Tropylium-Catalyzed O–H Insertion Reactions of Diazoalkanes with Carboxylic Acids

Abstract

Herein, we describe the application of a nonbenzenoid aromatic carbocation, namely tropylium, as an organic Lewis acid catalyst in O−H functionalization reactions of diazoalkanes with benzoic acids. The newly developed protocol is applicable to a wide range of diazoalkane and carboxylic acid substrates with excellent efficiency (43 examples, up to 99% yield).

Tropylium-Promoted Hydroboration Reactions: Mechanistic Insights Via Experimental and Computational Studies

“…Given our ongoing interest in the chemistry of tropylium ion and our recent recognition of the similarity in Lewis acid catalyst activity of tropylium ion to boron Lewis acids B­(Ar F ) 3 , which are known as efficient catalysts for hydroboration reactions, ,− ,, we envisioned that tropylium salts could potentially serve as suitable organocatalysts for the same chemical transformation. In addition to its Lewis acidity, tropylium ion is also known as an organic oxidant, which could abstract a hydride from borane reagents to trigger the reaction via the formation of borenium cation (Scheme c).…”

Asymmetric synthesis of isochromanone derivatives via trapping carboxylic oxonium ylides and aldol cascade

“… 4 To this end, enantioselective trapping of oxonium ylides initiated by the insertion of phenols and alcohols, one of the most common and important species, has been well studied. 5 However, carboxylic oxonium ylides are largely undeveloped ( Scheme 1a ), 6,8 and sporadic racemic cascade reactions by bypassing the competitive O–H insertion step (path I) 7 have been disclosed, such as intermolecular trapping with imines (path II) 6 a and intramolecular aldol cascade to produce lactones (path III and IV). 6 c The enantioselective trapping of carboxylic oxonium ylides is rare with difficulties such as (1) low p K a values of protonated carboxylic acids in the zwitterionic intermediate leads to a rapid proton shift; 8 (2) changing the electronics of the diazo-derived rhodium carbenoid to delay the proton shift and to facilitate additional cascade results in a strong racemic background reaction.…”

Main Group Catalysis: Cationic Si(II) and Ge(II) Compounds as Catalysts in Organosilicon Chemistry

“…In order to move towards sustainable and environmentally friendly catalyst systems, attractive candidates would be the lighter p-block compounds. In the last decade, Lewis-acidic compounds based on boron (recent articles and reviews [7][8][9][10]), carbocations (recent articles and reviews [11][12][13][14]), phosphorus(III) and (V) cations (recent articles and reviews [15][16][17][18]), including frustrated Lewis pairs (FLPs) (recent articles and reviews [19][20][21]), have moved into the focus of catalysis.…”