Use of Suzuki cross-coupling as a route to 2-phenoxy-6-iminopyridines and chiral 2-phenoxy-6-(methanamino)pyridines
作者:Christopher J. Davies、Andrew Gregory、Phillip Griffith、Tom Perkins、Kuldip Singh、Gregory A. Solan
DOI:10.1016/j.tet.2008.08.019
日期:2008.10
The anisyl boronic acids, 2-OMe-3-R-2-5-R-1-C6H2B(OH)(2) (R-1=R-2=H (a); R-1=H, R-2=Ph (b); R-1=Me, R-2=H (c); R-1=Cl, R-2=H (d); R-1=t-Bu, R-2=H (e)), have been employed in Suzuki cross-coupling reactions with either 2-bromo-6-formylpyridine (1) or 2-bromo-6-acetylpyridine (11) generating, following a facile deprotection step, the 2-phenoxy-6-carbonylpyridines, 2-(2'-OH-3'-R-2-5'-R-1-C6H2)-6-(CH=O)C5H3N (R-1=R-2=H (1a); R-1=Me, R-2=H (1c); R-1=Cl, R-2=H (1d); R-1=t-Bu, R-2=H (1e)) and 2-(2'-OH-3'-R-2-5'-R-1-C6H2)-6-(CMe=O)C5H3N (R-1=R-2=H (2a); R-1=H, R-2=Ph (2b)). Condensation reactions of 1 and 2 with 2,6-diisopropylaniline proceed smoothly to give the 2-phenoxy-6-iminopyridines, 2-(2'-OH-3'-R-2-5'-R-1-C6H2)-6-CH=N(2,6-i-Pr2C6H3)}C5H3N (R-1=R-2=H (3a); R-1=Me, R-2=H (3c); R-1=Cl, R-2=H (3d); R-1=t-Bu, R-2=H (3e)) and 2-(2'-OH-3'-R-2-5'-R-2-C6H2)-6-CMe=N(2,6-i-Pr2C6H3)}C5H3N (R-1=H, R-2=Ph (4a), R-1=H, R-2=Ph (4b)). Reduction of the imino unit (and concomitant C-C bond formation) in 3 can be achieved by treatment with trimethylaluminium or methyllithium which, following hydrolysis, furnishes the racemic chiral 2-phenoxy-6-(methanamino)pyridines, 2-(2'-OH-3'-R-2-5'-R-1-C6H2)-6-CHMe-NH(2,6-i-Pr2C6H3)}C5H3N R-1=R-2=H (5a); R-1=Me, R-2=H (5c); R-1=Cl, R-2=H (5d); R-1=t-Bu, R-2=H (5e)). This work represents a straightforward and rapid synthetic route to libraries of sterically and electronically variable phenoxy-substituted imino- and methanamino-pyridines, which are expected to act as useful ligands or proligands for late and early transition metal-mediated alkene polymerisation catalysis. (C) 2008 Elsevier Ltd. All rights reserved.