Fluorination often confers a range of advantages in modulating the conformation and reactivity of small molecule organocatalysts. By strategically introducing fluorine substituents, as part of a β-fluoroamine motif, in a triazolium pre-catalyst, it was possible to modulate the behaviour of the corresponding N-heterocyclic carbene (NHC) with minimal steric alterations to the catalyst core. In this study, the effect of hydrogen to fluorine substitution was evaluated as part of a molecular editing study. X-ray crystallographic analyses of a number of derivatives are presented and the conformations are discussed. Upon deprotonation, the fluorinated triazolium salts generate catalytically active N-heterocyclic carbenes, which can then participate in the enantioselective Steglich rearrangement of oxazolyl carbonates to C-carboxyazlactones (e.r. up to 87.0:13.0).
氟化通常在调节小分子有机催化剂的构象和反应性方面带来一系列优势。通过在三唑前驱催化剂中战略性地引入氟取代基,作为β-氟胺基团的一部分,可以调节相应的N-杂环卡宾(NHC)的行为,同时最小程度地改变催化剂核心的立体构型。在这项研究中,氢到氟的取代效应被作为分子编辑研究的一部分进行评估。对多个衍生物进行了X射线晶体学分析,并讨论了构象。去质子化后,氟化三唑盐会产生具有催化活性的N-杂环卡宾,这些卡宾随后可以参与对氧唑基碳酸酯的对映选择性Steglich重排反应,生成C-羧基氮内酯(对映选择性达到87.0:13.0)。