6-hydroxy-3-pyridazinecarboxylic acid ethyl ester   、                                                                                      
3,4-epoxy-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran-6-carbonitrile                                                                                                                                                              在
                                                                                                                                                                                 
吡啶                                                                                                                                  作用下,
                                                                                                                以
                                                                                         
乙醇                                                                                  为溶剂,
                                                                                                                                                    反应 2.0h,
                                                                                                                以65%的产率得到1-((3S,4R)-6-Cyano-3-hydroxy-2,2-dimethyl-chroman-4-yl)-6-oxo-1,6-dihydro-pyridazine-3-carboxylic acid ethyl ester