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4 BCl 3 + 3 LiAlH 4 → 2 B 2 H 6 + 3 LiAlCl 4 4 BF 3 + 3 NaBH 4 → 2 B 2 H 6 + 3 NaBF 4. When heated with NaBH 4, tin(II) chloride is reduced to elemental tin, forming diborane in the process: SnCl 2 + 2NaBH 4 → 2NaCl + Sn + B 2 H 6 + H 2. Older methods entail the direct reaction of borohydride salts with a non-oxidizing acid, such as ...
Without an additive, the reaction product is 2,3-dihydrofuran (2,3-DHF) and not the expected 2,5-dihydrofuran (2,5-DHF) together with the formation of ethylene gas. Radical scavengers, such as TEMPO or phenol, do not suppress isomerization; however, additives such as 1,4-benzoquinone or acetic acid successfully prevent unwanted isomerization.
Hydroboration of 1,2-disubstituted alkenes, such as a cis or trans olefin, produces generally a mixture of the two organoboranes of comparable amounts, even if the steric properties of the substituents are very different. For such 1,2-disubstituted olefins, regioselectivity can be observed only when one of the two substituents is a phenyl ring.
Thus, it is an intermediate in the preparation of diborane according to the reaction: [5] BX 3 +BH 4 − → HBX 3 − + (BH 3) (X=F, Cl, Br, I) 2 BH 3 → B 2 H 6. The standard enthalpy of dimerization of BH 3 is estimated to be −170 kJ mol −1. [6] The boron atom in BH 3 has 6 valence electrons.
[2] The complex can reduce carboxylic acids to alcohols and is a common route for the reduction of amino acids to amino alcohols [ 3 ] (e.g. valinol ). It adds across alkenes to give organoboron compounds that are useful intermediates. [ 4 ]
The metal-mediated processes include a carbonyl-olefination and an olefin–olefin metathesis event. There are two general mechanistic schemes to perform this overall transformation: one, reaction of a [M=CHR 1] reagent with an alkene to generate a new metal alkylidene, which then couples with a carbonyl group to form the desired substituted alkene and an inactive [M=O] species (type A); two ...
The reaction thus provides a more stereospecific and complementary regiochemical alternative to other hydration reactions such as acid-catalyzed addition and the oxymercuration–reduction process. The reaction was first reported by Herbert C. Brown in the late 1950s [2] and it was recognized in his receiving the Nobel Prize in Chemistry in 1979.
It then appears that the reaction proceeds mainly by a trans mechanism and, following the Zaitsev rule, 1-methylcyclohexene is preferentially formed in the early stages of the reaction. Indeed, if only about 10% of the total distillate is collected as the first fraction, one finds that the alkene is about 93% l-methylcyclohexene: at the end of ...