PUB - Publikationen an der Universität Bielefeld

A series of differently substituted chiral 2,3-dihydro-1H-1,3,2-diazaboroles has been prepared by various methods. 2-Bromo-1-tert-butyl-3-[(S)-1-phenylethyl]-2,3-dihydro-1H-1,3,2-diazabor ole (3a), 2-bromo-1,3-di[(S)-1-phenylethyl]2,3-dihydro-1H-1,3,2-diazaborole (3b) and 2-bromo-1,3di[(S)-1-cyclohexylethyll-2,3-dihydro-1H-1,3,2-diazaborole (3c) were formed from the reaction of the corresponding 1,4diazabutadienes and boron tribromide and the subsequent reduction of the resulting borolium salts [(RNa)-N-1 = CH-CH = N-b(R-2)BBr2]Br(N-a-B) [2a: R-1 = tBu, R-2 = CH(Me)Ph; 2b: R-1 = R-2 = CH(Me)Ph; 2c: R-1 = R-2 = CH(Me)(CC6H11)] with sodium amalgam. Treatment of (S)-3a with LiAlH4 or methyllithium afforded 1-tert-butyl-2-hydro-3-[(S)-1-phenylethyll-2,3-dihydro-1H-1,3,2-diazabor ole [(S)-6] and 1-tert-butyl-2-methyl-3[(S)-1-phenylethyl]-2,3-dihydro-1H-1,3,2-didzabor ole [(S)-7], respectively. Aminolysis of the BBr bond of (S)-3a by tert-butylamine or (S)-1-phenylethylamine gave the corresponding 2-tert-butylamino- and 2-(1-phenylethylamino]-2,3-dihydro-1H-1,3,2-diazaboroles (S)-8 and (S,S)-9, respectively. Similarly, (S,S)-3b and (S,S)-3c were reacted with tert-butylamine to furnish the 2-tert-butylamino-2,3-dihydro-1H-1,3,2-diazaborole derivatives (S,S)-11 and (S,S)-12, respectively. The 2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaboroles (S,S)-10 and (S,S)-14 were accessible from 3b or 3c and trimethylstannyllithium. The transformation of achiral 2-bromo-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole into the chiral (S)-2-[1-phenylethylamino]- and (S)-2-[1-cyclohexyl-ethylaminol derivatives (S)-15 and (S)-16 was effected by aminolysis with enantiomerically pure (S)-1-phenylethylamine or (S)-1-cyclohexylethylamine. The novel compounds were characterized by H-1, B-11, C-13, and Sn-119 NMR spectroscopy as well as mass spectrometry and determination of the optical rotation. The molecular structure of compound 3c was confirmed by X-ray structural analysis.