Trialkylboranes pyrolysis

The original procedure as reported by Goubeau and Zappel in their pioneering work B involves the pyrolysis of a mixture of trialkylborane and aliphatic a, co-diamines. It was shown that the reaction proceeds through various intermediates and it can be illustrated by the following Eqs. (1)—(3). 

Pailer and Fenzl lx) replaced the trialkylboranes in this pyrolysis reaction by organoboron dihalides, RBX2, and obtained the 1,3,2-dia-zaboracycloalkane system under evolution of hydrogen halide. 

In addition to pyrolysis, transamination, and dehydrohalogenation with tertiary amines several other reactions have been described which yield access to the 1,3,2-diazaboracycloalkane system. For example, Abel and Bush 19> reported the ready replacement of silicon by boron in certain heterocyclic systems as illustrated in Eq. (6). It seems quite likely that this procedure can be developed into a general synthesis. On the other hand, the interaction of trialkylboranes with bis(l,3-diphenylimidazolid-... 

Pyrolysis of trialkylboranes having eight or more carbons in the main alkyl chain gives bicyclic, as well as monocyclic, products (64). Tri- -octyl-borane loses two moles of hydrogen, giving 8-borahydrindane (LI II) in good yields the octene isomers have predominantly central C=C bonds. 

Higher trialkylboranes readily pyrolyze to form 9-boradecalins and their Cl-alkyl derivatives. Tri-n-nonylborane gives 9-boradecalin (LIV) in 80% yield under suitable conditions (temperatures of 250-300° C and short reaction times). Monocyclic boranes form initially these convert to bicyclic compounds (LIV) under progressive pyrolysis. 

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