An Efficient Synthesis of Optically Active trans ‐(3 R ,4 R )‐3‐Acetoxy‐4‐aryl‐1‐(chrysen‐6‐yl)azetidin‐2‐ones Using (+)‐Car‐3‐ene as a Chiral Auxiliary

An efficient enantioselective synthesis of 3‐acetoxy trans ‐ β ‐lactams 7a and 7b via [2+2] cycloaddition reactions of imines 4a and 4b , derived from a polycyclic aromatic amine and bicyclic chiral acid obtained from (+)‐car‐3‐ene, is described. The cycloaddition was found to be highly enantioselective, producing only trans‐ (3 R ,4 R )‐ N ‐azetidin‐2‐one in very good yields. This is the first report of the synthesis of enantiomerically pure trans ‐ β ‐lactams 7a and 7b with a polycyclic aromatic substituent at N(1) of the azetidin ring.