The in situ rhodium-catalyzed addition of catecholborane (HBcat, cat = 1,2-O2C6H4) and pinacolborane (HBpin, pin = 1,2-O2C2Me4) to allylamine, allylimine, 2- and 4-vinylpyridines, and a thienyl imine has been examined using multinuclear NMR spectroscopy. Although reactions of allylamine (H2NCH2CH=CH2) and HBcat gave complex product distributions arising from competing dehydrogenative borylation pathways, addition of HBpin to allylamine using a rhodium catalyst afforded only products arising from hydroboration (RN(Bpin)CH2CH2CH2Bpin, where R = H, Bpin) and hydrogenation (RN(Bpin)CH2CH2CH3). Hydroboration of allylimines (RHC=NCH2CH=CH2, R = Ar) with HBcat occurs initially at the more reactive imine functionality to give unsaturated borylamines (RCH2N(Bcat)CH2CH=CH2). Further reaction with HBcat gives varying amounts of hydroboration products RCH2N(Bcat)CH2CH2CH2Bcat and RCH2N(Bcat)CH2CH(Bcat)CH3 as well as the diboration product RCH2N(Bcat)CH2CH2CH(Bcat)2, depending on the choice of catalyst. Reactions with related unsaturated pyridine derivatives are complicated by extensive degradation, which can be avoided by coordination of the pyridine nitrogen to a Lewis acid. The first examples of metal-catalyzed hydroboration of imines using HBpin are also reported.Key words: catalysis, hydroboration, boronate esters, dehydrogenative borylation, allylimines.
The in situ rhodium-catalyzed addition of catecholborane (HBcat, cat = 1,2-O 2 C 6 H 4) and pinacolborane (HBpin, pin = 1,2-O 2 C 2 Me 4) to allylamine, allylimine, 2-and 4-vinylpyridines, and a thienyl imine has been examined using multinuclear NMR spectroscopy. Although reactions of allylamine (H 2 NCH 2 CH=CH 2) and HBcat gave complex product distributions arising from competing dehydrogenative borylation pathways, addition of HBpin to allylamine using a rhodium catalyst afforded only products arising from hydroboration (RN(Bpin)CH 2 CH 2 CH 2 Bpin, where R = H, Bpin) and hydrogenation (RN(Bpin)CH 2 CH 2 CH 3). Hydroboration of allylimines (RHC=NCH 2 CH=CH 2 , R = Ar) with HBcat occurs initially at the more reactive imine functionality to give unsaturated borylamines (RCH 2 N(Bcat)CH 2 CH=CH 2). Further reaction with HBcat gives varying amounts of hydroboration products RCH 2 N(Bcat)CH 2 CH 2 CH 2 Bcat and RCH 2 N(Bcat)CH 2 CH(Bcat)CH 3 as well as the diboration product RCH 2 N(Bcat)CH 2 CH 2 CH(Bcat) 2 , depending on the choice of catalyst. Reactions with related unsaturated pyridine derivatives are complicated by extensive degradation, which can be avoided by coordination of the pyridine nitrogen to a Lewis acid. The first examples of metal-catalyzed hydroboration of imines using HBpin are also reported.
2002 organo-boron compounds organo-boron compounds S 0040 28 -209 Rhodium-Catalyzed Hydroborations of Allylamine and Allylimines. -Different products are obtained depending on the nature and ratio of educts. Hydroboration of vinylpyridines is also studied. -(VOGELS, CHRISTOPHER M.; O'CONNOR, PAUL E.; PHILLIPS, TREVOR E.; WAT-SON, KEITH J.; SHAVER, MICHAEL P.; HAYES, PAUL G.; WESTCOTT, STEPHEN A.; Can.
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