Catalytic Amide Reductions under Hydrosilylation Conditions

Abstract: This thesis covers the development of catalytic methodologies for the mild and chemoselective reductions of amides. The first part of the thesis describes the use of a Fe(II)/NHC catalyst for the deoxygenation of aromatic tertiary amides to corresponding amines. The protocol is characterized by low catalyst loading, mild reaction conditions and the use of air and moisture stable polymethylhydrosilaxane (PMHS) as the hydride source.The second part concerns the development of a protocol for the room temperature deoxygenation of a wide range of tertiary amides to amines using catalytic amounts of Et2Zn and LiCl together with PMHS. The system displayed high levels of chemoselectivity tolerating various reducible groups such as nitro, nitrile, and olefin functionalities, and was shown to be applicable for the reduction of aromatic, heteroaromatic and aliphatic tertiary amides.The attempts to expand the scope of the Fe-based protocol to accommodate benzylic tertiary amides led to the development of a transition metal-free catalytic system based on KOtBu for the formation of enamines. The final products constitute an important class of precursors for a wide range of valuable compounds in organic chemistry. Moreover, avoiding the use of transition metals in the protocol allowed the desired products to be obtained without the hazardous metal contaminants.The last chapter of the thesis describes the Mo(CO)6-catalyzed hydrosilylation of amides. The Mo-based catalyst was proven to mediate the deoxygenation of α,β-unsaturated tertiary and secondary amides to the corresponding allylamines without reduction of the olefinic bonds. Further development of the catalytic system revealed an unprecedented chemoselectivity in the hydrosilylation of aromatic and certain aliphatic tertiary amides in the presence of a variety of reducible groups along with aldehydes and imines that were tolerated for the first time. Moreover, it was possible to control the reaction outcome by variation of the reaction temperature to obtain either amines or aldehydes as the major products. The synthetic utility of the developed Mo(CO)6-catalyzed protocols was further demonstrated in the synthesis of the pharmaceuticals Naftifine and Donepezil.