The efficient photochemical synthesis of 5-alkoxy- and 5-acetoxy-3-oxo-2-azabicyclo[2.2.0]hex-5-enes (2a–e and f,g), and a new rearrangement reaction of the former compounds (2a–e) to 6-alkoxy-2-pyridones (3a–e), are reported.
Photochemistry of 2-pyridonemixtures can be selective and thereby lead to useful quantities of [4 + 4] cycloaddition cross products. The selectiveintermolecular reaction described here employs an excess of 4-methoxy-2-pyridone (6), which does not photodimerize but will undergo [4 + 4] cycloaddition with 2-pyridones without a 4-methoxy group such as N-butyl-2-pyridone 12. Isolated yields of the trans
2-Azabicyclo[2.2.0]hexane-3,5-dione is synthesized via photopyridone formation from 4-(t-butyldimethylsilyloxy)- or 4-alkoxy-2-pyridone followed by mild acid hydrolysis and reacts with a variety of alcohols or thiols to give 4-alkoxycarbonyl- or 4-alkylthiocarbonyl-methylazetidin-2-ones.