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Chiral 2,3‐Dihydro‐1 H ‐1,3,2‐diazaboroles
Author(s) -
Weber Lothar,
Rausch Andreas,
Wartig Henning B.,
Stammler HansGeorg,
Neumann Beate
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200209)2002:9<2438::aid-ejic2438>3.0.co;2-w
Subject(s) - chemistry , methyllithium , aminolysis , medicinal chemistry , proton nmr , stereochemistry , organic chemistry , catalysis
A series of differently substituted chiral 2,3‐dihydro‐1 H ‐1,3,2‐diazaboroles has been prepared by various methods. 2Bromo‐1‐ tert ‐butyl‐3‐[( S )‐1‐phenylethyl]‐2,3‐dihydro‐1 H 1,3,2‐diazaborole ( 3a ), 2‐bromo‐1,3‐di[( S )‐1‐phenylethyl]‐2,3‐dihydro‐1 H ‐1,3,2‐diazaborole ( 3b ) and 2‐bromo‐1,3di[( S )‐1‐cyclohexylethyl]‐2,3‐dihydro‐1 H ‐1,3,2‐diazaborole ( 3c ) were formed from the reaction of the corresponding 1,4‐diazabutadienes and boron tribromide and the subsequent reduction of the resulting borolium salts [R 1 N a = CH−CH=N b (R 2 )BBr 2 ]Br( N a − B ) [ 2a : R 1 = t Bu, R 2 = CH(Me)Ph; 2b : R 1 = R 2 = CH(Me)Ph; 2c : R 1 = R 2 = CH(Me)( c C 6 H 11 )] with sodium amalgam. Treatment of ( S )‐ 3a with LiAlH 4 or methyllithium afforded 1‐ tert ‐butyl‐2‐hydro‐3‐[( S )‐1‐phenylethyl]‐2,3‐dihydro‐1 H ‐1,3,2‐diazaborole [( S )‐ 6 ] and 1‐ tert ‐butyl‐2‐methyl‐3[( S )‐1‐phenylethyl]‐2,3‐dihydro‐1 H ‐1,3,2‐diazaborole [( 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‐1 H ‐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‐1 H ‐1,3,2‐diazaborole derivatives ( S,S )‐ 11 and ( S,S )‐ 12 , respectively. The 2‐trimethylstannyl‐2,3‐dihydro‐1 H ‐1,3,2‐diazaboroles ( S,S )‐ 10 and ( S,S )‐ 14 were accessible from 3b or 3c and trimethylstannyllithium. The transformation of achiral 2bromo‐1,3‐di‐ tert ‐butyl‐2,3‐dihydro‐1 H ‐1,3,2‐diazaborole into the chiral ( S )‐2‐[1‐phenylethylamino]‐ and ( S )‐2‐[1‐cyclohexyl‐ethylamino] 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 1 H, 11 B, 13 C, and 119 Sn 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. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)