- The Hydroboration of Silylacetylenes. The "Silyl-Markovnikov" Hydroboration Route to Pure (Z)-1-(2-Borylvinyl)silanes and β-Keto Silanes
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The regiochemistry and stoichiometry of the hydroboration of simple 1-silylacetylenes with 9-borabicyclononane (9-BBN) was examined in detail. (Trimethylsilyl)acetylene (1c) results in only β-mono- and dihydroboration products, behavior common to nonsilylated terminal acetylenes.It is less reactive than its alkyl counterparts toward 9-BBN.It was also demonstrated that (1-trimethylsilyl)alkynes form (α-borylvinyl)silanes, similar to 1-alkynes, but they are much less reactive.Clean monohydroboration of these silylacetylenes is achieved only with a bulky (e.g. t-Bu) group at the C-2 position.However, compared to 1-alkynes, their dihydroboration products differ markedly, with the former giving 1,2-diboryl compounds, while the latter results in 1,1-diboryl adducts. (Triethyl- and tert-butyldimethylsilyl)propynes exhibit similar reactivity to that of the analogous trimethylsilyl derivative.The triisopropylsilyl group was found to not only completely suppress dihydroboration but also gave exclusively (Z)-(β-borylvinyl)silane adducts (9β).Oxidation of 9β produces the corresponding β-keto silanes (12) in excellent yields (i.e. 83-90percent).The bulky (triethyl- and tert-butyldimethylsilyl)propyne hydroboration products were found to be thermally unstable with the initially formed (α-borylvinyl)silanes isomerizing to α/β mixtures through their 1,2-diboryl diadducts (10).Heating 10 produces (3,3-diborylpropyl)silanes (14).Oxidation of the triethylsilyl compound 14b affords the corresponding γ-silylpropanol (15b).The complete characterization of the intermediate organoboranes by 75-MHz 13C NMR was achieved.A detailed discussion of the phenomena involved is presented.The observed results are attributed primarily to the additional steric effects imposed on an unsaturated system by a trialkylsilyl group when compared to a hydrogen atom at that position.
- Soderquist, John A.,Colberg, Juan C.,Valle, Luis Del
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- Efficient preparation of the 18-methoxycoronaridine side-chain precursor
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An efficient synthesis of the side-chain precursor crucial to the preparation of 18-methoxycoronaridine (18-MC) has been developed. This procedure represents an improvement upon the original synthesis, in which regioisomers were separated by chromatography to provide the requisite precursor. Incorporation of the protected primary alcohol moiety in the early stages of the synthesis provides the requisite regioisomer unambiguously and obviates the need for chromatography at any point. Georg Thieme Verlag Stuttgart.
- Rainka, Matthew P.,Dowling, Matthew S.,King, Chi-Hsin R.,Meckler, Harold,Herr, R. Jason
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p. 2743 - 2747
(2008/02/05)
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- ORGANOBORANES FOR SYNTHESIS.9. RAPID REACTION OF ORGANOBORANES WITH IODINE UNDER THE INFLUENCE OF BASE. A CONVENIENT PROCEDURE FOR THE CONVERSION OF ALKENES INTO IODIDES VIA HYDROBORATION
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The reaction of organoborane with iodine is strongly accelerated by sodium hydroxide.Organoboranes derived from terminal alkenes react with the utilization of approximately two of the three alkyl groups attached to boron, providing a maximum of 67percent yield of alkyl iodide.Thus, hydroboration-iodination of 1-decene gives a 60percent yield of n-decyl iodide.Secondary alkyl groups, derived from internal alkenes, react more sluggishly and only one of the three alkyl groups attached to boron is converted to the iodide.Thus, the procedure applied to 2-butene provides a 30percent yield of 2-butyl iodide.The use of disiamylborane bis-(3-methyl-2-butylborane, Sia2BH as hydroborating agent increases the yield of iodides from terminal alkenes since the primary alkyl groups react in preference to the secondary siamyl groups.Consequently, hydroboration of 1-decene with Sia2BH, followed by iodination gives a 95percent yield of n-decyl iodide.The use of methanolic sodium methoxide in place of sodium hydroxide provides alkyl iodides in considerably higher yields.The combination of hydroboration with iodination in the presence of a base provides a convenient method for the anti-Markovnikov hydroiodination of alkenes.The base-induced iodination of organoboranes proceeds with the inversion of configuration at the reaction center, as shown by the formation of endo-2-iodonorbornane from tri-exo-norbornylborane.
