Amine-directed hydroboration: scope and limitations.
Iodine activation induces intramolecular hydroboration of homoallylic and bis-homoallylic amine boranes with good to excellent control of regiochemistry compared to control experiments using excess THF*BH 3. Deuterium labeling and other evidence confirm that the iodine-induced hydroboration reaction of homoallylic amine boranes occurs via an intramolecular mechanism equivalent to the classical 4-center process and without competing retro-hydroboration. Longer carbon chain tethers result in lower regioselectivity, whereas the shorter tether in allylic amines results in a switch to dominant intermolecular hydroboration. Regioselectivity in THF*BH 3 control experiments is higher for the allylic amine boranes compared to the iodine activation experiments, whereas the reverse is true for homoallylic amine borane activation.
Scheideman
Matthew
M
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Wang
Guoqiang
G
Vedejs
Edwin
E
D000588:Amines / Q000737:chemistry*; D001880:Boranes / Q000737:chemistry*; D001895:Boron / Q000737:chemistry*; D003903:Deuterium / Q000737:chemistry; D005663:Furans / Q000737:chemistry; D007455:Iodine / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D000588:Amines; D001880:Boranes; D005663:Furans; D014867:Water; C018674:tetrahydrofuran; D007455:Iodine; D003903:Deuterium; D001895:Boron