INTRAMOLECULAR 1,3-DIPOLAR CYCLOADDITION OF STABILIZED AZOMETHINE YLIDES TO UNACTIVATED DIPOLAROPHILES

The scope and limitations of the intramolecular 1,3-dipolar cycloaddition of doubly-stabilized azomethine ylides to unactivated olefinic, acetylenic, and aromatic dipolarophiles is reported. The azomethine ylides studied were generated by flash vacuum pyrolysis of their corresponding aziridines and were found to add stereospecifically in good to excellent yields to a variety of unactivated dipolarophiles. Generation of the diazabicyclo[3.3.0]octane (e.g., 15a,b), diazabicyclo[4.3.0]nonane (e.g., 4,13), and diazabicyclo[5.3.0]decane (e.g., 15c) ring systems are possible using this technology. In addition, the first examples of cycloaddition of a stabilized azomethine ylide to benzene dipolarophiles are reported. Cycloadditions of this type generate highly functionalized triciclic systems with complete relative stereocontrol at the newly formed stereocenters (e.g., 24-26). Finally, it has been shown that cycloadducts 31 and 32 are in equilibrium, presumably by way of the intermediate azomethine ylide 33, under conditions of flash vacuum pyrolysis.