- Brown, Herbert C.,Rathke, Michael W.,Rogic, Milorad M.,de Lue, Norman R.
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p. 2751 - 2762
(2007/10/02)
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- Organotin-containing composition for the stabilization of polymers of vinyl chloride
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An organotin-containing composition for the stabilization of polymers or copolymers of vinyl chloride in which there is incorporated a stabilizing amount of an organotin compound containing at least two tin atoms and which is a mercapto, hydroxy or alkoxy substituted ester of a mercapto acid substituted organotin mercapto acid diester.
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- Hydroboration. 67. Cyclic Hydroboration of Acyclic α,ω-Dienes with 9-Borabicyclononane/Borane-Dimethyl Sulfide
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Hydroboration of acyclic α,ω-dienes, 1,3-butadiene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, 1,8-nonadiene, 1,9-decadiene, 1,11-dodecadiene, and 1,13-tetradecadiene, with 2 molar equiv of 9-borabicyclononane (9-BBN), followed by redistribution of the resulting dumbbell-shaped trialkylboranes with 1 molar equiv of borane-methyl Sulfide complex (BMS), has been investigated.With 1,3-butadiene, the initial redistribution product, the five-membered boracyclane, borolane, underwent a rapid ring-opening reaction to give the known 1,6-diboracyclodecane. 1,4-Pentadiene and 1,5-hexadiene afforded the corresponding boracyclanes, borinane and borepane, in quantitative yields.With all other dienes, the initial redistribution products were polymeric.They were converted to the methyl esters by treatment with methanol, and these products were depolymerized into cyclic derivatives in 88-98percent yield by vacuum distillation at 175-200 deg C.In every case the cyclization was accompanied by varying amounts of isomerization so that the major products were both the parent B-methoxyboracyclane and the corresponding B-methoxy-2-n-alkylborinane.Thus, 1,6-heptadiene afforded B-methoxyborocane and B-methoxy-2-ethylborinane in 3:1 ratio and a total yield of 95percent.With 1,7-octadiene, 1,8-nonadiene, 1,9-decadiene and 1,11-dodecadiene, the isomerized product constituted the major constituent of the distillate. 1,13-Tetradecadiene afforded the parent boracyclane and the isomer in a 47:53 ratio and a combined yield of 82percent.The B-methoxyboracyclanes were converted to the corresponding cyclic ketones by the DCME reaction in 55-65percent yield.
- Brown, Herbert C.,Pai, Ganesh G.,Naik, Ramachandra G.
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p. 1072 - 1078
(2007/10/02)
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- SYNTHESE A L'AIDE DE SULFONES-XXVI. SYNTHESE D'ALCOOLS ALLYLIQUES ET DE POLYPRENOLS PAR ATTACHEMENT D'UN SYNTHON PRENOL EN POSITION 4 E
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The E-hydroxyalkylsulphone PhSO2CH2C(CH3)=CHCH2OH is regioselectively and stereoselectively substituted by Grignard reagents in the presence of copper(II) acetylacetonate, giving E allylic alcohols in high yield.A recurrent synthesis of polyprenols and an efficient preparation of the African Monarch pheromone are described.
- Julia, Marc,Verpeaux, Jean-Noel
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p. 3289 - 3292
(2007/10/02)
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- Oxymetallation. Part 13. Synthesis of Bicyclic Peroxides via Peroxymercuriation of Cyclic Dienes
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The bis-mercuriated derivative (12) of 9,10-dioxabicyclodecane has been prepared by peroxymercuriation of cis,cis-octa-1,5-diene, but substantial amounts of bicyclic ethers are also formed in the reaction.The bicyclic peroxides (4) and (5) have been obtained from (12) by reduction and brominolysis respectively. 8,9-Dioxabicyclodecane (6) and the dibromo-derivative (7) have similarly been prepared by peroxymercuriation and demercuriation of cyclo-octa-1,4-diene.It is suggested that the isomeric purity of the peroxides and the concurrent formation of bicyclic ethers both result from equilibrium control of reversible (per)oxymercuriation-de(per)oxymercuriation.A low yield of the -peroxide (8) has been obtained by peroxymercuriation and brominolysis of cyclohexa-1,4-diene, but attempts to prepare -compounds from 5,5-disubstituted cyclopentadienes have been unsuccessful.
