108593-89-1Relevant academic research and scientific papers
Flash Vacuum Pyrolysis of o-Alkylaryl- and Arylalkylchloroboranes. - Synthesis of Benzoannulated Boracycloalkenes
Schacht, Wolfgang,Kaufmann, Dieter
, p. 1331 - 1338 (2007/10/02)
The dichloroorganylboranes chosen as pyrolytic starting materials were synthesized upon treatment of the corresponding triorganylboroxines and aryltrimethylsilanes (giving 3, 4) or the tetraorganylstannanes (giving 9-12, 17-20) with boron trichloride.At 700 deg C the flash vacuum pyrolysis of the dichloro(2-ethylphenyl)boranes 10 and 4 led to 1-boraindanes 21 and 22 selectively.The dichloro-2-tolylborane (9), the B-dimethylamino derivative, and mesitylboranes like 3 were completely stable upon pyrolysis.Pyrolyzing the isopropylphenylborane 12 1,5-elimination exclusively took place yielding 26, while pyrolysis of propylphenylborane 11 led to a mixture of boraindane 29 and boratetraline 30.To exclude such competitive reactions, some arylalkyldichloroboranes were pyrolyzed.At 750 deg C dichloro(2-methylbenzyl)borane (18) exclusively yielded oligomeric 2-chloro-2-boraindane (31).At 950 deg C even the pyrolysis of benzyldichloroborane (17) succeeded in a 1,4-elimination reaction yielding the eight-membered 2H-benzoborete dimer 34.The inversion barrier of 34 is ΔG(excit.)228 = 10.3 kcal mol-1, determined by NMR spectroscopy.The pyrolysis of the next-higher homologous dichloroorganylborane 19 yielded a boraindane 21 and a noncyclic diorganylborane 38 by a dehydroboration/hydroboration pathway.Both reaction types also took place when pyrolyzing dichloroborane (20): cyclization under formation of a five-membered ring system 39, formed upon attack of an aromatic C-H bond exclusively, and formation of an open-chain chlorodiorganylborane 40.
