Synthesis of methoxyisopropyl (MIP)-protected (R)-mandelonitrile and derivatives in a flow reactor

Cyanohydrins are synthetically versatile chiral building blocks in organic synthesis. They can be conveniently synthesized in enantiomerically pure form via chemoenzymatic hydrogen cyanide addition onto the corresponding aldehyde using hydroxynitrile lyase. Recently, we reported that such transformations can be efficiently carried out in a continuous flow manner using microreactors. Since racemization of enantiopure cyanohydrins occurs readily under slightly basic conditions, they should be protected before the follow-up reactions, preferably under acidic conditions. In this contribution, we demonstrate that the methoxyisopropyl protection of mandelonitrile can be conveniently optimized in an automated microscale continuous flow system and subsequently scaled up under the same conditions by applying a larger flow reactor.