An Intramolecular Cycloetherification of Unactivated Olefinic Substrates Bearing endo-Alcohol: Access to Diversely...

Herein, we report an efficient and rapid synthetic methodology to access diversely substituted oxa-cages from unactivated olefinic substrates derived from endo-norbornenes by employing Lewis acid- (BF₃  ⋅ OEt₂ ) or base (NaH)-promoted intramolecular etherification. Although both BF₃  ⋅ OEt₂ and NaH are found to be efficient for this transformation, slightly better yields and less reaction times are achieved with NaH/DMF (0.25-1 h at 100 °C) as compared to BF₃  ⋅ OEt₂ /DCM (2-3 h at 0 °C to rt). The evolution of this intramolecular cyclization was studied by time-dependent NMR studies in CDCl₃ solvent. Further, these observations are supported by infrared (IR) spectral data. It is worth mentioning that the present methodology enables a new route to assemble highly fused oxa-cage systems by choosing suitably substituted oxa-cage compounds for the olefin-metathesis sequence. The highly fused oxa-cage systems may have potential applications in high-energy-density materials (HEDMs) and supramolecular chemistry.