An Intramolecular Cycloetherification of Unactivated Olefinic Substrates Bearing endo‐Alcohol: Access to Diversely Alkylated Oxa‐Cage Derivatives Useful for Olefin‐Metathesis

Abstract

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-(BF 3 • OEt 2 ) or base (NaH)promoted intramolecular etherification. Although both BF 3 • OEt 2 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 BF 3 • OEt 2 /DCM (2-3 h at 0 °C to rt). The evolution of this intramolecular cyclization was studied by time-dependent NMR studies in CDCl 3 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.

Synthetic Studies to Fused 5/5/6‐Tricyclic Frameworks: Access to Presilphiperfolanol Analogues and A, B, C‐Ring System of Lycopodium Alkaloids and Cyclopiane Diterpenes

“…Instead, a mixture of cyclic ether 30 & RCM product 31 (yield of mixture 91 %), 34 & 35 (yield of mixture 88 %), and 38 & 39 (yield of mixture 93 %) were obtained in good yields. [26] Here, we could not separate compounds 30 & 31 by traditional column chromatography. However, compound 35 was isolated in small quantities with reasonable purity to generate the NMR data.…”

“…Here, the keto compounds 11 and 12 are derived from tricyclic ketone 10 by an alkylation sequence (Scheme 1). [26] Figure 4. Some Commonly Used Ru-Based Catalysts for Olefin-Metathesis.…”

“…Here, products 30 and 31 were detected and confirmed based on NMR spectral data. [26] Compound 30 shows one multiplet at δ 4. 25-4.22 (m, 1H) corresponds to HÀ C6À OÀ C1, and compound 31 exhibits two doublet of doublets at δ 6.48 (dd, J = 5.40, 3.31 Hz, 1H), 6.12 (dd, J = 5.48, 3.30 Hz, 1H) which corresponds to norbornene double bond (C5À C6) with diagnostic peaks.…”

“…Along similar lines, compounds 34 and 35 were identified and confirmed by NMR spectral data. [26] The 1 H NMR spectral data comparison of compounds 25, 30, and 31 is shown in Figure 7. [26] Similarly, the 1 H NMR comparison of compounds 26, 34, and 35 are shown in Figure 8 > .…”

“…[26] The 1 H NMR spectral data comparison of compounds 25, 30, and 31 is shown in Figure 7. [26] Similarly, the 1 H NMR comparison of compounds 26, 34, and 35 are shown in Figure 8 > . [26] Since, the direct RCM between the two allyl groups and intramolecular etherification over ROM preventing RRM/tandem-metathesis, we have changed our strategy to realize RRM/ tandem-metathesis products 28 and/or 29, 32 and/or 33, and Scheme 5.…”