Iodocyclization-Based Synthesis of Spiro Heterocycles

Significance

Reported is the spirocyclization of ortho-alkoxy N- and O-propargyl anilines and phenols. This process is mediated by a combination of NIS and BF₃˙OEt₂, both of which are necessary for satisfactory yields. The reaction appears to tolerate a reasonable range of nitrogen substituents; however, it is not so tolerant of alkynyl analogues, since the reaction fails when R^¹ = n- or t-Bu. When aromatic propargyl ethers are used the products undergo spontaneous ­Diels-Alder reactions to give very interesting complex products. These were further elaborated through Stille and Sonogashira cross-coupling chemistry.