Diborane 1-methyl

C. 4-Methyl-1-pentanol from 4-Methyl-1-pentene In Situ Generation of Diborane in Tetrahydrofuran (3)... 

In a 200-ml three-necked flask fitted with a dropping funnel (drying tube) is placed a solution of 13.4 g (0.12 mole) of 1-octene in 35 ml of THF. The flask is flushed with nitrogen and 3.7 ml of a 0.5 M solution of diborane (0.012 mole of hydride) in THF is added to carry out the hydroboration. (See Chapter 4, Section I regarding preparation of diborane in THF.) After 1 hour, 1.8 ml (0.1 mole) of water is added, followed by 4.4 g (0.06 mole) of methyl vinyl ketone, and the mixture is stirred for 1 hour at room temperature. The solvent is removed, and the residue is dissolved in ether, dried, and distilled. 2-Dodecanone has bp 119710 mm, 24571 atm. (The product contains 15 % of 5-methyl-2-undecane.) The reaction sequence can be applied successfully to a variety of olefins including cyclopentene, cyclohexene, and norbornene. 

A mixture of d- and l- hexoses also results from the hydroboration of these 5-enes. Hydroboration results in anti-Markownikoff, cw-hydration of the double bond and the amount of each hexose formed varies according to the nature of the substituent groups. For example, hydroboration (23) of methyl 6-deoxy-a-D-ryZo-hex-5-enopyranose (3) affords methyl a-D-glucopyranoside and methyl / -L-idopyranoside in the ratio of 1 2.5 respectively whereas hydroboration of the fris-trimethylsilyl ether of 3 afforded them in the ratio 1 0.6 respectively. The hydroboration method can be used to achieve specific labelling of hexoses with tritium methyl-/ -L-idopyranoside[5-H3] and methyl a-D-glucopyranoside [5-H3] were thus prepared (23). Similarly, hydroboration of the D-Zt/ro-hex-5-eno derivative (14) with diborane-H3 followed by removal of the isopropyli-dene group, afforded methyl a-D-mannopyranoside [5-H3] and methyl / -L-gulopyranoside [5-H3] in the ratio of 1 2 respectively (23). 

Natrium- und Kaliumboranat konnen als Pulver gefahrlos zur Reaktionsmischung ge-geben werden Lithiumalanat, Diboran und Bis-[2-methyl-propyI]-aIuminiumhydrid werden als Ldsungzugetropft oder mit einer Injektionsspritze eingegeben (s.z.B. S. 226 u. S. 233). 

Mit Diboran bzw. Bis-[3-methyl-butyl-(2)]-boran in THF werden bei -5bis0°43-52bzw. 74% d. Th. Diphe-... 

Mit neun Hydrid-Aquivalenten Diboran erhalt man als Hauptprodukt 3-Hydroxy-2-methyl-4-hydroxymethyl-pyridin-5-carbonsaure-4 -lacton2 ... 

Mit Diboran verlauft die Reaktion in THF oder Bis-[2-methoxy-athyl]-ather ahnlich12, 13. Mit dieser Methode konnen auch N-Methyl-Verbindungen hydrogenolytisch umge-setzt werden (2-Formyl-pyrrol polymerisiert13) z.B. ... 

Wahrend Natriumboranat und Diboran Sulfonyl-Gruppen nicht angreifen, erhalt man mit Bis-[2-methyl-propyl]-aluminiumhydrid unter energischen Bedingungen Sul-fane. Die Reaktion wird in Toluol oder Mineralol durchgefiihrt. Zur Reduktion geniigen drei Hydrid-Aquivalente z.B. ... 

As mentioned above (Scheme 3), condensation of triallylborane and 3-methoxybut-l-yne led, after treatment with methanol, to 7-(l-methoxymethyl)-3-methoxy-3-borabicyclo[3.3.1]non-6-ene. Hydroboration-isomerization of the latter with a THF solution of diborane gave a THF complex of 2-methyl-1-boraadamantane 15 in 85% yield. Treatment of the latter with (S)-(—)-phenylethylamine gave a mixture of diastereomeric complexes ( ) 57 isolated as white, well-shaped crystals (Scheme 19) <2003MC121, B-2003MI97>. 

The rhodium-catalyzed borylation of methyl C-H bonds is compatible with several moieties containing oxygen, nitrogen, and fluorine.154 For example, the reaction of pinacol acetal of 2-hexanone with bis(pinacolato)diborane (B2pin2) in the presence of Cp Rh(774-C6Me6) catalyst gives the alkylboronate ester in 74% yield (Equation (111)). The rhodium-catalyzed C-H activation and borylation occur at the least hindered and least electron-rich methyl group. 

Enantioselective reduction of ketones.1 The ability of diborane in combination with the vic-amino alcohol (S)-2-amino-3-methyl-l,l-diphenyl-l-butanol (12, 31) to effect enantioselective reduction of alkyl aryl ketones involves formation of an intermediate chiral oxazaborolidine, which can be isolated and used as a catalyst for enantioselective borane reductions (equation I). 

Potassium borohydride also may be prepared by reacting potassium tetramethoxyborohydride with diborane at low temperatures or by passing diborane through a solution of potassium methylate in methanol. 

Also, sodium borohydride can be made by passing diborane, B2H6, through a solution of sodium methylate, NaOCH3, in methanol ... 

In gleicher cheraischer Ausbeute, jedoch mit einer optischen Ausbeute von 76%, laBt sich Acetophenon-(O-methyl-oxim) mit Lithium-alanat in Gegenwart eines aus Diboran und (S)-2-Amino-3-methyl-l,l-diphenyl-butanol gebildeten Boran-Adduktes zu (S)-l-Amino-1-phenyl-ethan reduzieren2. 

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