Monochloroborane diethyl etherate

The products are Hquids, soluble in various solvents and stable over prolonged periods. Monochloroborane is an equiUbtium mixture containing small amounts of borane and dichloroborane complexes with dimethyl sulfide (81). Monobromoborane—dimethyl sulfide complex shows high purity (82,83). Solutions of monochloroborane in tetrahydrofuran and diethyl ether can also be prepared. Strong complexation renders hydroboration with monochloroborane in tetrahydrofuran sluggish and inconvenient. Monochloroborane solutions in less complexing diethyl ether, an equiUbtium with small amounts of borane and dichloroborane, show excellent reactivity (88,89). Monochloroborane—diethyl etherate [36594-41-9] (10) may be represented as H2BCI O... 

Although several monoalkylchloroboranes have been prepared by the 1 1 reaction of an alkene with monochloroborane-diethyl ether (see Section 3.10.3.2), almost the only one to receive detailed investigation is thexylchloroborane. This reagent is most useful as its dimethyl sulfide complex, prepared according to equation (45)" or equation (46), ... 

HYDROBORATION Bis(3,6-dimethyl)bore-pane. Bis(trans-2-methylcyclohexyl)bo-rane. Catecholborane. Dicyclohexylbo-rane. Diisopinocamphenylborane. 2,3-Dimethyl-2-butylborane. Dimethyl sul-fide-Borane. Monochloroborane-Diethyl etherate. 

DCBS is highly regioselective, exhibiting the directive effects similar to those observed for monochloroborane diethyl etherate. Alkyldichloroboranes are readily isolated by distillation under vacuum. Methanolysis provides the corresponding alkyl-boronic esters (eq 2). Alkenylboronic esters can be obtained from alkynes (eq 3). ... 

The early literature associated with monochloroborane hydroborations contains errors and it is probably appropriate to ignore publications prior to about 1970. Monochloroborane complexes THE more strongly than does borane and this slows down its reactions with alkenes in this solvent. Thus, other reactions may compete and mixtures may result. The diethyl ether complex is weaker and hydroborations... 

The reactions of monochloroborane in diethyl ether with a,(o-dienes lead initially to mixtures which are partially polymeric and possibly composed of different ring sizes. However, careful distillation can lead to both depolymerization and isomerization, so that in several cases a single cyclic product can be obtained (e.g. Scheme 5). ... 

If alkyldichloroboranes are specifically required, dichloroborane-dimethyl sulfide is the reagent of choice. It is more stable and more convenient than the dichloroborane-diethyl ether complex, but its hydroborating properties are very similar." Dichloroborane complexes ethers even more strongly than monochloroborane, and its reactions with alkenes in this solvent are slow and lead to mixtures. Therefore, it is generally used in pentane and trichloroborane is added to liberate uncomplexed dichloroborane. Under these conditions it readily gives alkyldichloroboranes on reaction with alkenes or alkenyldichloro-boranes on reaction with alkynes. " " The latter reaction has been applied to alkynylsilanes (equation 44)." ... 

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