Lehrstuhl für Organische Chemie I, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany.
J Org Chem. 2011 Aug 5;76(15):5924-35. doi: 10.1021/jo201066d. Epub 2011 Jul 7.
The simple diastereoselectivity and the regioselectivity of the [2 + 2]-photocycloaddition of alk-3-enyl tetronates were studied, depending on the nature of the substituent R in the α-position. Fourteen tetronates were synthesized and their intramolecular photocycloaddition reactions performed. If R was an alkoxycarbonyl group and if the olefin, which underwent the intramolecular addition, was sterically congested, crossed photoproducts prevailed and were formed in yields between 35 and 65%. In all other cases, the straight photoproducts were obtained as the main reaction products in yields ranging from 39 to 84%. The structures of the photochemical products were thoroughly investigated by one- and two-dimensional NMR experiments. In all cases, the diastereoselectivitiy was excellent and only a single diastereoisomer was formed. A mechanistic model is proposed, which explains the regioselectivity of the [2 + 2]-photocycloaddition reaction.
研究了α位取代基 R 的性质对烷-3-烯基四唑的[2+2]光环加成的立体选择性和区域选择性的影响。合成了 14 个四唑，并进行了它们的分子内环加成反应。如果 R 是烷氧基羰基，并且经历分子内加成的烯烃是空间拥挤的，那么交叉光产物占优势，并以 35%至 65%的产率形成。在所有其他情况下，直光产物作为主要反应产物以 39%至 84%的产率获得。通过一维和二维 NMR 实验彻底研究了光化学产物的结构。在所有情况下，立体选择性都很好，只形成了单一的非对映异构体。提出了一种反应机理模型，该模型解释了[2+2]光环加成反应的区域选择性。
