Chloramine reaction with trialkylboranes

The reaction of trialkylboranes with iV-chloroalkylamines can be used to synthesize a wide variety of functionally substituted dialkylamines in good yields [66,67], and it complements the synthesis of secondary amines via the reaction of trialkylboranes with organic azides. The reaction is analogous to the reaction of chloramine with organoboranes, and presumably occurs via an anionotropic migration of an alkyl group from boron to nitrogen (Scheme 24). 

Enantiopure benzylamines are important intermediates in the synthesis of pharmaceutically active compounds and chiral ligands for asymmetric transformations. Fernandez and co-workers ° reported that primary and secondary benzylamines could be obtained in moderate yields by converting the initially formed catecholboronate ester into a trialkylborane by reaction with either diethylzinc or methylmagnesium chloride, followed by treatment of the trialkylborane thus obtained with hydroxylamine-O-sulfonic acid, which yielded primary benzylamine 291. When the trialkylborane was treated with A-substituted chloramines, a secondary benzylamine, e.g., 292, was formed. A variety of vinylarenes gave the corresponding benzylamines in moderate to good yields and good-to-excellent enantioselectivity (78-98% ee). 

Several papers have appeared describing the synthesis of alkyl halides from organoboranes. Alkyl chlorides are obtained by the reaction of trialkylboranes with dichloramine-T, and in somewhat lower yield with iV,N-dichlorourethane/ whereas alkyl bromides are produced in excellent yield when the boranes derived from terminal alkenes and dicyclohexylborane are treated with either Bt2 or BrCl. Alkyl iodides are obtained from the same boranes by the use of ICl-NaQAc " or iodide ion-chloramine-T/ and this latter method has been applied to the radioiodination of olefins (with Vinyl iodides result from... 

The reaction of trialkylboranes with lead(iv) acetate or phenyliodosoacetate to yield the corresponding alkyl acetate has been described as has the reaction of trialkylboranes or 5-alkyl-9-BBN derivatives with JV-substituted 2-lithioindoles to give, after iodination, 2-alkylindoles. It has also been reported that trialkylboranes react with chloramine-T and its analogues to produce A-substituted sulphonamides [reaction (5)]. ... 

After hydroboration, oxidation of radioiodide is performed with Chloramine-T, forming HO-I, which then adds to the C-B bond. The reactivity of the C-B bonds depends on the position of boron, which can either be formed from a terminal double bond or from an internal alkene. While the former case produces two radioiodinated compounds, the latter forms only one. Therefore, dicyclohexylborane is used for the hydroboration step. Both reactions, hydroboration of the alkene and radioiodination can be performed in one sequence without isolating the intermediately formed trialkylborane. 

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