- Bloodworth, A.J.,Khan, Jamil A.,Loveitt, M.E.
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p. 621 - 632
(2007/10/02)
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- Cyanidation Products of Organoboranes Derived from Linalyl Acetate
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The seven-membered cyclic borane obtained from the reaction of linalyl acetate and thexylborane loses 2,3-dimethylbut-2-ene, and the resulting dialkulborane gives an alcohol on treatment with sodium syanide, followed by trifluoroacetic anhydride and oxidation.The structure is confirmed by synthesis.The generality of this reaction was investigated but, of the dialkylboranes examined, only 9-borabicyclononane participated in the cyanidation procedure.A simple synthesis of menthone is presented
- Murphy, Roger,Prager, Rolf H.
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p. 143 - 150
(2007/10/02)
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- Hydroboration. 56. Convenient and Regiospecific Route to Functionalized Organosilanes through the Hydroboration of Alkenylsilanes.
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A systematic and detailed study of the hydroboration of several representative alkenylsilanes is reported.By use of a 1:1 molar stoichiometry, the hydroboration of vinyltrimethylsilane (1) at 0 deg C with BH3*THF gives a mixture of dialkylborane products exclusively with a ca. 60:40 distribution of a α- and β-silylethyl groups in these adducts.Redistribution of the reaction mixture at a somewhat higher temperature (50 deg C) gives the corresponding monoalkylboranes.The redistribution process is regiospecific, leaving the original 60:40 ratio of α- and β-silylethyl groups in the dialkylboranes unchanged in the monoalkylboranes produced.With a 3:1 ratio of 1 to BH3*THF, equimolar amounts of dialkyl- and trialkylborane products are formed in the hydroboration reaction.Under these conditions, the α to β ratio changes modestly to 50:50.The failure of the hydroboration to attain complete conversion to the trialkylborane stage is attributed largely to the low reactivity of meso-bisborane produced in the reaction in the further hydroboration of 1.The change in the regioselectivity from 60:40 to 50:50 with a 3:1 stoichiometry is attributed to the higher β selectivity of dialkylboranes in the hydroborationof 1.Thus, the hydroboration of 1 with 9-borabicyclononane (9-BBN) is regiospecific, giving exclusively the B--9-borabicyclononane (3) product.Redistribution of 3 with BH3*THF gives essentially complete conversion to 9-BBN and pure bisborane.This compound hydroborates 1 rapidly at 0 deg C, giving predominantly (ca. 85percent) the β adduct, trisborane.Hydroboration of propen-2-yltrimethylsilane with BH3*THF gives primarily (91percent) β boron placement.However, use of 9-BBN eliminates the formation of the minor internal product and gives (2-Me3Si-1-Pr)-9-BBN exclusively.Hydroboration of cis-1-propenyltrimethylsilane (17) with BH3*THF proceeds to the dialkylborane stage, with no significant formation of the corresponding trialkylborane.The hydroboration is highly regioselective, giving the bisborane product in 95percent regioisomeric purity.This borane is unusual in that it is monomeric in solution, as revealed by IR and 11B NMR data.Hydroboration of 17 with 9-BBN is much less selective than that with BH3*THF, a rare occurrence, giving essentially equal amounts of regioisomeric adducts.Hydroboration of allyltrimethylsilane with either BH3*THF or 9-BBN gives the (γ-silylpropyl)borane product exclusively.Hydroboration of 3-buten-1-yltrimethylsilane with BH3*THF gives the (δ-silylbutyl)borane adduct in 94percent isomeric purity.With 9-BBN, the hydroboration is regiospecific, giving the (δ-silylbutyl)borane adduct exclusively.Thus, through hydroboration, the syntheses of α, β, γ, and δ boron-functionalized organosilanes are achieved, making such compounds available for use as synthetic intermediates.The 13C and 11B spectra...
- Soderquist, John A.,Brown, Herbert C.
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p. 3571 - 3578
(2007/10/02)
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