Divergent synthesis of fully substituted isoxazoles and spiro-fused pyrazolin-5-ones from cyclopropyl oximes
摘要:
Efficient and divergent synthesis of fully substituted isoxazoles and spiro-fused pyrazolin-5-ones is developed from cyclopropyl oximes based on selection of reaction conditions. Under Appel conditions (PPh3/CBr4), substituted isoxazoles were synthesized from cyclopropyl oximes via a ring-opening and intramolecular cyclization process, whereas by treatment of cyclopropyl oximes with p-toluenesulfonyl chloride in the presence of potassium hydroxide, spiro-fused pyrazolin-5-ones were obtained via tandem ketoxime tosylation and intramolecular cyclization. (C) 2011 Elsevier Ltd. All rights reserved.
Abstract A facile and efficient synthesis of fully substituted 5-aminoisoxazoles was developed from α-cyclopropyl β-oximyl amides in the presence of triflic anhydride (Tf2O) in DMF under very mild conditions. The process involves sequential ring-opening and intramolecular cyclization reactions. A facile and efficient synthesis of fully substituted 5-aminoisoxazoles was developed from α-cyclopropyl
Facile and efficient synthesis of 5-iminooxazolines from α,α-disubstituted β-oximyl amides mediated by triflic anhydride (Tf2O) in the presence of 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) in dichloromethane at room temperature is developed, and a mechanism involving tandem Beckmann rearrangement and intramolecular cyclization reaction is proposed. Facile and efficient synthesis of 5-iminooxazolines
A convenient and efficient synthesis of spiro-fused pyrazolin-5-one N-oxides starting from readily available 1-carbamoyl-1-oximylcycloalkanes is developed. This general protocol features a novel and facile way for access to the five-membered azaheterocycles by formation of a new N-N single bond. The key cyclization step utilizes the formation of an N-oxonitrenium intermediate, mediated by the hypervalent iodine reagent PIFA, and its subsequent intramolecular trapping by the amide moiety under rather mild experimental conditions.