Sliwinska Anna, Czardybon Wojciech, Warkentin John
Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada.
Org Lett. 2007 Feb 15;9(4):695-8. doi: 10.1021/ol063021s. Epub 2007 Jan 23.
2,2-Dimethoxy-3,3-dicyanospiro[cyclopropane-1,9'-[9H]fluorene] reacted fast with methanol to afford 9-trimethoxymethyl-9-dicyanomethyl-9H-fluorene. Reaction with benzaldehydes also gave products of cyclopropane ring opening. Strong electron-donor p-substituents or a strong attractor enhanced the rate. Ring opening of the cyclopropane to a zwitterion that recloses or reacts with an aryl aldehyde, to form either a CO or a CC bond first, can explain the result. The former mode of closure is sensitive to p-substituents because they are directly conjugated to the positive charge at the benzylic carbon of the former aldehyde. The latter mode is sensitive to the ground-state electrophilicity of the carbonyl carbon of the former aldehyde. Thus, reaction of the cyclopropane with p-substituted aldehydes is accelerated by either electron-donor or -acceptor substituents. [reaction: see text].
2,2-二甲氧基-3,3-二氰基螺[环丙烷-1,9'-[9H]芴]与甲醇快速反应，生成9-三甲氧基甲基-9-二氰基甲基-9H-芴。与苯甲醛反应也得到环丙烷开环产物。强供电子对取代基或强吸电子基会提高反应速率。环丙烷开环形成两性离子，该两性离子重新闭环或与芳基醛反应，首先形成C=O或C-C键，这可以解释该结果。前一种闭环模式对对位取代基敏感，因为它们直接与前一个醛的苄基碳上的正电荷共轭。后一种模式对前一个醛的羰基碳的基态亲电性敏感。因此，环丙烷与对位取代醛的反应会因供电子或吸电子取代基而加速。[反应：见正文]
