Acid-mediated transformation of spirocyclopropyl oxetanes: a facile approach to spirocyclopropyl butenolides and γ-butyrolactones

Abstract

Spirocyclic oxetanes were found to undergo versatile transformations under different acid-mediated conditions. Treatment of spirocyclopropyl oxetanes with excess amounts of hydrochloric or hydrobromic acid at room temperature resulted in the formation of spirocyclopropyl fused butenolides with good yields. The transformation of spirocyclopropyl oxetanes mediated by hydroiodic acid led to spirocyclopropyl fused c-butyrolactones instead of butenolides. Transformation of spirocyclopropyl oxetanes catalyzed by Lewis acid was also explored and found to give distinct products such as spirobutyl indolinones. The reaction mechanisms involved in the acid-mediated transformations were proposed.3 Electronic supplementary information (ESI) available: X-ray structure of compound 17; 1 H NMR and 13 C NMR spectra of all new compounds. CCDC 905935-905938. For ESI and crystallographic data in CIF or other electronic format see a 100 equiv. of acid were used. b isolated yields.Scheme 2 Proposed mechanism for HCl mediated transformation of 1a into 2. 7530 | RSC Adv.,

Iodine and Iodide in Reductive Transformations

“…Zhang et al. developed a reductive approach for accessing γ‐butyrolactones, which featured HI as a rearrangement promoter and reductant (Scheme 31a) [79] . HCl or HBr are not suitable, as butenolides are obtained instead.…”

“…Zhang et al developed a reductive approach for accessing γ-butyrolactones, which featured HI as a rearrangement promoter and reductant (Scheme 31a). [79] HCl or HBr are not suitable, as butenolides are obtained instead. Brønsted acid activation of the benzylic CÀ O bond and iodide installation, followed by nucleophilic acyl substitution and reductive deiodination on the benzylic center, delivers the γ-butyrolactone framework (Scheme 31b).…”

Ring Expansions of Oxiranes and Oxetanes

“…The final oxetane ring expansion example utilizes quite unusual oxetane precursors (Scheme 47) [58]. Professor Zhang uses oxetanes with no less than a spiro group at every single position, including a key cyclopropylspiro group at the 3-position.…”

Recent Applications of Oxetanes in the Synthesis of Heterocyclic Compounds

“…In another example of the utility of oxaspirohexane systems, Zhang reported acid-mediated ring expansions of spirocyclopropyl oxetanes (Scheme 5b). 15 When a series of these oxaspirohexanes was treated with HCl or HBr, spirocyclopropyl-fused butenolides were formed. When HI/I 2 was used, spirocyclopropyl fused γ-butyrolactones were obtained in high yields.…”