Intramolecular ipso-Cyclization of N-Arylpropiolamides: A Novel and Straightforward Synthetic Approach for Azaspiro[4.5]decatrien-2-ones

Background: Spiro[4.5]decenones are privileged structural motifs occurring in various biologically active natural and unnatural compounds. Moreover, they are very important intermediates in organic synthesis. Therefore, the development of novel one-pot protocols for the synthesis of these synthetically challenging spirocyclic compounds that benefit from simple, inexpensive, and readily available starting materials continues to be a target of intense interest. In recent years, tremendous efforts have been made toward the construction of titled compounds form cheap and readily accessible N-arylpropiolamide derivatives through intramolecular ipso-cyclization strategy. Objective/Methodology: This review highlights recent advances in this explosive growing research area from the year 2005 to 2017. Conclusion: The review is divided into three major sections. The first section focuses exclusively on ipso-halocyclization approaches. The second section will discuss oxidative radical ipso-cyclizations. The third will cover catalytic ipso-cyclizations. Mechanistic aspects of the reactions are considered and discussed in detail.