Mimicking a naturally occurring reducing agent

The Hantzsch ester, 3,5-bis(ethoxycarbonyl)l,4-dihydro-2,6-dimethylpyr-idine, 3, can be made to mimic the behaviour of coenzyme NADPH by the addition of silica gel which acts as an acid catalyst [117]. 

This reducing system can be used for a wide range of selective reductions of imines [118] (e.g. equations 4.24, 4.25) and olefins [119]. 

---