 The rate of reaction of ThxBHBr SMe2 with active hydrogen cinnamaldehyde 0.5 0.00 1.04 1.04 compounds studied is a little slower than that of ThxBHCL 1.0 0.00 1.24 1.24 SMe} These results are summarized in Table 1. 3.0 0.00 1.40 1.40 Aldehyde and Ketones. Of those aldehydes and ke­ a-。See corresponding:footnote in Table 1. tones studied, the les오 hindered compounds consumed 1 equiv of hydride for reduction rapidly within 1 or 3 h, whe- served while the reagent is kept at 0°C. In order to inves­ areas the more hindered ketones such as benzophenone re­ tigate the reducing characteristics of the reagent, we under­ quired 3 days for complete reduction. This also indicates that took the systematic study on the approximate rate and stoi­ thexylbromoborane is a much weaker reducing agent than chiometry for the reaction of excess thexylbromoborane- the chloro-derivative.
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