| Abstract
| - Stereoselective pyramidalization of free radicals by a vicinal fluorine substituent, the β-fluorineeffect, was invoked to rationalize a 77:23 anti/syn ratio of 2-deuterio-1-fluorocyclopentanes obtainedby 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 analogousreductions of the four possible stereoisomers of some adenine 2‘(3‘)-fluoro-3‘(2‘)-O-phenoxythiocarbonyl nucleoside derivatives. In all cases, the steric effect of adenine on the β face directs deuteriumtransfer from the stannane to C2‘(C3‘) on the α face of the furanose ring. However, the β-fluorineeffect enhances ratios of deuterium transfer anti to the vicinal fluorine substituent.
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