Catalyzed hydroboration of allyl sulfonamides

The hydroboration of allyl sulfonamides (4-H3CC6H4SO2NRCH2CHCH2: R=H, 1; Ph, 2; Bz, 3) with catecholborane (HBcat) using different rhodium catalysts has been examined using multinuclear NMR spectroscopy. Reactions give complex product distributions, regardless of the choice of catalyst, arising from a competing isomerization reaction. This isomerization reaction can be used with N-substituted allyl sulfonamides 2 and 3 to give the corresponding enamines (4-H3CC6H4SO2CHCH2CH3), which in turn react with HBcat to give regioselective formation of one isomer (4-H3CC6H4SO2NRCH2CH2(Bcat)CH3).