Boranes reaction with aminals

Imamoto reported that Pd-catalyzed coupling of phosphine-borane with aryl halides is useful for preparation of asymmetric phosphines. Phosphines can be easily isolated from phosphine-boranes by exchange reaction with amines such as pyrrolidine and DABCO [10]. Lipshutz found that aryl nonaflates ( Nf = nonafluorobutanesulfonate) and triflates are good substrates for coupling with BHs-stabilized diaryIphosphines. Selective coupling with nonaflate without... 

The desired pyridylamine was obtained in 69 % overall yield by monomethylation of 2-(aminomethyl)pyridine following a literature procedure (Scheme 4.14). First amine 4.48 was converted into formamide 4.49, through reaction with the in situ prepared mixed anhydride of acetic acid and formic acid. Reduction of 4.49 with borane dimethyl sulfide complex produced diamine 4.50. This compound could be used successfully in the Mannich reaction with 4.39, affording crude 4.51 in 92 % yield (Scheme 4.15). Analogous to 4.44, 4.51 also coordinates to copper(II) in water, as indicated by a shift of the UV-absorption maximum from 296 nm to 308 nm. 

Properties and Reactions. Amine boranes are usually colodess, crystalline compounds, which exhibit sharp melting points and thermal stability when pure. Primary and secondary amine boranes are generally soHds at ambient temperatures. With the exception of trimetbylamine borane, the ahphatic /-amine boranes are Hquids. The nature of the bonding in amine boranes has been the subject of theoretical investigations (21—23). 

A more convenient high-yield synthesis of Bi2Hi2 is by the direct reaction of amine-boranes with BiqHu in the absence of solvents ... 

Amine-borane complexes are not very reactive toward hydroboration, but the pyridine complex of borane can be activated by reaction with iodine.160 The active reagent is thought to be the pyridine complex of iodoborane. 

The reaction between a Lewis acid R3M and a Lewis base ER3 is of fundamental interest in main group chemistry. Synthetic and computational chemists have investigated the influence of both the Lewis acid and the base on the solid state structure and the thermodynamic stability of the corresponding adduct, that is usually expressed in terms of the dissociation enthalpy De. This led to a sophisticated understanding of the nature of dative bonding interactions. In particular, reactions of boranes, alanes and gallanes MR3 with amines and phosphines ER3, typically leading to adducts of the type R3M <— ER3, have been studied.10... 

One of the novel exiting developments in the field of tin-free radical chain reactions is the development of complexes of borane with NHCs as HAT reagents [6]. Borane (BH3) itself has a BDE of 106.6 kcal mol 1 which is much too high for its use in organic radical chain reactions. The group of Roberts and others have demonstrated that complexes of boranes with amines and phosphines have a reduced BDE and that they can be used in radical chain reactions [7]. However, the reduction is only moderate and too low to make these complexes generally applicable. 

Tris(organoamino)boranes have been utilized to prepare, in reasonable yields,4,5 mono- and dihalo(organoamino)boranes which are often difficult to obtain by direct amination of the boron trihalides. Carboxylic acids, 1,3-diketones, ketones, and /3-ketoesters have been converted into carboxamides, enamino-ketones, enamines, and j -enamino-amides, respectively, by reaction with an appropriate tris(organoamino)borane under very mild conditions.6 Sulfenamides (R2NSC6H5) have also been prepared in high yield from selected tris(organoamino)boranes and sulfenic esters under relatively mild conditions.7... 

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