Nitrile oxide cycloaddition to 4-hydroxy-2-cyclopentenone: Solvent effect and selectivity

The facial selectivity in the nitrile oxide cycloaddition reactions of 4-hydroxy-2-cyclopentenone and its bulky t-butyloxy derivative is reported. A quantitative evaluation of the solvent effect on the hydrogen bonding directing ability is given, showing the presence of some syn-stereoselectivity even in good H-bond acceptor solvents. The stereoselectivities of the o-t-butyl derivative may serve as reference data for more complex systems and point to the existence of a sole steric effect on the directivity; M(II) ions did not significantly improve the selectivity. The results are also discussed in light of the potential application of these scaffolds in the nucleoside analogue synthesis. (C) 2017 Elsevier Ltd. All rights reserved.