Aminoborohydrides. 13. facile reduction of N-alkyl lactams with 9- borabicyclo[3.3.1]nonane (9-BBN) and lithium aminoborohydrides (LAB) reagents

Two methods to reduce N-alkyl lactams to the corresponding cyclic amines using 9borabicyclo[3.3.1]nonane (9-BBN) and lithium aminoborohydride (LAB) reagents are reported. The lactam reductions required 2.2 molar equivalents of 9-BBN or 1.5 molar equivalents of LAB reagent and were complete within two hours in refluxing THF (65 °C). Reductions with these reagents are chemoselective and complementary in nature. A lactam can be reduced in the presence of an ester with 9BBN. At lowered temperature, an ester can be reduced in the presence of lactam with LAB reagents. At elevated temperature, LAB reagents act as powerful reducing agents, and reduce both lactam and ester functional groups in a difunctional molecule. The reaction products were easily isolated in good to excellent yields after simple work-ups.