Chloroboranes

Chloroboranes have also been found useful for enantioselective reduction. Di-(isopinocampheyl)chloroborane,144 (Ipc)2BCl, and /-butyl (isopinocamphcylj... 

Table 5.5 gives some typical results for enantioselective reduction of ketones by alkylborohydrides and chloroboranes. 

The sulfoxide directed reduction of olefin is known, so is sulfoxide reduction by chloroborane, but not simultaneous reduction of both by borane. 

Inasmuch as trimethylsilylamine is unstable, it will decompose into ammonia and hexamethyldisilazane. The ammonia thus formed could be visualized to form the amino compound (MegSi)2NB(NHg)-NHSiMe. Since (MegSi) NB(NHSiMe3)2 was prepared Zby Wells and Collins (.13) via Interaction of5 tne chloroborane with hexamethyldisilazane, its production here could follow the same path. 

The same event is true for the reaction of chlorocyanide with n-buthyldichloroborane and di(n-butyl)chloroborane respectively 24) (c.f. Eq. (23) for the reaction of bromocyanide). 

Independent preparation of the same materials (by 1,2-addition of butyldi-chloroborane and dibutylchloroborane respectively 2S)) to chlorocyanide confirms the suggested structures. 

There is some evidence for cyclic iminoboranes as intermediates. When cyclic chloroboranes react with Me3SiN3 at room temperature (i.e., the normal route for attaching an N3 group to boron), evolution of N2 is observed and one of the products of Eqs. (13) and (14) is isolated. 

The chloroborane reactants of Eqs. (13) and (14) can be aminated to isolable [silyl(silyloxy)amino]boranes, which decompose at 120 and 70°C, respectively, to give a mixture of products, three of which were identified in both cases [Eqs. (15) and (16)] (19). Again, the iminoboranes... 

The aminoiminoborane Me3Si—(tBu)N—B= Nnovel synthesis for diazadiboretidines. Addition of chloroboranes RjBCl with smaller R groups (R = Me, Et, Pr, iPr) proceeds directly to the diazadiboretidine, the primary addition product not being isolable. 

Cleavage of hydroperoxides 8-25 Treatment of boranes with CO and H20, followed by NaOH and H202 or with CN followed by trifluo-roacetic anhydride from dialkyl-chloroboranes... 

B-Bromo and B-iodo-9-borabicyclo[3.3.1]nonane add similarly in a cis fashion to terminal triple bonds 471 They do not react, however, with alkenes and internal acetylenic bonds. In contrast to the results mentioned above, phenyl-substituted chloroboranes (PhBCl2, Ph2BCl) do not participate in haloboration. Instead, the C—B bond adds across the multiple bond to form phenylalkyl-(alkenyl) boranes.466,468... 

Isocyanates may be prepared via a number of routes, including the thermal cracking of urethanes or silylurethanes [107], or the reaction of N-alkylcarbamate esters with boron trichloride [108] or chloroboranes [109] or chorosilanes [110] in the presence of bases (NEt3). To date, however, only amine phosgenation is practiced on a significant industrial scale [10, 106],... 

Weber and coworkers reported the synthesis of novel substituted borazoles. The reaction of boron trichloride with 1,2-diimines 367 provide a mixture of products. The formation of dimeric borazole 369 was explained based on a nucleophilic attack of the chloroborane 370 on the ate complex 368 followed by dehydrohalogenation. Alternatively, a controlled addition of BCR to the diimine 367 results in a clean formation of the imine-borane complex 373 that upon reduction with sodium amalgam and calcium hydride provided the chloroborazole 375 (Scheme 59) <2006EJI5048>. 

The stereoselectivities of the carbonyl group reductions with Alpine-Borane (Figure 10.24) or with Brown s chloroborane (Figure 10.25) are explained as shown in the for-... 

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