Borane imino

However, the successful isolation of an iminoborane derivative in the reaction of trichloroacetonitrile with diborane indicated that the stability of imino-boranes is not only a function of the nature of the borane but also of that of the imine 16>. 

Due to difficulties in separating (VII) from the IiCl byproduct, it was found to be advantageous to prepare (VII) by the reaction of a tris(imino)borane with trifluoroborane-etherate as illustrated in Eq. (26). 

Bis(imino)haloboranes, however, were found to be unstable with respect to rearrangement into (imino)dihaloboranes and tris(imino)borane also, utilization of more than one equivalent of (C6H5)C=N—Si(CH3)3 converts trihaloboranes to mixtures of mono- and tris(imino)boranes which are the final products depending upon the ratio of starting materials. 

For a compilation of iminoboranes derived from haloboranes and organohaloboranes see Table 4. However, aldiminoboranes are listed in Table 3 and sulfur-containing compounds in Table 7. Bis- and tris(imino)boranes are listed in Table 6. 

It is apparent that the B-N bond in imine-borane adducts is not very strong and is influenced by the donor and acceptor properties of the components as well as by steric factors. In the infrared spectra of the adducts the ON stretching bands show only slight shifts as compared with those of the free imino derivatives 23>44). 

Reactions of the type in Eq. (42) have been achieved with aldehydes and ketones [Eq. (43)] (9, 19). None of the intermediates according to Eq. (42) was isolated. A [2 + 2]-cycloaddition (step a) probably occurs, since [2 + 2]-cycloadducts can be isolated from the reaction of imino-boranes and oxoalkanes in particular cases (Section VI,A). As far as alkynes are concerned, addition of oxo compounds proceeds in the presence of BFj as a catalyst, but without a break of the CC <7-bond [in analogy to step c in Eq. (42)] rather polar alkynes are needed [Eq. (44)] (78). 

The two lactams obtained, 60 and 63, were silylated in situ followed by borane reduction to give the 2-amino-l,2,5-trideoxy-l,5-imino-D-xylitol (61), and 2-amino-l,2,5-trideoxy-l,5-imino-D-ribitol (64), respectively [79]. 

A further example of synthesis of the imidazo[4,5-rf [l,3,2]diazaborolidine ring system involving reaction between 4-imino-5-aminoimidazoles, analogous to 90, and boranes has been reported (see Section 10.05.9.1.2(viii)) <2006ZN(B)437>. 

Thus far we have seen that Schiff base ligands tend to promote six-coordination, but an unusual reaction has been found to occur between TiCl2(salen) and borohydride. No reduction at titanium is seen, but rather, addition of BtLr to the imino function of the ligand occurs to give a dimeric seven-coordinate titanium(IV) compound, (24), containing amine-boranes as... 

Interestingly we found that stannylboranes are also accessible by hydrostannylation of the amino imino borane tmp-B=NCMe3 as shown in Figure 4. 

Oxazolidines (53) are readily formed from aldehydes or ketones and ethanolamines they can be hydrolyzed with ease and show reactions that might be expected of the imino alcohol intermediate (54). Among these are the addition of Grignard reagentsand catalytic hydrogenolysis of the C—O Ixjnd (equation 28).This reaction is exothermic over Adam s catalyst in methanol but slower in acetic acid. Nickel and copper chromite are also effective but at higher temperatures and pressures,as is the case with palladium. The same cleavage occurs with LAH (unassisted)and with the borane-THF complex. ... 

C. C. Wang, S. Y. Luo, C. R. Shie, and S.-C. Hung, Metal trifluoromethanesulfonate-catalyzed regioselective borane-reductive ring opening of benzylidene acetals A concise synthesis of 1,4-dideoxy-l,4-imino-L-xylitol, Org. Lett., 4 (2002) 847-849. 

Further progress has been reported in the chemistry of CT X, -p -bonded systems. Full details of such systems stabilised by intramolecular coordination, as in, e.g., 334, have been described. The kinetically stable system 335 has been prepared and its solid state structure determined . The P-halobis(imino)-CT -phosphoranes 336 have also been prepared, and detailed NMR studies of bis(imino) phosphoranes reported . Quin s group has continued studies of the generation and characterisation of reactive a X -systems, e.g., 337 ". Methods for the generation of monomeric metaphosphate esters in solution have been investigated. A theoretical approach has been used to probe the mechanism of the reaction between phosphanylnitrenes 338 and boranes. The thiophosphonic anhydride 339 behaves as a source of the dithioxophosphorane... 

Aus (l-Butylthio-vinyloxy)-dibutyl-boran (hergeslellt aus Keten und Butylthio-dibutyl-boran)175 werden mit Carbonyl-Verbindungen bzw. Nitrilen176 nach anschlieBender Hydrolyse in sehr guten Ausbeuten 3-Hydroxy- bzw. 3-Imino-subst. Thiocarbonsaure-S-ester erhalten z, B.175 ... 

Basavaiah,D., Rao,K.V.and Reddy,B.S.(2006) (55)-l,3-Diaza-2-imino-3-phenylbicyclo[3.3.0] octane first example of guanidine based in situ recyclable chiral catal3dic source for borane-mediated as3munetric reduction of prochiral ketones. Tetrahedron Asymmetry, 17, 1036-1040. 

The second one involves highly stereoselective reduction of the 7-imino compound (88) with sodium cyanoborohydride under acidic condition at pH 3 in methanol, giving the 7P-isomer as the sole product in 90% yield [36]. The unique stereochemical outcome can be rationalized as follows. In an acid medium, sodium cyanoborohydride may produce a molecular complex of hydrogen cyanide and borane, HCN BH3, and this species reacts with either 7-methoxy amine (77) or 7-imine (88) to form (89) or (90), respectively. The methoxy-amine complex (89) may be converted into the imine-borane complex (90), which undergoes reduction with intramolecular hydride reduction either directly via (91) or more probably via a six-membered transition state (92). 

Asymmetric reductions of a-fiinctionalized ketones, such as a-hydroxy ketones, a-halo ketones, a-sulfonoxy ketones, 1,2-diketones, a-keto acetals or thio ketals, acyl cyanides and a-amino or imino ketones with boron-based chiral reducing agents in a stoichiometric or catalytic manner have been reviewed. The oxazaborolidine-catalyzed borane reduction of protected a-hydroxy ketones, a-keto acetals and a-sulfonoxy ketones has been discussed in more detail. 

Yamamoto and coworkers have also shown that tris(pentafluorophenyl)borane is a highly active catalyst for analogous imino-aldol reactions. Here, both the N-trialkylsilyl imines (72) (Equation 46) [44] and the N-benzyl imines (73) (Equation 47) [45] are applicable as electrophiles with ketene silyl acetals (74), and the reaction gives remarkably high yields of the N-benzyl imino-aldol adducts. 

The imino-substituted silylene features an N=C bond and a SieN bond however it may also be considered as an NHC-stabilized silylene—nitrene derivative (1) based on DFT calculations. The strongly electron-donating imidazolin-2-iminato as well as the Cp substituents may enhance the 5-donating ability of the iminosilylene. A silylene—borane adduct can be obtained by reacting the iminosilylene with BlCeFsls possessing significant 1-sila-2-azaallene character (1). 

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