Stereocontrolled [4+1] Annulation Of ?-Hydroxycyclobutenones:Synthesis Of Polysubstituted Cyclopentenones

According to the seminal studies from Moore and Liebeskind about these various reactions of a-hydroxycyclobutenones,its unique chemical propreties were revealed that a-hydroxycyclobutenones could be readily transformed into an enol-ketene intermediate at high torquoselectivity through a four-electron electrocyclic ring-opening process under thermal conditions.Moreover,a-hydroxycyclobutenones have been confirmed as important C4 synthons,which can be extensively utilized in varieties interesting reactions and signficant strategies for the synthesis of natural products.Because of the broad diversity of chemical modifications available for the enone structural motif,the cyclopentenone unit can serve as a very powerful synthon for the synthesis of a variety of bioactive target molecules.Notably,the[4+1]annulation represents a versatile strategy to five-membered ring molecules and has become an attractive topic in recent decades.We reported the first example of an intermolecular reaction after the ring opening of a-hydroxycyclobutenone,a four-electron electrocyclic ring-opening/intermolecular[4+2]cycloaddition of a-hydroxycyclobutenones and imines.The development of new strategies and chemical reactions continues to be a major focus of research efforts in the modern synthetic organic community.In this paper,a-hydroxycyclobutenones have been proven as suitble diene precursors in[4+1]annulations with trimethylsilyldiazomethane?TMSD?for the first time.Due to the contributionof 1,3 allylic strain in the disfavored transition state,this novel developed[4+1]process affords a concise andstereocontrolled approach to polysubstituted cyclopentenones.Noteworthy,it is discoveredthat this intermolecular[4+1]annulation is even more favorable than the intramolecular four-electronelectrocyclic ring-opening/6?-electrocyclization process with a-hydroxycyclobutenones bearing aryl or alkynyl groups as the C₄ substituent.