Highly Enantioselective Bromocyclization of Allylic Amides with a P/P=O Double-Site Lewis Base Catalyst.

The enantioselective bromocyclization of allylic amides catalyzed by phosphorus-containing Lewis bases was examined in detail. A series of control experiments and NMR studies showed that a partially oxidized bis-phosphine generated in situ serves as the actual enantioselective catalyst. The reaction mechanism involves distinct roles of two Lewis basic sites, P and P=O, with P Br serving as a fine-tuning element for substrate fixation in the chiral environment, and P OBr as the Br transfer agent to the olefin.

Enantioselective bromocyclization of allylic amides catalyzed by BINAP derivatives.

A highly enantioselective bromocyclization of allylic amides with N-bromosuccinimide (NBS) was developed with DTBM-BINAP as a catalyst, affording chiral oxazolines with a tetrasubstituted carbon center in high yield with up to 99% ee. By utilizing the bromo substituent as a handle, the obtained compounds were converted to synthetically useful chiral building blocks.