Enantioselective synthesis of diversely substituted quaternary 1,4-benzodiazepin-2-ones and 1,4-benzodiazepine-2,5-diones

Benzodiazepines are privileged scaffolds in medicinal chemistry, but enantiopure examples containing quaternary stereogenic centers are extremely rare. We demonstrate that installation of the di(p-anisyl) methyl ( DAM) group at N1 of 1,4- benzodiazepin- 2- ones and 1,4- benzodiazepine- 2,5- diones derived from enantiopure proteinogenic amino acids allows retentive replacement of the C3- proton via a deprotonation/ trapping protocol. A wide variety of carbon and nitrogen electrophiles function well in this reaction, providing the corresponding quaternary benzodiazepines with excellent enantioselectivity. Deprotonation/ trapping experiments on a pair of diastereomeric 1,4- benzodiazepine- 2,5- diones provide evidence for a key role of conformational chirality in these enantioselective reactions. Acidic removal of the DAM group is fast and high- yielding and can be performed selectively in the presence of a N- Boc indole. Thus the synthesis of quaternary benzodiazepines with diverse N1 functionality can now be accomplished.