No abstract

Catalytic asymmetric hydrogenation of N-Boc-protected pyrroles proceeded with high enantioselectivity by using a ruthenium catalyst modified with a trans-chelating chiral bisphosphine PhTRAP. The ruthenium catalyst prepared from Ru(eta3-methallyl)2(cod) and (S,S)-(R,R)-PhTRAP in the presence of triethylamine was the most enantioselective for the asymmetric hydrogenation of methyl pyrrole-2-carboxylate, giving the desired (S)-proline derivative with 79% ee in 92% yield. Moreover, 2,3,5-trisubstituted pyrroles bearing a large substituent at the 5-position were hydrogenated with 93-99.7% ee. The asymmetric reduction of 4,5-dimethylpyrrole-2-carboxylate gave only all-cis isomer and created three chiral centers with high degree of stereocontrol in a single process. This is the first highly enantioselective reduction of pyrroles.

Benzyl protection of phenols under neutral conditions was achieved by using a Pd(eta3-C3H5)Cp-DPEphos catalyst. The palladium catalyst efficiently converted aryl benzyl carbonates into benzyl-protected phenols through the decarboxylative etherification. Alternatively, the nucleophilic substitution of benzyl methyl carbonates with phenols proceeded in the presence of the catalyst, yielding aryl benzyl ethers.

Approval of avibactam by the FDA has led to the recognition of 1,6-diazabicyclo[3.2.1]­octane (DBO) derivatives as attractive compounds for β-lactamase inhibition. We achieved a concise and collective synthesis of 2-thio-substituted DBO derivatives. The synthesis involves diastereoselective photo-induced Barton decarboxylative thiolation, which can be applied to large-scale synthesis. The DBO analogues exhibited strong inhibitory activities against serine β-lactamases and acceptable solution stabilities for clinical development.