The β-Fluorine Effect. Electronic Versus Steric Effects in Radical Deoxygenations of Fluorine-Containing Pentofuranose Nucleosides
作者:Stanislaw F. Wnuk、Dania R. Companioni、Vladimir Neschadimenko、Morris J. Robins
DOI:10.1021/jo020428b
日期:2002.12.1
Stereoselective pyramidalization of free radicals by a vicinal fluorine substituent, the beta-fluorine effect, was invoked to rationalize a 77:23 anti/syn ratio of 2-deuterio-1-fluorocyclopentanes obtained by radical reduction of trans-2-fluoro-1-bromocyclopentane with tributyltin deuteride (Dolbier, W. R., Jr.; Bartberger, M. D. J. Org. Chem. 1995, 60, 4984-4985). We have evaluated analogous reductions
借助邻位氟取代基对自由基进行立体选择性锥体化,即β-氟效应,以合理化通过反式-2-氟-1-基的自由基还原而获得的2-氘-1-氟环戊烷的77:23反/同比例。溴环戊烷和氘化三丁基锡(Dolbier,WR,Jr .; Bartberger,MDJ Org.Chem。1995,60,4984-4985)。我们已经评估了某些腺嘌呤2'(3')-氟-3'(2')-O-苯氧基硫羰基核苷衍生物的四种可能的立体异构体的类似还原。在所有情况下,腺嘌呤在β面上的立体作用都将氘从锡烷转移到呋喃糖环的α面上的C2'(C3')。然而,β-氟效应增加了氘转移与邻位氟取代基的比率。