CpRu^IIPF₆/Quinaldic Acid-Catalyzed Chemoselective Allyl Ether Cleavage. A Simple and Practical Method for Hydroxyl Deprotection

Abstract

A cationic CpRu(II) complex in combination with quinaldic acid shows high reactivity and chemoselectivity for the catalytic deprotection of hydroxyl groups protected as allyl ethers. The catalyst operates in alcoholic solvents without the need for any additional nucleophiles, satisfying the practical requirements of operational simplicity, safety, and environmental friendliness. The wide applicability of this deprotection strategy to a variety of multifunctional molecules, including peptides and nucleosides, may provide new opportunities in protective group chemistry. [structure: see text]

[CpRu(IV)(π‐C3H5)(2‐quinolinecarboxylato)]PF6 Complex: A Robust Catalyst for the Cleavage and Formation of Allyl Ethers

“…[3] These indispensable prerequisites often decrease the practicality of the complexes in terms of chemoselectivity, reactivity, operational simplicity, and product isolation, among others. The disadvantages have been recently overcome to a great extent by the development of a new catalyst system consisting of [CpRu(CH 3 CN) 3 ]PF 6 (3) and 2-quinolinecarboxylic acid (4). [4,5] This catalyst functions as a highly reactive cleaver of allyl ether in alcoholic solvents under very mild and additive-free conditions.…”

“…The disadvantages have been recently overcome to a great extent by the development of a new catalyst system consisting of [CpRu(CH 3 CN) 3 ]PF 6 (3) and 2-quinolinecarboxylic acid (4). [4,5] This catalyst functions as a highly reactive cleaver of allyl ether in alcoholic solvents under very mild and additive-free conditions. Furthermore, by using non-alcoholic solvents or no solvent, the highly efficient catalytic dehydrative allylation of alcohols with 2-propen-1-ol can be achieved.…”

“…[4,6] The CpRu(II)-4-catalyzed reactions are thought to proceed via an intermediate catalyst -substrate complex, which is generated via olefin-mediated coordination of 2-propan-1-ol onto a CpRu(II)/2-quinolinecarboxylic acid species 5. Here, a hydrogen bond is formed between the COOH moiety of the catalyst part and the OH group of 2-propen-1-ol, and the s-donative sp 2 -N atom of the quinoline moiety and the monoanionic h 5 -Cp ligand strongly coordinate to the Ru ion.…”

“…Here, a hydrogen bond is formed between the COOH moiety of the catalyst part and the OH group of 2-propen-1-ol, and the s-donative sp 2 -N atom of the quinoline moiety and the monoanionic h 5 -Cp ligand strongly coordinate to the Ru ion. [4,6] These simultaneous events synergistically enhance the electrophilicity of C(3) and the nucleophilicity of Ru, [9] thereby accelerating the generation of the cationic CpRu(IV)(p-C 3 H 5 ) carboxylate species 6.…”

“…The complex can be quantitatively prepared via an easy and simple one-pot synthesis and can be kept for a long time without protection from air and moisture with no loss of catalytic activity. In comparison to the original Ru(II)-based method, [4,6] the advantages afforded by the new complex 6 should further enhance the practical value of allyl ethers for hydroxy protection in organic synthesis.…”