Stereoselective α,α′-Annelation Reactions of 1,3-Dioxan-5-ones

Pyrrolidine enamines derived from three 1,3-dioxan-5-ones undergo α,α′-annelation reactions with methyl α-(bromomethyl)acrylate to produce bridged 2,4-dioxabicyclo[3.3.1]nonane ring systems with complete stereocontrol. Stereochemical outcomes have been rationalized based on steric and stereoelectronic interactions in intermediate boat-like conformations of the 1,3-dioxane ring and subsequent kinetic protonation to set an axial ester group on the cyclohexanone ring. Base-mediated ester epimerization provides the stereochemical array found in the highly oxygenated cyclohexane ring of phyllaemblic acid and glochicoccins B and D.

由三种1,3-二氧杂环戊-5-酮衍生的吡咯烷亚胺与甲基α-（溴甲基）丙烯酸甲酯发生α,α′-联烯反应，生成具有完全立体控制的桥连2,4-二氧杂双环[3.3.1]壬烷环系统。基于1,3-二氧杂环的中间船形构象中的立体和立体电子相互作用，以及随后的动力学质子化，在环己酮环上设置轴向酯基，对立体化学结果进行了合理化解释。基于碱催化的酯赤式异构化，提供了在叶下珠酸和金丝桃苷B和D中高度氧化的环己烷环中所发现的立体化学阵列。