Enantioselective Lewis Acid Catalysis of Intramolecular Enone [2+2] Photocycloaddition Reactions
Enantioselective Lewis Acid Catalysis of Intramolecular Enone [2+2] Photocycloaddition Reactions
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DOI：
10.1126/science.1244809
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发表时间：
2013-11-15
期刊：
影响因子：
56.9
通讯作者：
Bach, T.
中科院分区：
文献类型：
--
作者：
Brimioulle, R.;Bach, T.
光化学环加成反应的不对称催化受到抑制非选择性背景反应的挑战的限制。在这里，我们报告的高横截面的5，6-二氢-4-吡啶酮，一个多功能类的烯酮基板，π π * 过渡经历了一个>50纳米（nm）的红移吸收后，刘易斯酸配位。基于这一观察，在366 nm波长下照射时，使用0.5当量的手性刘易斯酸，用这些底物实现了对映选择性分子内[2+2]光环化加成反应（82 - 90%对映体过量）。其中一个产物作为关键中间体应用于（+）-羽扇豆碱的全合成和（+）-苦马豆碱的正式合成。几种烯酮在刘易斯酸存在下显示出类似的红移，表明手性刘易斯酸催化可能是对映选择性烯酮[2+2]光环加成的一般方法。
Asymmetric catalysis of photochemical cycloadditions has been limited by the challenge of suppressing the unselective background reaction. Here, we report that the high cross-section pi pi* transition of 5,6-dihydro-4-pyridones, a versatile class of enone substrates, undergoes a >50 nanometer (nm) bathochromic absorption shift upon Lewis acid coordination. Based on this observation, enantioselective intramolecular [2+2] photocycloaddition reactions (82 to 90% enantiomeric excess) were achieved with these substrates using 0.5 equivalents of a chiral Lewis acid upon irradiation at a wavelength of 366 nm. One of the products was applied as a key intermediate in the total synthesis of (+)-lupinine and the formal synthesis of (+)-thermopsine. Several enones show similar bathochromic shifts in the presence of a Lewis acid, indicating that chiral Lewis acid catalysis may be a general approach toward enantioselective enone [2+2] photocycloadditions.