Domino Reactions Initiated by Reduction Reaction

Recently, extensive efforts have been made in the development of domino conjugate reduction/inter and intramolecular aldol reaction catalyzed by various metal complexes based on rhodium, iridium, cobalt, indium, nickel, and copper [22]. In 1999, Morken and Taylor [23] reported a rhodium-catalyzed conjugative reductive/aldol reaction between aldehyde and acrylate using QjMeSiH as reducing agent with a maximum diastereoselectivity of 23 1. 

2 Domino Reactions initiated by Oxidation or Reduction Reaction I 303 

A general mechanism of domino conjugate reduction/aldol reactions applying the in situ formation of metal hydrides 71 from metal complex 70 by reduction with 

P-Lactams have been of great synthetic interest because of their use as antibiotic agents, protease inhibitors, and chlolesterol absorption inhibitors [34]. Morken et al. [35] disclosed an efficient iridium-catalyzed diastereoselective synthesis of trans-P-lactams 83 from acrylates 82 and imines 81 through a reductive Man-nich addition/cyclization (Table 9.1). The yields ranged from 58 to 80% and the diastereoselectivity exceeded 20 1. 

Pyrrolizidinones have been found to be potent anti-inflammatory and antidepressant drugs [36]. Recently, Sukhorukov et al. developed a novel domino reductive ring-opening/double cychzation method for the synthesis of pyrrolizidinone 89, which is considered as a highly potent second-generation phospho diesterase IVb inhibitor. 

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