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Diborane(6), commonly known as diborane, is the chemical compound with the formula B 2 H 6.It is a highly toxic, colorless, and pyrophoric gas with a repulsively sweet odor. . Given its simple formula, borane is a fundamental boron compou
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.
Diborane reacts with alkenes to give alkylboranes, a process known as hydroboration: B 2 H 6 + 2 CH 2 =CHR → 2 BH 2 (CH 2 CH 2 R) B 2 H 6 + 4 CH 2 =CHR → 2 BH(CH 2 CH 2 R) 2 B 2 H 6 + 6 CH 2 =CHR → 2 B(CH 2 CH 2 R) 2. Alkyl and aryl boranes can also be produced by alkylation of chloroboranes and boronic esters.
In general, if more than one alkene can be formed during dehalogenation by an elimination reaction, the more stable alkene is the major product. There are two types of elimination reactions, E1 and E2. An E2 reaction is a One step mechanism in which carbon-hydrogen and carbon-halogen bonds break to form a double bond. C=C Pi bond.
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.
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 ...
Ketene cycloadditions proceed by a concerted, [2+2] cycloaddition mechanism. Ketenes, unlike most alkenes, can align antarafacially with respect to other alkenes. Thus, the suprafacial- antarafacial geometry required for concerted, thermal [2+2] cycloaddition can be achieved in reactions of ketenes. [4]
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.