Studies On Reductive Oxy-nazarov Cyclization

The classic Nazarov electrocyclic reaction is an effective method to buildfive-membered ring skeleton with multiple functional groups. However, limitations stillexist in practical applications of this reaction in organic synthesis due to the lack ofregio-and stereoselective control.A new oxy-Nazarov reaction was developed in our research group previously,which features:(1) wide substrate scope and implementation oxy-functional groupstereospecifically and (2) predictable asymmetric control with C-2chiral diol auxiliary(Scheme1).The first part of this thesis is on the reinvestigation of the experimental studies onthe1,3-dioxolan-2-one derivatives reported in1984by Ramage and co-workers (J.Chem. Soc., Perkin Trans. I1984,15311537). The preparation and purification ofconfigurational isomers (2-24E) and（2-24Z) were achieved and subjected to thereduction conditions with Dibal-H in toluene at78C, respectively. We have concludedon the basis of our experimental results that the reported formation of cyclopentenoneproduct (2-25） is the result of the oxy-Nazarov cyclization of the EE-isomer(2-24E)(Scheme2). The second part of the thesis described the design and synthesis of benzo[b]-1,4-dioxin-2-one derivative（2-31）as a novel type of oxy-Nazarov cyclization substrate.5-Hydroxy-cyclopentenone derivative （2-34）was characterized as the sole regio-andstereospecific cyclization product under the standard reduction conditions withDibal-H (Scheme3).