Iron Lewis Acid Catalyzed Reactions of Aromatic Aldehydes with Ethyl Diazoacetate:  Unprecedented Formation of 3-Hydroxy-2-arylacrylic Acid Ethyl Esters by a Unique 1,2-Aryl Shift

Abstract

The iron Lewis acid [η 5 -(C 5 H 5 )Fe(CO) 2 (THF)]BF 4 (1) was found to catalyze reactions of ethyl diazoacetate (EDA) and aromatic aldehydes, yielding 3-hydroxy-2-arylacrylic acid ethyl esters and the corresponding -keto esters. According to the literature, this is the first report of the formation of enol esters from EDA and aromatic aldehydes. The yield of the enol esters increased with electronrich aldehydes. With 2,4-dimethoxybenzaldehyde the only product isolated was the corresponding enol ester in 80% yield. However, in the presence of electron-deficient aldehydes such as p-nitrobenzaldehyde, formation of enol ester decreased to 32%. The most unique feature of these reactions is that enol esters are formed by an unusual 1,2-aryl shift, from a possible intermediate 8, which in turn is formed from the reaction of the iron aldehyde complex 7 and EDA.

Iron‐Catalyzed Aminomethyloxygenative Cyclization of Hydroxy‐α‐diazoesters with N,O‐Aminals

“…In accordance with precedent studies and our experimental results, a plausible mechanism for the formation of 3aa is proposed (Scheme ). In the first stage, the iminium I could be generated from N , O ‐aminal 2a under the assistance of Fe(OTf) 2 .…”

Recent chemistry of the η5-cyclopentadienyl dicarbonyl iron anion

“…Hossain and Mahmood synthesized [33] the methyl Fp complex for conversion to an iron Lewis acid (Fp + ·THF BF 4 − ) catalyst. The catalyst promoted reactions between aromatic aldehydes and ethyl diazoacetate to form acrylic acid ethyl esters and ␤-keto esters.…”

“…In another method reported by Mahmood and Hossain, 6.0 g (0.017 mol) of Fp 2 dimer is dissolved in 45 mL of THF and a 1% Na/Hg amalgam containing 1.28 g (0.055 mol) of Na metal is added and stirred at room temperature for 1.5 h. The reaction mixture is then cooled to −78 • C, whereby the amalgam solidifies and the NaFp/THF solution is transferred to another flask. Upon warming to 0 • C, 8.0 g (0.056 mol) methyl iodide is added dropwise and allowed to stir for 1 h. Removal of the THF solvent, chromatographic separation by pentane, and removal of the pentane solvent provided 5.85 g of the Fp methyl complex in 90% yield (Scheme 4) [33].…”

Synthesis and characterization of amine complexes of the cyclopentadienyliron dicarbonyl complex cation, [Cp(CO)2Fe]+

“…A particular example is the ethereal complex, [CpFe-(CO) 2 (THF)]BF 4 [34] in which the labile tetrahydrofuran (THF) is coordinated to the metal centre through the oxygen atom. This complex has been proven to be an essential precursor in the synthesis of various cyclopentadienyliron complexes [4,[10][11][12][13][15][16][17][18][19][20]35], as well as catalysts in various organic syntheses such as the [2+2] cycloaddition of alkenes [36], Diels-Alder reactions [37,38], cyclopropanation [27,[31][32][33], epoxidation [29,30] and aziridination [25][26][27][28], among others [3,[22][23][24]27,29,39]. In all these reactions THF is easily displaced by the desired substrate to form either the desired intermediate or desired end product.…”

“…The cationic complexes of type, [CpFe(CO) 2 L] + (L = labile ligand) [1][2][3][4] are an important class of transition metal compounds that have been extensively utilized in synthesis [2,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and catalysis [3,14,[22][23][24][25][26][27][28][29][30][31][32][33]. A particular example is the ethereal complex, [CpFe-(CO) 2 (THF)]BF 4 [34] in which the labile tetrahydrofuran (THF) is coordinated to the metal centre through the oxygen atom.…”