Tricyclic spiro- N, O-acetals have been assembled in a single step by cycloaddition of hydroxymethyl-substituted dienes to iminium ion activated dienophiles that were generated by acidolysis of α,β-unsaturated- N-carboalkoxy- N, O-acetals or β-methoxymethyl- N-carboalkoxy-enamines. The cycloaddition was conducted using Sc(OTf) 3 as a mild Lewis acid affording the ENDO adducts in moderate yields.
                                    三环螺-N,O-
缩醛通过将羟甲基取代的二烯环加成到
亚胺离子活化的亲二烯体,由α,β-不饱和-N-碳烷氧基-N,O-
缩醛或β的酸解产生-甲氧基甲基-N-碳烷氧基-烯胺。使用Sc(OTf) 3 作为温和的
路易斯酸进行环加成,以中等产率提供ENDO加合物。