Cerium Ammonium Nitrate (CAN) for Mild and Efficient Reagent to Remove Hydroxyethyl Units from 2‐Hydroxyethyl Ethers and 2‐Hydroxyethyl Amines.

Abstract

Deprotection O 0345 Cerium Ammonium Nitrate (CAN) for Mild and Efficient Reagent to Remove Hydroxyethyl Units from 2-Hydroxyethyl Ethers and 2-HydroxyethylAmines. -The recently published protocol concerning the cleavage of 2-hydroxyethyl ethers by treatment with CAN is reviewed in detail and extended to 2-hydroxyethyl amines, cyclic relatives and proline derivatives. -(FUJIOKA*, H.; HIROSE, H.; OHBA, Y.; MURAI, K.; NAKAHARA, K.; KITA, Y.; Tetrahedron 63 (2007) 3, 625-637; Grad. Sch. Pharm. Sci., Osaka Univ., Suita, Osaka 565, Japan; Eng.) -Nuesgen 18-047

Diastereoselective Desymmetrization of Symmetric Dienes and its Synthetic Application

“…This reaction stereoselectively proceeded via the chiral bicyclic cationic intermediates, and the subsequent nucleophilic addition of an alcohol to the oxonium ion intermediate afforded 59, which have two newly formed chiral centers on the prochiral atom and the acetal center of the starting materials 58. The chiral auxiliary unit derived from the C 2 -symmetric diol could be removed by various procedures, i.e., Birch reduction, hydrogenolysis, and fragmentation promoted by CAN [38,39] We then studied the intramolecular bromoetherification reaction of the substituted cyclohexadiene having the C 2 -symmetric acetal 60 and found that the reaction successfully discriminated the two prochiral olefins in a stereoselective manner to provide 61 in 63% yield [40,41] (Scheme 22). This reaction was useful for constructing complex molecules because it could produce optically active cyclohexane derivatives bearing multiple chiral centers and the remaining olefin, which promised further transformations.…”

“…The 8-membered acetal 78 was converted to the lactone 79. Removal of the chiral auxiliary with CAN, developed in our laboratory [38,39], followed by epoxidation of the resulting alcohol with Ag 2 O afforded 80. The treatment of the epoxide 80 with the corresponding Grignard reagent, and further transformation to furnish the synthesis of rubrenolide and rubrynolide (Scheme 29).…”