[4+2] Cycloaddition of 1,3-dienes  to glycolaldehyde derivatives, leading to 5,6-dihydro-2H-pyrans, was effected by high pressure  (10 kbar) in the presence of Eu(fod)3 (2%).  Enantioselective version of the reaction was also studied.
                                    在 Eu(fod)3 (2%) 存在下,通过高压(10 千巴)将 1,3 二烯与
乙醛衍
生物进行 [4+2] 环加成反应,生成 5,6 二氢-
2H-吡喃。  还研究了该反应的对映体选择性。