An efficient method for <i>retro</i>-Claisen-type C–C bond cleavage of diketones with tropylium catalyst
作者:M. A. Hussein、V. T. Huynh、R. Hommelsheim、R. M. Koenigs、T. V. Nguyen
DOI:10.1039/c8cc07329e
日期:——
cleavage in this reaction is usually promoted by a number of transition-metal Lewis acid catalysts or organic Brønsted acids/bases. Herein we report a new convenient and efficient method utilizing the tropylium ion as a mild and environmentally friendly organocatalyst to mediate retro-Claisen-type reactions. Using this method, a range of synthetically valuable substances can be accessed via solvolysis of
iron(III) triflate, Fe(OTf)3, copper(II) triflate, Cu(OTf)2, and silver(I) triflate, AgOTf, show high catalytic activities. These reactions proceed through the carbon–carbonbondcleavage by a retro‐aldol reaction and were found to be highly regioselective even in the presence of other functional groups. This type of reaction can also be applied to the preparation of the keto esters during the synthesis
excellent yields. The reaction tolerates a wide range of functional groups, such as olefins, alkynes, halides, nitro and esters. Furthermore, the protocol allows late-stage acetylation of naturally occurring alcohols. The methodology provides a practical approach for large scale synthesis of esters using fixed-bed continuous process. The catalyst can be recovered from the reaction mixture and reused up
An iron(III) salt catalyzed retro-Claisencondensation between an alcohol and a 1,3-diketone was investigated. The mechanism involves the formation of a metal-induced six-membered cyclic transition state and cleavage of the C–C bond. Regioselective esterification and one-pot conversion of silyl ethers into esters with good yields was observed. Simple reaction conditions, high yields, and broad scope