Synthesis of 2,3-Dihydrobenzofurans by Mn(OAc)<sub>3</sub>-Based Oxidative Cycloaddition of 2-Cyclohexenones with Alkenes. Synthesis of (±)-Conocarpan
                                
                                    
                                        作者:Barry B. Snider、Luning Han、Chaoyu Xie                                    
                                    
                                        DOI:10.1021/jo9708506
                                    
                                    
                                        日期:1997.10.1
                                    
                                    Oxidative cycloaddition of a 2-cyclohexenone or alpha-tetralone and an alkene with dried Mn(OAc)(3) in benzene at 80-140 degrees C provides a general route to dihydrobenzofurans 15 and dihydronaphthofurans 17. Although the yields are modest, this one-pot reaction provides simple access to these compounds, which have previously been prepared by multistep routes. Oxidative cycloaddition of 2-cyclohexenones with beta-methylstyrenes provides a new route to benzofuranoid neolignans, which was applied to the synthesis of conocarpan (22). The formation of 2-acetoxyhexanedioic acids 27 and 47 from acetoxylation of 2-cyclohexenones in HOAc, but not in benzene, opens up a new class of Mn(OAc)(3) reactions and explains Watt and Demir's discovery that much higher yields of alpha'-acetoxy enones are obtained in benzene than in HOAc.