AZETIDINES AND BISAZETIDINES - THEIR SYNTHESIS AND USE AS THE KEY INTERMEDIATES TO ENANTIOMERICALLY PURE DIAMINES, AMINO-ALCOHOLS, AND POLYAMINES

Highly selective reductions of beta-lactams (1, 5), direct-tandem bis-beta-lactams (6), and tandem bis-beta-lactams (7) to the corresponding azetidines (13, 14) and bisazetidines (11, 12) are successfully performed by using diisobutylaluminum hydride (DIBAL-H), monochlorohydroalane (AlH2Cl) and dichloroalane (AlHCl2) as specific reducing agents: Enantiomerically pure azetidines and bisazetidines are readily synthesized without loss of enantiomeric purity. Possible mechanisms that can accommodate the unique selectivity realized by hydroalanes are discussed. Hydrogenolysis of 2-arylazetidines and 2,2'-diarylbisazetidines on palladium catalyst or Raney-Ni gives the corresponding diamines, amino alcohols, polyamino alcohols, and polyamino ethers in excellent yields, which may serve as useful chiral chelating agents as well as chiral building blocks for organic synthesis and for chiral macrocycles.